Control of calcium current in rat sympathetic neurons by norepinephrine.

Inward voltage-dependent calcium currents were recorded from clamped rat sympathetic ganglion cells using either one or two microelectrodes. Suppression of potassium current was achieved by applying tetraethylammonium (TEA) externally and TEA plus cesium internally. Peak ICa was observed at 0 mV. ICa was abolished by perfusing cadmium or low calcium medium. ICa was reduced by adding norepinephrine (1-50 micrometers). This effect was not accompanied by any major change in the voltage sensitivity or time course of the residual calcium current. It is suggested that norepinephrine acts by reducing the number of available calcium channels.