The effect of dopamine on the voltage-dependent ionic channels of enzymatically dispersed glomus cells from rabbit carotid bodies was studied. Whole-cell currents were recorded on isolation with patch electrodes and dopamine applied to the bath solution. Dopamine at nanomolar concentrations produced a reversible attenuation of the calcium current whereas sodium and potassium currents remained unaltered. Dopamine inhibition of Ca2+ current was observed in all cells tested (n= 48) and at a saturating concentration (1μM) the average reduction was of 40 ± 6.5% (n= 8). The effect of dopamine was probably caused by a decrease in the number of channels activatable on depolarization since it did not modify the voltage-dependent parameters of the current. These results indicate that dopamine, which is the major transmitter secreted by glomus cells, regulates further transmitter release by feedback inhibition of Ca2+ channels.