Expression of calcium transporters in the retina of the tiger salamander ( Ambystoma tigrinum )

Changes in intracellular calcium concentration, [Ca 2+ ]i, modulate the flow of visual signals across all stages of processing in the retina, yet the identities of Ca 2+ transporters responsible for these changes are still largely unknown. In the current study, the distribution of plasma membrane and intracellular Ca 2+ transporters in the retina of tiger salamander, a model system for physiological studies of retinal function, was determined. Plasma membrane calcium ATPases (PMCAs), responsible for high‐affinity Ca 2+ extrusion, were highly expressed in the salamander retina. PMCA isoforms 1, 2, and 4 were localized to photoreceptors, whereas the inner retina expressed all four isoforms. PMCA3 was expressed in a sparse population of amacrine and ganglion neurons, whereas PMCA2 was expressed in most amacrine and ganglion cells. Na + /Ca 2+ exchangers, a high‐capacity Ca 2+ extrusion system, were expressed in the outer plexiform layer and in a subset of inner nuclear and ganglion layer cells. Intracellular Ca 2+ store transporters were also represented prominently. SERCA2a, a splice variant of the sarcoplasmic‐endoplasmic Ca 2+ ATPase, was found mostly in photoreceptors, whereas SERCA2b was found in the majority of retinal neurons and in glial cells. The predominant endoplasmic reticulum (ER) Ca 2+ channels in the salamander retina are represented by the isoform 2 of the IP 3 receptor family and the isoform 2 of the ryanodine receptor family. These results indicate that Ca 2+ transporters in the salamander retina are expressed in a cell type‐specific manner. J. Comp. Neurol. 475:463–480, 2004. © 2004 Wiley‐Liss, Inc.