The effects of gamma-aminobutyric acid on voltage-clamped motoneurons of the lobster cardiac ganglion.

1. We examined the electrophysiological and pharmacological effects of GABA on voltage-clamped motoneurons of the lobster cardiac ganglion. 2. GABA caused a dose-dependent current (EC50 = 0.7 mM), which reversed at the estimated Cl- equilibrium potential. 3. The conductance activated by GABA was voltage-dependent, increasing as a non-linear function of depolarization. 4. A Na(+)-dependent GABA uptake mechanism was only weakly sensitive to nipecotic acid. 5. Picrotoxin inhibited the GABA response, but bicuculline had no effect. 6. We conclude that the effect of GABA in the lobster cardiac ganglion is similar to its effect on other crustacean neuromuscular tissues and on vertebrate GABAA receptors. 7. There appear to be differences among species with respect to the physiology and pharmacology of the Na(+)-dependent GABA transporter. 8. The effect of GABA is also similar to the ionic mechanism underlying the action of histamine in the cardiac ganglion.