International Journal of Sport and Exercise Science, 1(2): 19-26 19

Effects of Magnesium Sulfate on Dynamic Changes in Blood Glucose Levels and Glucose Transporter-3 Expression in the Striatum during Short-term Forced Swimming in Gerbils

1 2,* I-Ju Chen , Shiu-Min Cheng

1Department of Physical Education, Asia University, Taichung, Taiwan, 413, ROC 2Department of Psychology, Asia University, Taichung , Taiwan, 413, ROC Received 20 Jan 2010; Accepted 28 Feb 2010

Abstract In a previous study, we reported that when gerbils were subjected to a period of forced swimming, glucose levels and magnesium levels in the plasma became elevated. In addition, a pretreatment with magnesium sulfate increased the expression of glucose transporter-3 (GLUT-3) in the cortex. The goal of the present study was to evaluate dynamic changes in blood glucose, lactate and magnesium levels in gerbils that had been subjected to short-term forced swimming using an auto-blood-sampling system. A second goal was to investigation the effects of forced swimming and magnesium sulfate on GLUT-3 expression, glucose and magnesium levels in the striatum, which is involved in energy delivery and motor function. Data collection involved the use of a microdialysis analyzer, a flame atomic absorption spectrometer and western blotting assays to detect glucose, lactate, magnesium and GLUT-3 levels, respectively. Gerbils were subjected to a blood sampling assay and pretreated with saline (n=6) or magnesium sulfate (n=6, 90 mg·kg -1, ip) 30 min before the period of forced swimming. Whole blood glucose, lactate, and magnesium levels increased to 175% and 235%, 305% and 190%, and 102% and 128% of basal levels during swimming in both the control and magnesium sulfate-treated groups (p<0.05). The glucose and magnesium levels during swimming were 60% and 26% greater in the magnesium sulfate-treated group (p<0.05), respectively, whereas the lactate levels were attenuated at 115% (p<0.05). Another group of gerbils was subjected to a brain sampling assay. The gerbils were separated into four groups (n=4, each group): control group (C group) pretreated only with saline; magnesium sulfate group (Mg group) pretreated only with magnesium sulfate; saline control and forced swimming group (C+S group) pretreated with saline 15 min prior to the forced swimming period then rested for 30 min; the magnesium sulfate plus the forced swimming group (Mg+S group) was pretreated with magnesium sulfate 15 min prior to the forced swimming period then rested for 30 min. The results indicated that GLUT-3 and magnesium levels were slightly, but not significantly higher in the Mg group, the C+S group and the Mg+S group. These data suggest that magnesium increased whole blood glucose and magnesium levels during forced swimming; however, the effects of magnesium and swimming on GLUT-3 protein expression varied in different regions of the brain.

Keywords : Forced swimming, Glucose transporter, Magnesium, Striatum

Accumulating evidence indicates the existence of a direct Introduction relationship between the redistribution of magnesium in the Magnesium (Mg), the second most abundant intracellular body and the type of exercise and that the status of magnesium cation, functions as a cofactor in more than 300 enzymatic influences the nature of this redistribution [5,6]. reactions. Magnesium is also involved in cellular energy In general, long-term exercise or exercise until exhaustion production, neuromuscular functions, glycogen breakdown, and results in hypomagnesaemia and hypoglycaemia [7,8], whereas modulating the activity of adenosine triphosphatase, providing short-term and high-intensity exercise induces energy for cells [1-3]. Thus, the relationship between hypermagnesaemia and hyperglycaemia [9-11]. Conflicting magnesium status and exercise has received significant findings regarding on the effect of exercise on erythrocyte research attention. Magnesium depletion may lead to changes concentration have been reported. A mechanism for the in neuromuscular function and reductions in physical observed decrease in plasma magnesium concentration after performance and the efficiency of energy metabolism [4]. long term physical exercise could be a shift of Mg into erythrocytes. However, in several studies a decrease in plasma * Corresponding author: Shiu-Min Cheng Mg was not accompanied by an increase in erythrocyte Mg Tel: +886-4-23323456 ext. 3252 [9,12]. In our previous study, we reported that short-term Fax: +886-4-23321057 forced swimming results in an increase in plasma glucose and E-mail: [email protected] magnesium levels in gerbils [13]. Short-term, high intensity 20 International Journal of Sport and Exercise Science, Vol. 2. No.1 2010

exercise transiently increased plasma magnesium Forced swimming concentrations as the consequence of a decrease in plasma The gerbils were randomly divided into a control (saline) volume [6,9]. The two major fractions of whole blood are group or a magnesium sulfate supplement group. Saline or plasma and erythrocytes. Therefore, the aim of this study was magnesium sulfate (90 mg ·kg -1, intraperitoneal injection) was to measure the dynamic levels of whole blood magnesium, injected 30 min prior to the forced swimming task. Each gerbil glucose and lactate levels in gerbil subjected to forced was placed on a polystyrene board floating in a Plexiglas swimming using an auto-blood-sampling system coupled to a cylinder that was 40 cm in diameter, 35 cm in height, and filled microdialysis analyzer. with warm water (about 35 °C, no heat loss or gain occurred) to Glucose is an essential energy source for most cells and is a height of 18 cm [13]. The polystyrene board was then the primary energy source for brain tissue during exercise. As removed gently, and each gerbil was forced to swim for 15 min Glucose is a hydrophilic molecule, the facilitated diffusion of (if a gerbil was judged to be immobile, i.e., when it floated glucose across the plasma membrane is mediated by a family of passively with the head above water, it was allowed to rest for specific glucose transporters (GLUTs). To date, 13 members of 10 sec, and then forced to continue with the swimming this family of transporters have been identified [14-17]. exercise). After the forced swimming period, each gerbil was GLUT-3 and GLUT-5 are major glucose tansporter isoforms in removed from the water, and then carefully and rapidly dried the brain. GLUT-3 (a 496-amino-acid isoform) is a with a towel and a hair blower. In the first experiment, each high-affinity isoform largely expressed in neurons where it is gerbil was then placed on the polystyrene board again, and believed to be the predominant glucose transporter isoform; blood samples were collected during the 3 h recovery period. In GLUT-5 is expressed in microglia. On the other hand, the second experiment, each gerbil was placed on the magnesium regulates glycolysis [1], and we have reported that polystyrene board again, and allowed to rest for 30 min before magnesium supplementation enhanced glucose and GLUT-3 sacrificing. The gerbils were quickly decapitated and their levels in the cortex of gerbil [18]. Moreover, using a brains were removed and frozen (a diagram is shown in Fig. 1). microdialysis technique, we found that magnesium sulfate increased extracellular glucose levels in the striatum of gerbils that had been subjected a short-term period of forced swimming [19]. As the striatum is involved in the control of motor function and energy delivery [20], magnesium sulfate supplementation was also employed to evaluate changes in the striatum levels of GLUT-3, glucose, and magnesium during short-term forced swimming in this study.

Materials and Methods Animals Adult and naïve male gerbils (n=28), weighing between 70 and 80 g, were obtained from the Laboratory Animal Center of the Taichung Veterans General Hospital. All animals were Figure 1. Brain sampling time procedures housed at a temperature of 25 °C in a light (12:12 h light-dark cycle)-controlled room with free access to rat chow and tap Auto-blood- sampling water. Animal care and experimental procedures (# La-95225, In the first experiment, blood samples were automatically TCVGH, Taiwan) were in accordance with the Guide for the collected via a catheter implanted in the jugular vein by a Care and Use of Laboratory Animals by the U. S. Department computer aided auto-blood sampling system (DR-II, Eicom, of Health and Human Services and with the policy statement Kyoto, Japan) in conscious, freely moving gerbils. Thirty µl regarding the care and use of experimental animals by the samples of whole blood were collected at 15 min intervals. In American College of Sports Medicine. The gerbils were order to preserve glucose, 15 µl of a NaF solution and 90 µl of randomly separated into two groups and subjected to two 1N HClO 4 were added to the whole blood sample, which was experiments. In the first experiment, gerbils (n=12) were then centrifuged at 1,000 g for 10 min at 4°C. 10 µl of Tris subjected to blood sampling during the forced swimming, and buffer was added to the aliquots of the supernatant (40 µl) and in the second experiment, the gerbils (n=16) were subjected to directly injected into the microdialysis analyzer (CMA/600, brain sampling. For each gerbil in the blood-sampling group, a Carnegie Medicin), equipped with a flame atomic absorption blunt dissection to clear the fat and connective tissue beside the spectrometer for detecting the concentrations of glucose, lactate jugular vein was performed. A length of PUC-40 tube was then and magnesium, respectively. connected to the jugular vein of each gerbil and blood was withdrawn according to the method described by Harms and Brain homogenization Ojeda [21]. The PUC-40 was connected to the DR-II, the In the second experiment, the gerbils (n=16) were randomly auto-blood-sampling device through a subcutaneous vein in the separated into four groups: saline control (C group, n=4), neck from the back. magnesium sulfate (Mg group, n=4), saline control plus short-term forced swimming (C+S group, n=4), and International Journal of Sport and Exercise Science, 1(2): 19-26 21

