Effects of GABA on horizontal cells in the tiger salamander retina.
Application of gamma-aminobutyric acid (GABA) slows down the horizontal cell response time course (HCRRT) and induces membrane depolarization in horizontal cells (HCs) after synaptic inputs are blocked by Co2+. We present evidence that suggests both effects are probably mediated by GABAA receptors which open chloride channels in the HC membrane. In any given concentration of GABA, ranged from 0 to 100 microM, the HC membrane potential (VHC) in saturating light and in the presence of 100 microM Co2+ are identical. This result suggests that GABA in both light and 100 microM Co2+ opens the same amount of chloride channels (same gCl) so that VHC determined by chloride and leak conductances has the same value. Higher concentrations of Co2+ (> 300 microM) not only blocks synaptic transmission from photoreceptors to HCs, but also acts as an antagonist that suppresses the GABA-mediated depolarization in HCs.
Yang
X L
XL
Cullen Eye Institute, Baylor College of Medicine, Houston, TX 77030.
Wu
S M
SM
D000557:Ambystoma; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects; D010775:Photic Stimulation; D012160:Retina / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D013569:Synapses / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002413:Cations, Divalent; D003035:Cobalt; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline