Comparative Biochemistry and Physiology, Part A 147 (2007) 779–787 www.elsevier.com/locate/cbpa Review Calcium signaling in lizard red blood cells ☆ ⁎ Piero Bagnaresi a, Miguel T. Rodrigues b, Célia R.S. Garcia a, a Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil b Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil Received 9 May 2006; received in revised form 21 September 2006; accepted 25 September 2006 Available online 3 October 2006 Abstract The ion calcium is a ubiquitous second messenger, present in all eukaryotic cells. It modulates a vast number of cellular events, such as cell division and differentiation, fertilization, cell volume, decodification of external stimuli. To process this variety of information, the cells display a number of calcium pools, which are capable of mobilization for signaling purposes. Here we review the calcium signaling on lizards red blood cells, an interesting model that has been receiving an increasing notice recently. These cells possess a complex machinery to regulate calcium, and display calcium responses to extracellular agonists. Interestingly, the pattern of calcium handling and response are divergent in different lizard families, which enforces the morphological data to their phylogenetic classification, and suggest the radiation of different calcium signaling models in lizards evolution. © 2006 Elsevier Inc. All rights reserved. 2+ Keywords: Ca homeostasis; Red blood cells; Lizards; IP3 receptors; Ryanodine receptors; Purinoceptors; Intracellular messengers Contents 1. Calcium handling mechanisms in lizards' RBCs ........................................... 781 2. Acidic pools ............................................................. 782 3. Participation of mitochondria in calcium homeostasis in lizards, RBCs . ............................ 784 4. Purinoceptors: perceiving extracellular messages .......................................... 784 5. Second messengers in RBC calcium signaling ............................................ 785 Acknowledgements ............................................................ 785 References ................................................................. 785 Understanding the basic mechanism of Ca2+ homeostasis and variety of physiological events requiring changes in intracellular role of the different organelles, at rest and during cell stim- Ca2+ concentration. In this review we will deal primarily with ulation, is a prerequisite to understand the modulation of a large the mechanism of Ca2+ handling in the red blood cells (RBCs) of lizards, an interesting model system that has received much ☆ attention over the last years by comparative physiologists. This paper is part of the 3rd special issue of CBP dedicated to The Face of 2+ Latin American Comparative Biochemistry and Physiology organized by Before entering a detailed description of Ca homeostasis in Marcelo Hermes-Lima (Brazil) and co-edited by Carlos Navas (Brazil), Rene lizard RBCs, we summarize a few general concepts, primarily Beleboni (Brazil), Rodrigo Stabeli (Brazil), Tania Zenteno-Savín (Mexico) and derived from work on mammalian cells. By necessity this the editors of CBP. This issue is dedicated to the memory of two exceptional summary is incomplete and the interested reader is referred to the men, Peter L. Lutz, one of the pioneers of comparative and integrative numerous recent reviews published on the topic (Rizzuto and physiology, and Cicero Lima, journalist, science lover and Hermes-Lima's dad. ⁎ Corresponding author. Rua do Matão, travessa 14, 321. CEP 05508-900 São Pozzan, 2006). Paulo, SP, Brazil. Tel./fax: +55 11 30917518. All eukaryotic cells display several mechanisms to control and E-mail address: [email protected] (C.R.S. Garcia). operate calcium, maintaining an important difference between 1095-6433/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.cbpa.2006.09.015 780 P. Bagnaresi et al. / Comparative Biochemistry and Physiology, Part A 147 (2007) 779–787 extra and intracellular calcium concentrations (Fig. 1). Those binds to different protein targets), parvalbumin, calbindin and concentrations differ by over 4 orders of magnitude, i.e. around calretinin (Baimbridge et al., 1992). 