magnesium sulfate plus short-term forced swimming (Mg+S spectrometer (FAAS, Perkin-Elmer, Uberlingen, Germany) was group, n=4) groups. The saline control or magnesium sulfate used to quantitatively determine the content of magnesium. A groups (90 mg ·kg -1, intraperitoneal injection) were injected 30 25 µl aliquot of supernatant was diluted with 975 µl of 0.2% min before forced swimming. The C+S group was injected with HNO 3 for further analysis by FAAS. All reagents used were of saline, rested for 30 min, forced to swim for 15 min, and then analytical grade and were purchased from E. Merck. All allowed to rest for 30 min prior to sacrifice. The Mg+S group containers were soaked in 20% nitric acid, rinsed with water was injected with magnesium sulfate, rested for 30 min, forced and then dried in a clean room for later use. to swim for 15 min, and then rested for 30 min prior to sacrifice. Analysis of glucose and lactate levels After the forced swimming period, the gerbils were allowed A microdialysis analyzer (CMA/600, Carnegie Medicin, to rest for 30 min and were then sacrificed and the brains Stockholm, Sweden) was employed to determine glucose and removed. The striatum tissues were rapidly frozen on dry ice, lactate levels. Glucose and lactate were oxidized by glucose weighed, homogenized in ice-cold 1 N HCl, and the and lactate oxidase, respectively (Reaction 1 and 2, homogenate centrifuged twice (4°C, 10,000 rpm for 10 respectively). Peroxidase catalyses the reaction between the minutes). A 2 µl portion of Tris-buffer was added to 8 µl of the hydrogen peroxidase formed, phenol, and 4-amino-antipyrine supernatant to adjust the pH to about 7.0 for further glucose to form the red-violet colored quinoneimine, which can be analysis by the microdialysis analyzer. A 25 µl aliquot of the detected at 546 nm. supernatant was diluted with 975 µl of 0.2% HNO 3 for analysis for magnesium by Flame atomic absorption spectrometry. Statistical analysis All data are expressed as means±SEM. The first experiment Western bolt analysis used a repeated-measures two-way ANOVA and Fisher’s least Brain tissue (striatum) was placed in 2 ml of ice-cold lysis significant difference (FLSD) test were used to analyze buffer (0.32 M Sucrose, 1 mM EDTA, 50 mM Tris-Cl pH7.4, statistically significant differences between the saline control and a protease inhibitor cocktail from Boehringer Mannheim and the magnesium sulfate-treated groups. The second (Mannheim, Germany), and homogenized with a motor-driven experiment used one-way analysis of variance (ANOVA) glass homogenizer equipped with a Teflon pestle. The resulting followed by the Student-Newman-Keuls’ multiple-range test to brain homogenate was then centrifuged at 1,400g for 10 min. test the significance of difference among groups. Differences The resulting supernatant was centrifuged at 45,700g for 30 were considered to be statistically significant at p<0.05. min. The pellet, containing the plasma membrane fraction, was collected and washed twice with lysis buffer by repeating the Results above centrifugation. The final pellet was suspended in 1 ml of o lysis buffer and stored at -70 C. o The entire procedure was carried out at 4 C. Each lysate was applied to SDS-polyacrylamide gels and electrophoreses conducted at less than 10 % reducing gel conditions. The separated proteins were electroblotted onto Hybond-P: PVDF membranes (Amersham Biosciences, Piscataway, NJ, USA) using a Mini Trans-Blot Cell (Bio-Rad Laboratories, Hercules, CA) according to the manufacture's instructions. The membranes were then washed once with Tris-buffered saline (TBS, Bio-Rad Laboratories, Inc, USA), pH 7.2, containing 0.1% Tween-20 (TBS-T, Bio-Rad Laboratories, Inc, USA) and o blocked at room temperature (about 26 C) for 1 h with TBS-T containing 5% skimmed milk. Antibodies against GLUT-3 Figure. 2. The changes in blood levels of glucose. Data are presented as (Chemicon International, Inc, USA) were then added to give a the mean ±SEM (n=6). *p<0.05 and **p<0.01 compared with final dilution of 1/1500, respectively, in TBS-T containing 5% basal levels; #p<0.05 compared with the control group. skimmed milk. The membranes were incubated at room temperature for 2 h, washed three times with TBS-T, and The basal levels of whole blood glucose in the control and treated with horseradish peroxidase-conjugated goat anti-rabbit magnesium sulfate-treated groups during forced swimming are IgG (Santa Cruz Biotechnology, Santa Cruz, CA) in TBS-T shown in Figure 2. The glucose levels of the control group containing 5% skimmed milk for 1 h. Finally, after four washes increased to about 175% of the basal level (p<0.01) during the with TBS-T, the protein bands were visualized using an period of forced swimming, then returned to the basal level enhanced chemiluminescence Western blot analysis system after a 30 min recovery period. In the magnesium (Pierce, Rockfold, IL, USA). sulfate-treated group, the glucose levels immediately increased to 160%-180% of the basal levels (p<0.05) after magnesium Determination of magnesium concentrations sulfate treatment, gradually increased to 235% of the basal A Perkin-Elmer Model 5100 Flame atomic absorption levels (p<0.01) at post-exercise, and returned to the basal level at 60 min of recovery. The glucose levels for the magnesium 22 International Journal of Sport and Exercise Science, Vol. 2. No.1 2010

