Inhibition of calcium influx and calcium current by gamma-aminobutyric acid in single synaptic terminals

Proc Natl Acad Sci U S A. 1991 Aug 15;88(16):7135-9. doi: 10.1073/pnas.88.16.7135.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Baclofen / pharmacology
  • Calcium / metabolism*
  • Calcium Channels / drug effects
  • Calcium Channels / physiology*
  • Electric Conductivity / drug effects
  • Goldfish
  • In Vitro Techniques
  • Membrane Potentials / drug effects
  • Muscimol / pharmacology
  • Neurons / drug effects
  • Neurons / physiology*
  • Picrotoxin / pharmacology
  • Retina / physiology
  • Synapses / drug effects
  • Synapses / physiology*
  • gamma-Aminobutyric Acid / pharmacology*


  • Calcium Channels
  • Picrotoxin
  • Muscimol
  • gamma-Aminobutyric Acid
  • Baclofen
  • Calcium