10− 7 M/10− 8 M in the cytosol and 10− 3 M/10− 2 Minthe Ca2+ entry into the cells is mediated by a variety of channels extracellular medium. It has been suggested that very early on in the plasma membrane which can be grouped according to their during evolution cells developed mechanisms to keep the cyto- gating mechanism, as follows: 1 — voltage-operated channels, solic Ca2+ concentrations lower than in the extracellular medium activated by membrane depolarization (Mori et al., 1993); 2 — because Ca2+ has the tendency to form insoluble precipitates with receptor-operated channels which open in response to binding of phosphate, which is very abundant in the cytosol. Indeed, the the agonists; and 3 — second messenger-operated channels, other most abundant divalent cation, Mg2+, is not regulated at which open in response to the change in concentration of a very different levels inside and outside the cell (1 mM) possibly second messenger within the cells (e.g. cyclic nucleotides, because it does not form insoluble complexes with phosphate in diacylglicerol, etc) and finally 4 — a still largely mysterious the physiological concentration range. group of channels, operationally defined as store-operated chan- In order to maintain the Ca2+ gradient across the plasma nels, that open in response to a decrease of Ca2+ within the membrane, cells have developed several mechanisms to extrude endoplasmic reticulum with a mechanism called capacitative Ca2+ from the cytosol such as the plasma membrane Ca2+ calcium entry (Putney and Bird, 1994). The molecular mecha- ATPases (PMCA), which actively pump Ca2+ out across the nism of regulation of these channels is still unknown. plasma membrane at the expense of ATP hydrolysis and the Na+/ The endoplasmic reticulum plays a central role in the man- Ca2+ (and the Na+/K+) exchangers, antiporters that exchange agement of calcium in eukaryotic cells, being involved in the Ca2+ at the expense of the gradients of monovalent ions and of transient release and re-uptake of Ca2+ (Meldolesi and Pozzan, the membrane potential (they are in fact electrogenic, 3Na+/Ca2+). 1998a,b). This organelle is a network of interlinked membranous The PMCAs are known to be regulated not only by Ca2+ concen- tubules and cisternae, spread throughout the cell (Park et al., tration, but also by the Ca2+-binding protein, calmodulin (Carafoli 2000). A sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) et al., 1996). pumps Ca2+ into the ER lumen utilizing the energy derived Within the cytosol, several proteins act as Ca2+ buffers. The from ATP hydrolysis. The enzyme is highly conserved among best known among these cytosolic Ca2+ buffers are: calmodulin species and its cycle has been extensively studied since 1970 (which also controls a multitude of biological processes when it (see Wolosker and de Meis, 1995). Like the PMCA, the SERCA Fig. 1. Calcium handling mechanisms present in eukaryotic cells. The red rectangle represents the mitochondrion, the green oval represents the endoplasmic reticulum, and the yellow hexagon represents an acidic pool. On the plasma membrane, PMCA, Na+/Ca2+ exchanger, a calcium channel and a GPCR, responsible for cellular 2+ stimulus. In the ER, SERCA pumps calcium to the lumen of the organelle, and this store can be mobilized by IP3 or ryanodine receptors. In the mitochondrion, Ca uniporter and RaM are responsible for the filling of the store. In the acidic pools, the H+ gradient are required to calcium storage. Calcium can be mobilized from internal stores by second messengers like IP3, for example, generated by phospholipase C (PLC) activation via G-protein-coupled receptors (GPCR). P. Bagnaresi et al. / Comparative Biochemistry and Physiology, Part A 147 (2007) 779–787 781 2+ pump has a phosphorylated, acyl-phosphate acid-stable inter- inhibit the channel. This Ca dependence of IP3 receptors is mediate (E-P) in its cycle (Mathiasen et al., 1993). important for the generation of temporal oscillations and pro- A higher density of the SERCA pump was one of the pagating waves (Berridge et al., 1988; Berridge, 1990; Petersen solutions found during evolution to keep up with requirements and Wakui, 1990; Tsien and Tsien, 1990; Berridge and Moreton, for a higher rate of Ca2+ cycling into and out of the sarcoplasmic 1991; Meyer, 1991, Thomas et al., 1996; Weissman et al., 2004, reticulum of certain types of muscles which operate at high Isshiki et al., 2004; Stuyvers et al., 2005). A recently reported frequency. One such muscle is found in sonic fibers of the toafish new indicator will certainly lead to advances in understanding 2+ 2+ swimbladder, where Ca uptake by SERCA is 50-fold greater the role of repetitive Ca spikes. A modified version of IP3 that than in red fibers (Davis et al., 1997). Another example may be is membrane permeant and photoactivatable is able to elicit the found in the special noise-making muscles rattlesnakes use to release of intracellular Ca2+ pools in a controlled process warn off predators. The rate at which these muscles function (Li et al., 1998). The authors concluded that cells might decode indicates that they might possess features in common with the Ca2+ signaling by the activation of gene expression. toadfish