sulfate-treated group after swimming was about 60% greater The basal levels of whole blood magnesium in the control than those for the control group (p<0.05). and magnesium sulfate-treated groups were shown in Figure 4. In the magnesium sulfate-treated group, the magnesium levels increased to 128% after the swimming period (p<0.05) and then diminished to the basal levels within 30 min of recovery. The magnesium levels in the magnesium sulfate-treated group was 26% greater than those in the control group before swimming begun (p<0.05).

Figure 3. The changes in blood levels of lactate. Data are presented as the mean ±SEM (n=6). *p<0.05 and **p<0.01 compared with basal levels; #p<0.05 compared with the control group.

The basal levels of whole blood lactate in the control and magnesium sulfate-treated groups during forced swimming were shown in Figure 3. After swimming, the lactate levels increased to 190% (p<0.05)and 305% (p<0.01) of the basal Figure 4. The changes in blood levels of magnesium. Data are level in the magnesium sulfate-treated group and control group, presented as the mean ±SEM (n=6). *p<0.05 compared with respectively, and returned to the basal level at 30 min of basal levels; #p<0.05 compared with the control group. recovery. The lactate levels after swimming were attenuated at 115% in the magnesium sulfate-treated group (p<0.05) compared to those in the control group.

Table 1. Effects of magnesium sulfate, swimming, and magnesium sulfate+swimming on glucose, magnesium and GLUT-3 protein levels in the striatum. Data are the mean±SEM of four gerbils. C: saline control group; Mg: magnesium sulfate group; C+S: saline control plus short-term forced swimming group; Mg+S: magnesium sulfate plus short-term forced swimming group. C Mg C+S Mg+S Glucose 100.00±0.00 94.17±3.52 74.96±7.25 86.80±12.20 (% of control) Mg 100.00±0.00 105.71±0.42 105.96±2.22 104.51±3.72 (% of control) GLUT-3 relative expression level (%) 1.00±0.00 1.18±0.08 1.18±0.07 1.25±0.14

