J Physiol Sci (2009) 59:23–29 DOI 10.1007/s12576-008-0001-y ORIGINAL PAPER Gastric acid secretion in cholecystokinin-1 receptor, -2 receptor, and -1, -2 receptor gene knockout mice Setsuko Kanai Æ Hiroko Hosoya Æ Saeko Akimoto Æ Minoru Ohta Æ Toshimitsu Matsui Æ Soichi Takiguchi Æ Akihiro Funakoshi Æ Kyoko Miyasaka Received: 6 June 2007 / Accepted: 26 September 2008 / Published online: 30 November 2008 Ó The Physiological Society of Japan and Springer 2008 Abstract Gastrin is important for stimulating acid secre- was impaired in mice without CCK-2R. The interaction of tion as well as differentiating gastric mucosal cells via histamine and carbachol was conserved in all genotypes. In cholecystokinin-2 receptors (CCK-2Rs). In turn, CCK acts conclusion, CCK-2R is necessary to respond to carbachol as preferably via CCK-1R to release somatostatin, and well as to produce the maximal acid secretion, while the role somatostatin has been postulated to exhibit a tonic inhibition of CCK-1R in acid secretion is less important. of gastrin bioactivity. The present study was designed to examine the hypothesis that CCK-1R and 2R may act in Keywords Acetylcholine Á CCK Á Knockout Á Mice opposite directions in gastric acid secretion. Having gener- ated CCK-1R(-/-), 2R(-/-), and 1R(-/-)2R(-/-) mice, we examined the regulation of gastric acid secretion in four Introduction genotypes including wild-type mice. Parietal cells possess histamine receptors, muscarinic receptors, and CCK-2Rs. Gastric acid secretion is regulated in a complex manner by Since histamine increases cAMP and carbachol increases neurocrine, endocrine, and paracrine signals. The primary calcium, the responses of gastric acid secretion to graded source of gastric acid is the parietal cells, and the major doses of histamine, carbachol, and a combination of hista- peripheral stimuli acting on the parietal cells directly are mine ? carbachol were determined. The sensitivity to histamine, acetylcholine, and gastrin [1]. Gastrin has been histamine did not differ among the four genotypes, while the reported to stimulate acid secretion in two ways via gastrin/ maximal acid secretion was lower in CCK-2R(-/-) mice cholecystokinin-2 receptors (CCK-2Rs): (1) by acting on than in wild-type mice. In addition, sensitivity to carbachol the enterochromaffin-like (ECL) cells to stimulate hista- mine release and de novo formation of histamine, and (2) by acting directly on the parietal cells to stimulate acid S. Kanai (&) Á H. Hosoya Á S. Akimoto Á M. Ohta Á K. Miyasaka secretion [2, 3], although this latter effect is still contro- Department of Clinical Physiology, versial. The parietal cells possess three different types of Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, receptors: CCK-2R, muscarinic 3 receptor (M3-R), and Itabashi-ku, Tokyo 173-0015, Japan histamine 2 receptor (H2-R). Two cellular pathways of acid e-mail: [email protected] secretion in the parietal cells have been elucidated: T. Matsui increases in cAMP content and increases in calcium con- Department of Medicine, Kobe University School of Medicine, centration. Histamine activates H2-Rs and increases cAMP Kobe 650-0017, Japan in the parietal cells, resulting in gastric acid secretion. S. Takiguchi Gastrin and acetylcholine released from parasympathetic Division of Clinical Research, National Kyushu Cancer Center, nerve terminals activate CCK-2R and M3-R, respectively, Fukuoka 811-1395, Japan increase calcium concentrations in the parietal cells, and stimulate acid secretion [1, 2]. A. Funakoshi Department of Gastroenterology, However, in a recent report [4] using L-histidine decar- National Kyushu Cancer Center, Fukuoka 811-1395, Japan boxylase (HDC)-deficient (-/-) mice, which could not 123 24 J Physiol Sci (2009) 59:23–29 synthesize histamine in the ECL cells, gastrin failed to seven generations. Three male CCK-1R(-/-) mice were stimulate acid secretion. Moreover, neither histamine nor bred with 12 female CCK-2R(-/-) mice to yield F1 gastrin stimulated gastric acid secretion in H2-R (-/-) progeny with the genotype CCK-1R(?/-)2R (?/-). Male mice [5]. This evidence indicates that histamine is a final and female F1 mice were then bred to yield progeny with mediator of acid secretion in mice when gastrin is admin- nine genotypes: CCK-1R(?/?)2R(?/?), CCK-1R(?/ istered. On the other hand, gastrin is known to be more ?)2R(?/-), CCK-1R(?/?)2R(-/-), CCK-1R(?/-)2R important for the differentiation of gastric mucosal cells (?/?), CCK-1R(?/-)2R(?/-), CCK-1R(?/-)2R(-/-), than for the acid secretion in mice [6, 7]. CCK-2R (-/-) CCK-1R(-/-)2R(?/?), CCK-1R(-/-)2R(?/-) and mice showed a decrease in the numbers of parietal cells and CCK-1R(-/-)2R(-/-). Finally, male CCK-1R(-/-) ECL cells, and sustained hypergastrinemia [8, 9]. The 2R(-/-) mice were then bred with female CCK-1R(-/-) numbers in gastrin-producing G cells were increased and 2R(-/-) mice to obtain double knockout mice. CCK- the decrease in antral D cell numbers was observed as 1R(-/-) and CCK-2R(-/-) mice were selected from the possibly due to the long-term elevation of gastric pH [8]. above lines, and wild-type mice CCK-1R(?/?)2R(?/?) More recently, Chen et al. [10] reported that differentiation were selected at random from both the CCK-1R and CCK- of gastric ECL cells is altered in CCK-2R (-/-) mice: ECL 2R lines [17–19]. Female mice at 6–8 months of age were cells were replaced by an ‘‘ECL-like’’ cell type, character- used for the present experiments. The animals were main- ized by a lack of secretory vesicles, and the histamine tained in individual cages in an air-conditioned room at content and HDC activity in the oxyntic mucosa were low. 21°C, with 55 ?/- 5% humidity, and with a 12 h light/dark In turn, somatostatin was postulated to exhibit a tonic photocycle (8:00AM–20:00PM) at Tokyo Metropolitan inhibition of parietal cells, ECL cells, and G cells in dogs. Institute of Gerontology. The cage size was 18 9 Canine somatostatin-producing D-cells possess CCK-1R 30 9 11 cm. [11], and CCK acts preferably via CCK-1R to release somatostatin [12]. We reported overexpression of CCK-2R Materials and chemicals in CCK-1R deficient (OLETF) rats [13]. Tachibana et al. [14] reported in the OLETF rats that CCK produced higher Xylazine and ketamine were purchased from Wako Pure gastric acid secretion compared with control rats. These Chemical Industries, Ltd. (Tokyo, Japan), histamine and observations suggest that CCK-1R and 2R may act in carbamylcholine (carbachol) from Sigma Chemical Co. (St opposite directions in gastric acid secretion. Two types of Louis, MO, USA), and somatostatin-14 from Peptide CCK receptors (CCKAR and CCK-BR) have been cloned Institute, Inc. (Osaka, Japan). [15], and recently renamed CCK-1R and CCK-2R [16]. CCK-1R binds sulfated CCK with 500- to 1,000-fold Experimental protocols higher affinity than gastrin and non-sulfated CCK, while CCK-2R interacts with gastrin and CCK with almost the The mice fasted overnight, but had free access to water. same affinity. Recently, we generated CCK-1R(-/-), After anesthetization by a mixture of xylazine and ketamine 2R(-/-), and 1R(-/-)2R(-/-) mice [17–19]. Here, the (11.3 and 8.7 mg/kg in, respectively), the trachea was role of CCK-1R and 2R in gastric acid secretion was cannulated. An overhead lamp was used to maintain core determined using these three genotypes of mice as well as body temperature at 36*38°C. The abdomen was opened wild-type mice. and the esophagus and pylorus were ligated. PE-50 tubing 0.58 mm inner diameter (ID), 0.965 mm outer diameter (OD) was inserted through an incision in the forestomach to Materials and methods infuse isotonic saline. Vinyl tubing (2.0 mm ID, 2.8 mm OD) was inserted in the antrum to collect stomach secretions The present experimental protocol was reviewed and [4]. After washing with 6–8 ml isotonic saline (37°C), an approved by the appropriate committee of the Tokyo isotonic saline infusion was started at a rate of 0.2 ml/min. Metropolitan Institute of Gerontology. We also followed In some animals, the right femoral vein was cannulated the Guiding Principles for the Care and Use of Laboratory to infuse somatostatin-14. Animals approved by The Japanese Pharmacological Society. Responses to graded doses of carbachol Animals Samples were collected every 10 min, and acid output (lmol H?) was determined by titration using an autotitrator The progenitor strain for CCK-1R(-/-) and 2R(-/-) mice (TOA Electronics Ltd., Tokyo, Japan). After 60 min basal was C57BL/6J. Backcrossing was carried out for more than collection, carbachol (10, 50, and 100 lg/kg) was injected 123 J Physiol Sci (2009) 59:23–29 25 subcutaneously in wild-type, CCK-1R(-/-), 2R(-/-), 1R(-/-), 24.28 ± 0.34 g for CCK-2R(-/-), and and 1R(-/-)2R(-/-) mice. Samples were collected sub- 23.23 ± 0.35 g for CCK-1R(-/-)2R(-/-) mice. There sequently for an additional 60 min. were no significant differences among genotypes. We found slight differences in acid secretion in response to carbachol between CCK-2R(-/-) and CCK-1R(-/-) Basal gastric acid secretion among four genotypes 2R(-/-) mice. No dose of carbachol produced a signifi- cant increase in acid secretion in CCK-2R(-/-) mice; The basal secretion level was estimated using the mean however, CCK-1R(-/-)2R(-/-) mice responded to 50 value during the 30 min before injection obtained from all and 100 lg/kg carbachol, producing significant increases. experiments. When analyzed by one-way ANOVA, the Based upon a previous report [11] that CCK-1Rs are basal gastric acid secretion was significantly different located in somatostatin-secreting cells of the stomach, we among the four genotypes [F(3,241) = 7.071, P = 0.0001] examined whether somatostatin could inhibit the sub- (Table 1).