Cell-specific expression of plasma membrane calcium ATPase isoforms in retinal neurons.
Ca(2+) extrusion by high-affinity plasma membrane calcium ATPases (PMCAs) is a principal mechanism for the clearance of Ca(2+) from the cytosol. The PMCA family consists of four isoforms (PMCA1-4). Little is known about the selective expression of these isoforms in brain tissues or about the physiological function conferred upon neurons by any given isoform. We investigated the cellular and subcellular distribution of PMCA isoforms in a mammalian retina. Mouse photoreceptors, cone bipolar cells and horizontal cells, which respond to light with a graded polarization, express isoform 1 (PMCA1) of the PMCA family. PMCA2 is localized to rod bipolar cells, horizontal cells, amacrine cells, and ganglion cells, and PMCA3 is predominantly expressed in spiking neurons, including both amacrine and ganglion cells but is also found in horizontal cells. PMCA4 was found to be selectively expressed in both synaptic layers. Optical measurements of Ca(2+) clearance showed that PMCAs mediate Ca(2+) extrusion in both rod and cone bipolar cells. In addition, we found that rod bipolar cells, but not cone bipolar cells possess a prominent Na(+)/Ca(2+) exchange mechanism. We conclude that PMCA isoforms are selectively expressed in retinal neurons and that processes of Ca(2+) clearance are different in rod and cone bipolar cells.
Krizaj
David
D
Department of Physiology, University of California San Francisco, San Francisco, California 94143-0730, USA. krizaj@phy.ucsf.edu
Demarco
Steven J
SJ
Johnson
Juliette
J
Strehler
Emanuel E
EE
Copenhagen
David R
DR
D025042:Amacrine Cells / Q000201:enzymology; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000201:enzymology*; D008322:Mammals; D051379:Mice; D008810:Mice, Inbred C57BL; D053499:Plasma Membrane Calcium-Transporting ATPases; D012160:Retina / Q000166:cytology / Q000201:enzymology*; D017949:Retinal Cone Photoreceptor Cells / Q000201:enzymology; D012165:Retinal Ganglion Cells / Q000201:enzymology; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
D027682:Cation Transport Proteins; D019831:Sodium-Calcium Exchanger; D053499:Plasma Membrane Calcium-Transporting ATPases; C506954:Atp2b1 protein, mouse; C506959:Atp2b2 protein, mouse; D000252:Calcium-Transporting ATPases