The results of this study indicate that forced swimming or an immediate increase in brain glucose concentrations. magnesium sulfate supplementation has no effect on the levels Therefore, the peripheral and central glucose concentrations of GLUT-3 protein, glucose and magnesium in the striatum, as may be elevated via regulation of the oxidation shown in Table 1. Swimming, pretreatment with magnesium phosphorylation, glycolysis pathways, and possibly other sulfate and magnesium sulfate plus swimming had no effect on mechanisms as well. Lactate production is generally GLUT-3 expression, or the glucose, and magnesium levels, considered to be the major cause of muscle fatigue and to have respectively. a positive influence on muscle contraction during exercise. Numerous studies have indicated that glucose and lactate Discussion levels are closely correlated with exercise intensity [22]. The results of this study indicate that forced swimming During a short term light- or moderate-intensity exercise, results in an increase in both whole blood glucose and lactate blood lactate remains at or very close to the basal levels. As levels, whereas pretreatment with magnesium sulfate increased the intensity of the exercise increases, a threshold is reached, glucose levels and attenuated lactate levels during forced beyond which blood lactate levels rise sharply [23,24]. It was swimming. Pretreatment with magnesium resulted in a also found that lactate accumulation in muscle cells until significant and immediate increase in whole blood glucose transporting out of the cell equals net production. This levels prior to exercise. This phenomenon was also observed in accumulation reflects a mismatch between the inefficient rapid our previous study [19]. The findings reported in that study production of ATP by glycogenolysis and the oxidative showed that pretreatment with magnesium sulfate resulted in processes that provide most of the net energy production over International Journal of Sport and Exercise Science, 1(2): 19-26 23

a contraction cycle [25]. This may alter glycolytic processes brain. and regulate glucose metabolism [22]. A number of reports In summary, a repeated blood-sampling assay was have suggested that lactate is involved in the significant shift developed for determining dynamic changes in whole blood from predominantly aerobic metabolism to predominantly glucose, lactate and magnesium concentrations in gerbils that anaerobic energy production [23]. Supplementation with had been subjected to short-term forced swimming. Forced magnesium may result in the attenuation of lactate levels under swimming resulted in an increase in blood glucose and lactate high-intensity swimming exercise and might provide an levels and magnesium sulfate supplementation resulted in additional energy source for enhancing exercise performance. enhanced glucose levels, but an attenuation effect on lactate Numerous studies have focused on the relation between levels. In addition, the possibility that short-term forced magnesium concentration and glucose levels during exercise. swimming exercise may be have given rise to shifts in In general, long-term or exhausting exercise induced magnesium to plasma compartments cannot be excluded, hypoglysaemia, hypomagnesaemia, while short-term and based on the findings reported herein. Moreover, magnesium high-intensity exercise induced hypermagnesaemia and supplementation had no effect on striatum GLUT-3 and hyperglycemia [9,10,26]. Our previous study demonstrated glucose levels in the forced swimming model. Further studies that short-term forced swimming resulted in an increase in will be required to investigate the effects of magnesium on both plasma glucose and magnesium levels [13]. However, the variations in GLUTs expression in different regions of the findings reported herein indicate that short-term forced brain. swimming increased whole blood glucose levels, but no Acknowledgments significant increase in whole