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  • The determination of total cGMP levels in rod outer segments from intact toad photoreceptors in response to light superimposed on background and to consecutive flashes: A second light flash accelerates the dark recovery rate of cGMP levels in control media, but not in Na+-free, low Ca2+ medium

Visual Neuroscience

Table of Contents - 1993 - Volume 10, Issue 01  

Research Articles

The determination of total cGMP levels in rod outer segments from intact toad photoreceptors in response to light superimposed on background and to consecutive flashes: A second light flash accelerates the dark recovery rate of cGMP levels in control media, but not in Na+-free, low Ca2+ medium

Adolph I. Cohena1 and Christine Blazynskia1

a1 Departments of Biochemistry and Molecular Biophysics and Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis

Abstract

In previous experiments we established that a light flash reduced cGMP levels of toad rod outer segments within the transduction time interval, but that recovery of the dark level of cGMP occurred more slowly than reported electrophysiological recovery of membrane potential. We now report that a second light flash accelerates the recovery rate of total cGMP following an initial flash, but that this acceleration is blocked in a medium which is both sodium and calcium deficient. We also noted that calcium deficiency only elevated cGMP levels when sodium was present. For other experiments, we recorded ERG or aspartate isolated PIII responses from eyecups or retinas mounted on our quick-freeze apparatus, the light stimuli originating from the double light-bench of the latter. Whereas background illumination depressed cGMP, no detectable further cGMP loss accompanied the electrical response to a flash superimposed on the background.

(Received March 10 1992)

(Accepted June 12 1992)

Keywords

Footnotes

Reprint requests to: Adolph I. Cohen, Department of Ophthalmology and Visual Sciences Box 8096, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA.