title: Expression of calcium transporters in the retina of the tiger salamander (Ambystoma tigrinum).
abstract: Changes in intracellular calcium concentration, [Ca2+]i, modulate the flow of visual signals across all stages of processing in the retina, yet the identities of Ca2+ transporters responsible for these changes are still largely unknown. In the current study, the distribution of plasma membrane and intracellular Ca2+ 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 Ca2+ 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+/Ca2+ exchangers, a high-capacity Ca2+ extrusion system, were expressed in the outer plexiform layer and in a subset of inner nuclear and ganglion layer cells. Intracellular Ca2+ store transporters were also represented prominently. SERCA2a, a splice variant of the sarcoplasmic-endoplasmic Ca2+ 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) Ca2+ channels in the salamander retina are represented by the isoform 2 of the IP3 receptor family and the isoform 2 of the ryanodine receptor family. These results indicate that Ca2+ transporters in the salamander retina are expressed in a cell type-specific manner.
authors.affiliation: Department of Ophthalmology, University of California, San Francisco, School of Medicine, San Francisco, California 94143-0730, USA. krizaj@phy.ucsf.edu
authors.forename: David
authors.initials: D
authors.lastname: Krizaj
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Liu
authors.forename: David R
authors.initials: DR
authors.lastname: Copenhagen
mesh_terms: D000557:Ambystoma / Q000033:anatomy & histology / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D015220:Calcium Channels / Q000096:biosynthesis*; D000252:Calcium-Transporting ATPases / Q000096:biosynthesis*; D002462:Cell Membrane / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D007424:Intracellular Fluid / Q000378:metabolism; D007527:Isoenzymes / Q000096:biosynthesis; D018613:Microscopy, Confocal; D010786:Photoreceptor Cells / Q000033:anatomy & histology / Q000502:physiology; D012160:Retina / Q000033:anatomy & histology / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000096:biosynthesis*
chemical_list: D015220:Calcium Channels; D007527:Isoenzymes; D019831:Sodium-Calcium Exchanger; D000252:Calcium-Transporting ATPases