blood magnesium levels was This study was supported by grants from the National found, as shown in Figs. 2 and 4. With respect to blood Science Council (NSC- 97-2113-M-468 -001 -), Taiwan, extracellular magnesium, various studies have indicated that R.O.C. short-term and high-intensity anaerobic exercise led to hypermagnesaemia as a consequence of a reduction in plasma References volume and a shift in cellular magnesium concentration [9,27]. Our previous data shown that in the short-term forced [1] Saris, N.E., Mervaala, E., Karppanen, H., Khawaja, J.A., & swimming resulted in an increase in plasma magnesium [13]; Lewenstam, A. (2000). Magnesium. An update on however, whole blood magnesium levels remained unchanged physiological, clinical and analytical aspects. Clinica Chimica in gerbil subjected the same short-term forced swimming Acta , 294 (1-2), 1-26. model in this study. A possible explanation for increased [2] Lukaski, H.C. (2000). Magnesium, zinc, and chromium plasma magnesium concentration during forced swimming nutriture and physical activity. The American Journal of events may elicit magnesium from red blood cells into plasma Clinical Nutrition , 72 (2 Suppl), 585S-593S. compartments. [3] Ebel, H., & Gunther, T. (1980). Magnesium metabolism: a On the other hand, our previous data indicated that review. Journal of Clinical Chemistry and Clinical magnesium sulfate and short-term forced swimming played a Biochemistry , 18 (5), 257-270. role in regulating cerebral glucose concentrations and magnesium sulfate led to an increase in glucose levels [19]. [4] Bohl, C.H., & Volpe, S.L. (2002). Magnesium and exercise. Moreover, for the intracellular uptake of glucose by Critical Reviews in Food Science and Nutrition , 42 (6), 533-63. insulin-sensitive cells, the translocation of GLUTs across the [5] Lukaski, H.C. (2001). Magnesium, zinc, and chromium plasma membrane is a vital step, in which insulin is induced by nutrition and athletic performance. Canadian Journal of autophophorylating beta subunits of insulin receptors after its Applied Physiology , 26, S13-22. specific binding. Magnesium acts in a stimulative manner in the step where insulin binds to its receptors and the [6] Nielsen, F.H., & Lukaski, H.C. (2006). Update on the autophophorylation of beta subunits. Intracellular magnesium relationship between magnesium and exercise. Magnesium stimulates intracellular glucose transport and its oxidation Research , 19 (3):180-189. [31,32]. We previously reported that short-term forced [7] Stendig-Lindberg, G., Shapiro, Y., Epstein, Y., Galun, E., swimming had no effect on GLUT-3 protein expression, Schonberger, E., Graff, E., & Wacker, W.E. (1987). Changes in glucose and magnesium levels in the cortex, whereas serum magnesium concentration after strenuous exercise. pretreatment with magnesium sulfate increased glucose and Journal of the American College of Nutrition , 6 (1), 35-40. magnesium levels in the cortex, and also resulted in an [8] Mooren, F.C., Golf, S.W., Lechtermann, A., & Volker, K. increased expression of GLUT-3 protein. The results of this (2005). Alterations of ionized Mg2+ in human blood after study indicate that forced swimming or magnesium sulfate exercise. Life Science ,77 (11), 1211-1225. supplementation has no effect on the levels of GLUT-3 protein, glucose and magnesium in the striatum, as shown in Table 1. [9] Rayssiguier, Y., Guezennec, C.Y., & Durlach, J. (1990). New These findings suggested that even the same exercise model experimental and clinical data on the relationship between and treatment with same dosage of magnesium may have magnesium and sport. Magnesium Research , 3 (2), 93-102. different effects on GLUT-3 protein expression, extracellular [10] Gotoh, M., Tajima, T., Suzuki, Y., Ikari, H., Iguchi, A., glucose and magnesium levels in the different regions of the Kakumu, S., & Hirooka, Y. (1990). Swimming stress that 24 International Journal of Sport and Exercise Science, Vol. 2. No.1 2010

