Moreover, weaker signals were mentioned in inner segments of photoreceptors and cell body of bipolar and horizontal cells. cells, but not cone bipolar cells possess a prominent Na+/Ca2+ exchange mechanism. We conclude that Albaspidin AP PMCA isoforms are selectively indicated in retinal neurons and that processes of Ca2+ clearance are different in pole and cone bipolar cells. strong class=”kwd-title” Indexing terms: PMCA, Ca2+ extrusion, photoreceptor, bipolar cell, Na/Ca exchange Ca2+ functions as a critical and ubiquitous second messenger by regulating a variety of key intracellular processes (Berridge et al., 2000). The concentration of free intracellular Ca2+ ions, [Ca2+]i, is set by the balance between Ca2+ access into the cytoplasm and Ca2+ removal by means of buffering proteins, uptake into intracellular organelles and extrusion across the plasma membrane. Together with Na+/Ca2+ exchangers (NCXs), the plasma membrane calcium ATPases (PMCAs) are the principal mechanism for Ca2+ extrusion from most vertebrate cells. The mammalian PMCA family is definitely encoded Albaspidin AP by four genes whose protein products have been designated PMCA1C4 (examined in Guerini and Carafoli, 1998; Strehler and Zacharias, 2001). Expression studies in heterologous cell systems have revealed Albaspidin AP the members of the family differ significantly in their affinities for Ca2+ and calmodulin and are linked in a different way to multiprotein complexes comprising PDZ website proteins (Enyedi et al., 1994; DeMarco and Strehler, 2001; Caride et al., 2001b). PMCA isoforms also are differentially controlled by intracellular messengers such as protein kinases A and C, proteases, and acidic phospholipids (examined by Monteith and Roufogalis, 1995; Penniston and Enyedi, 1998; Strehler and Zacharias, 2001). However, immunolocalization of PMCA isoforms to different neuron subtypes within a cells offers hitherto been seldom carried out (de Talamoni et al., 1993; Dumont et al., 2001). Moreover, the functional significance of differential localization of the PMCA isoforms to central nervous system (CNS) cells and to different cell types is definitely poorly recognized. The vertebrate retina consists of cell types with different light response properties. Some classes of retinal neurons signal with graded potentials (photoreceptors, Albaspidin AP horizontal and bipolar cells), others communicate by means of action potentials (ganglion cells), and still others use both graded and action potentials (amacrine cells; Werblin and Dowling, 1969; Kolb, 1995; Bieda and Copenhagen, 1999). Spiking induces transient elevations in [Ca2+]i compared with the sustained elevations in nonspiking, graded potential neurons. PRL Bipolar, amacrine, and ganglion cells can be further divided into ON and OFF subclasses, which respond to light with depolarization and hyperpolarization, respectively (Werblin and Dowling, 1969). These variations in light-evoked reactions presumably place very different demands within the calcium rules systems of different classes of retinal neuron. In this study, we examine the hypothesis that functionally highly varied populations of retinal neuron rely on different Ca2+ extrusion mechanisms. By using electrophysiological methods and optical imaging techniques, Ca2+ extrusion from photoreceptor terminals in tiger salamander and tree shrew was shown to be specifically mediated by a PMCA-like mechanism (Krizaj and Copenhagen, 1998; Morgans et al., 1998). In contrast, a Na+/K+,Ca2+ exchanger mechanism mediates Ca2+ extrusion from photoreceptor outer segments, suggesting that Ca2+ clearance is definitely highly compartmentalized in different regions of the same cell (Miller et al., 1994; Krizaj and Copenhagen, 1998). The localization of PMCAs to synaptic terminals of rods and cones was confirmed by immunohistochemistry by using a pan-specific PMCA antibody (Morgans et al., 1998; Krizaj and Copenhagen, 1998). However, it is not known which particular PMCA isoforms are indicated in photoreceptors. The mechanisms of Ca2+ extrusion from bipolar cells are currently unclear. In one study, Ca2+ efflux from synaptic terminals of teleost bipolar cells was shown to be mediated specifically by PMCA-like extrusion mechanisms (Zenisek and Matthews, 2000). However, Kobayashi and Tachibana (1995) found evidence for Na+/Ca2+ exchanger-mediated Ca2+ extrusion from these same type of fish bipolar cells. No info is definitely available about Ca2+ extrusion systems used in mammalian bipolar cells. PMCA-mediated Ca2+ efflux also contributes to Ca2+ extrusion from third-order retinal neurons (Gleason et al., 1994, 1995). In cultured chick amacrine cells, PMCAs contribute from ~0 to ~50% of total Ca2+ clearance (Gleason et al.,.