Ca2+ dependence of dark- and light-adapted flash responses in rod photoreceptors.
Light adaptation is thought to be orchestrated by a Ca2+ feedback signal that desensitizes the response by speeding recovery. To evaluate the role of Ca2+ in adaptation, we compared the effect of lowered Ca2+ on response properties in darkness and during adaptation. Internal Ca2+ was reduced from its normal resting dark level (535 nM) by either background illumination or exposure to Ringer's solution containing low Ca2+ and/or cyclic GMP-gated channel blockers in darkness. Ca2+ reductions in light decreased the activation gain of the transduction process and speeded recovery kinetics, while equivalent Ca2+ reductions in darkness caused similar gain reduction without accelerating recovery. This indicates that adaptational changes in the response are not due purely to feedback effects on recovery.
Gray-Keller
M P
MP
Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195, USA.
Detwiler
P B
PB
D000221:Adaptation, Ocular / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D003623:Dark Adaptation / Q000187:drug effects* / Q000502:physiology; D004594:Electrophysiology; D008116:Lizards; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012680:Sensitivity and Specificity
D002118:Calcium