causes hyperglycemia increases in vivo release of [22] Philp, A., Macdonald, A.L., & Watt, P.W. (2005). Lactate--a noradrenaline, but not acetylcholine, from the hypothalamus of signal coordinating cell and systemic function. The Journal of conscious rats. Brain Research , 780 (1), 74-79. Experimental Biology , 208 (Pt 24), 4561-4575.

[11] Poleszak, E., Wlaz, P., Szewczyk, B., Kedzierska, E., Wyska, [23] Davis, J.A., Frank, M.H., Whipp, B.J., & Wasserman, K. E., Librowski, T., Szymura-Oleksiak, J., Fidecka, S., Pilc, A., (1979). Anaerobic threshold alterations caused by endurance & Nowak, G. (2005). Enhancement of antidepressant-like training in middle-aged men. Journal of Applied Physiology , activity by joint administration of imipramine and magnesium 46 (6), 1039-1046. in the forced swim test: Behavioral and pharmacokinetic [24] Kindermann, W., Simon, G., & Keul, J. (1979). The studies in mice. Pharmacology, Biochemistry, and Behavior , 81 significance of the aerobic-anaerobic transition for the (3), 524-529. determination of work load intensities during endurance [12] Laires, M.J., & Alves, F. (1991). Changes in plasma, training. European Journal of Applied Physiology and erythrocyte, and urinary magnesium with prolonged swimming Occupational Physiology, 42 (1), 25-34. exercise. Magnesium Research , 4 (2):119-122. [25] Shulman, R.G. (2005). Glycogen turnover forms lactate during [13] Cheng, S.M., Yang, L.L., Chen, S.H., Hsu, M.H., Chen, I.J., & exercise. Exercise and Sport Sciences Reviews , 33 (4), Cheng, F.C. (2009). Magnesium sulfate enhances exercise 157-162. performance and manipulates dynamic changes in peripheral [26] Deuster, P.A., Dolev, E., & Kyle, S.B, (1987). Anderson RA, glucose utilization. European Journal of Applied Physiology , Schoomaker EB. Magnesium homeostasis during 108, 363-369. high-intensity anaerobic exercise in men. Journal of Applied [14] Vannucci, S.J., Maher, F., & Simpson, I.A. (1997). Glucose Physiology , 62 (2), 545-550. transporter proteins in brain: delivery of glucose to neurons and [27] Cordova, A. (1992). Changes on plasmatic and erythrocytic glia. Glia , 21 (1), 2-21. magnesium levels after high-intensity exercises in men. [15] Nagamatsu, S., Kornhauser, J.M., Burant, C.F., Seino, S., Mayo, Physiology & Behavior , 52 (4):819-821. K.E., & Bell, G.I. (1992). Glucose transporter expression in [28] Altura, B.T., Shirey, T.L., Young, C.C., Dell'Orfano, K., Hiti, J., brain. cDNA sequence of mouse GLUT3, the brain facilitative Welsh, R., Yeh, Q., Barbour, R.L., & Altura, B.M. (1994). glucose transporter isoform, and identification of sites of Characterization of a new ion selective electrode for ionized expression by in situ hybridization. The Journal of Biological magnesium in whole blood, plasma, serum, and aqueous Chemistry, 267 (1), 467-472. samples. Scandinavian Journal of Clinical and Laboratory [16] Maher, F., Vannucci, S.J., & Simpson, I.A. (1994). Glucose Investigation Supplementum , 217, 21-36. transporter proteins in brain. The FASEB Journal: Official [29] Altura, B.T., Shirey, T.L., Young, C.C., Hiti, J., Dell'Orfano, K., Publication of the Federation of American Societies for Handwerker, S.M., & Altura, B.M. (1992). A new method for Experimental Biology , 8 (13), 1003-1011. the rapid determination of ionized Mg2+ in whole blood, serum [17] Joost, H.G., & Thorens, B. (2001). The extended GLUT-family and plasma. Methods and Findings in Experimental and of sugar/polyol transport facilitators: nomenclature, sequence Clinical Pharmacology , 14 (4), 297-304. characteristics, and potential function of its novel members [30] Resnick, L.M., Altura, B.T., Gupta, R.K., Laragh, J.H., (review). Molecular Membrane Biology , 18 (4), 247-256. Alderman, M.H., & Altura, B.M. (1993). Intracellular and [18] Chen, I.J., & Cheng, S.M. (2009). Magnesium sulfate enhances extracellular magnesium depletion in type 2 glucose transporter-3 expression in gerbils subjected to (non-insulin-dependent) diabetes mellitus. Diabetologia, 36 (8), short-term forced swimming. International Journal of Sport 767-770. and Exercise Science , 1 (3), 75-80. [31] Paolisso, G., Scheen, A., D'Onofrio, F., & Lefebvre, P. (1990). [19] Cheng, S.M., Yang, D.Y., Lee, C.P., Pan, H.C., Lin, M.T., Chen, Magnesium and glucose homeostasis. Diabetologia , 33 (9), S.H., & Cheng, F.C. (2007). Effects of magnesium sulfate on 511-514. dynamic changes of brain glucose and its metabolites during a [32] Paolisso, G., & Barbagallo, M. (1997). Hypertension, diabetes short-term forced swimming in gerbils. European Journal of mellitus, and insulin resistance: the role of intracellular Applied Physiology , 99 (6), 695-699. magnesium. American Journal of Hypertension , 10 (3), [20] Pisani, A., Bonsi, P., Picconi, B., Tolu, M., Giacomini, P., & 346-355. Scarnati, E. (2001). Role of tonically-active neurons in the

control of striatal function: cellular mechanisms and behavioral AUTHORS BIOGRAPHY correlates. Progress in Neuro-Psychopharmacology & Biological Psychiatry , 25 (1), 211-230.

[21] Harms, P.G., & Ojeda, S.R. (1974). A rapid and simple procedure for chronic cannulation of the rat jugular vein. Journal of Applied Physiology , 36 (3), 391-392. International Journal of Sport and Exercise Science, 1(2): 19-26 25

I-Ju Chen Shiu-Min Cheng Employment Employment Assistant professor, Department of Assistant professor, Department of Physical Edu ction, Asia University, Psychology, Asia University, Taiwan Taiwan. Degree Degree PhD Master Research interests Research interests Exercise physiology and neuroscience Exercise physiology E-mail: [email protected] E-mail: [email protected]