Article date: 1991/8/15
PubMed ID: 2427978
Journal name: Proceedings of the National Academy of Sciences of the United States of America (ISSN: 0027-8424)
Inhibition of Ca influx and Ca current by gamma-aminobutyric acid (GABA) was studied in single synaptic terminals of isolated retinal bipolar neurons. Measurements of intracellular Ca concentration [( Ca]i) using the fluorescent Ca indicator fura-2 showed that GABA potently inhibited Ca influx into the terminal elicited by high extracellular K concentration ([K]o). This inhibition was attributed to GABA type A (GABAA) receptor-activated chloride ion conductance that prevented bipolar neurons from depolarizing sufficiently to activate the Ca current, even in response to increased [K]o. Patch-clamp recordings of the Ca current revealed a second effect of GABA: GTP-dependent inhibition of the Ca current. This inhibition was not mediated by GABAA receptors, but baclofen, which binds to the GABA type B (GABAB) receptor and is known to inhibit the Ca current in other systems, was not able to mimic the action of GABA. This suggests the involvement of a different type of GABAB-like receptor in the inhibition of Ca current by GABA. GABA did not cause an overall suppression of the Ca current; rather, the voltage-dependence of Ca-channel activation was shifted to more depolarized potentials. Thus, maximal inhibition of the Ca current by GABA occurred in the physiological range of potential.
Author List: Heidelberger R, Matthews G
Publication Types: Journal Article; Research Support, U.S. Gov't, P.H.S.
Substances mentioned in the article: Calcium Channels; Picrotoxin; Muscimol; gamma-Aminobutyric Acid; Baclofen; Calcium;
Mesh terms: Animals; Baclofen/pharmacology; Calcium/metabolism; Calcium Channels/drug effects; Electric Conductivity/drug effects; Goldfish; In Vitro Techniques; Membrane Potentials/drug effects; Muscimol/pharmacology; Neurons/drug effects; Picrotoxin/pharmacology; Retina/physiology; Synapses/drug effects; gamma-Aminobutyric Acid/pharmacology;
Citations: - 2557620