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Calcium gradients and light-evoked calcium changes outside rods in the intact cat retina

Published online by Cambridge University Press:  02 June 2009

Ron P. Gallemore ,
Jian-Dong Li ,
Victor I. Govardovskii  and
Roy H. Steinberg
Ron P. Gallemore
Affiliation:
Departments of Physiology and Ophthalmology, University of California, San Francisco
Jian-Dong Li
Affiliation:
Departments of Physiology and Ophthalmology, University of California, San Francisco
Victor I. Govardovskii
Affiliation:
Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Russia
Roy H. Steinberg
Affiliation:
Departments of Physiology and Ophthalmology, University of California, San Francisco
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Abstract

We have studied light-evoked changes in extracellular Ca2+ concentration in the intact cat eye using ion-sensitive double-barreled microelectrodes. Two prominent changes in Ca2+ concentration were observed that differed in retinal location. There was a light-evoked increase in accompanied by brief ON and OFF transients, which was maximal in the inner plexiform layer and was not further studied. There was an unexpected sustained light-evoked decrease in of relatively rapid onset and offset, which was maximal in the distalmost region of the subretinal space (SRS). in the SRS was 1.0 mM higher than in the vitreous humor during dark adaptation and this transretinal gradient disappeared during rod-saturating illumination. After correcting for the light-evoked increase in the volume of the SRS, an increase in the total Ca2+ content of the SRS during illumination was revealed, which presumably represents the Ca2+ released by rods. To explain the light-evoked changes, we used the diffusion model described in the accompanying paper (Li et al., 1994b), with the addition of light-dependent sources of Ca2+ at the retina/retinal pigment epithelium (RPE) border and rod outer segments. We conclude that a drop in around photoreceptors, which persists during illumination and reduces a transretinal Ca2+ gradient, is the combined effect of the light-evoked SRS volume increase, Ca2+ release from photoreceptors, and an unidentified mechanism(s), which is presumably Ca2+ transport by the RPE. The relatively rapid onset and offset of the decrease remains unexplained. These steady-state shifts in should have significant effects on photoreceptor function, especially adaptation.

Keywords

CalciumCatPhotoreceptor(s)Subretinal spaceExtracellular volume
Type
Research Articles
Information
Visual Neuroscience , Volume 11 , Issue 4 , July 1994 , pp. 753 - 761
Copyright
Copyright © Cambridge University Press 1994

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