Ontogeny of plasma membrane Ca²⁺ ATPase isoforms in the neural retina of the postnatal rat

Calcium ion (Ca²⁺) signaling has been widely implicated in developmental events in the retina, but little is known about the specific mechanisms utilized by developing neurons to decrease intracellular Ca ²⁺. Using immunocytochemistry, we determined the expression profiles of all known isoforms of a key Ca²⁺ transporter, the plasma membrane Ca²⁺ ATPase (PMCA), in the rat retina. During the first postnatal week, the four PMCA isoforms were expressed in patterns that differed from their expression in the adult retina. At birth, PMCA1 was found in the ventricular zone and nascent cell processes in the distal retina as well as in ganglion and amacrine cells. After the first postnatal week, PMCA1 became restricted to photoreceptors and cone bipolar cells. By P10 (by postnatal day 10), most inner retinal PMCA consisted of PMCA2 and PMCA3. Prominent PMCA4 expression appeared after the first postnatal week and was confined primarily to the ON sublamina of the inner plexiform layer (IPL). The four PMCA isoforms could play distinct functional roles in the development of the mammalian retina even before synaptic circuits are established. Their expression patterns are consistent with the hypothesis that inner and outer retinal neurons have different Ca²⁺ handling needs.