Characterization of outward currents in a neurosecretory cell acutely isolated from the adult rat.

Hormonal release from neurosecretory cells appears to be regulated in part by ionic currents. Because ethanol was shown to alter the release of melatonin from the cultured pineal gland, the ionic currents present in pineal cells were characterized using the whole-cell patch clamp technique. The macroscopic ionic current observed in standard solutions was dominated by an outward current component. Study of this outward component in a solution without added external Ca2+ revealed the existence of two distinct outward currents. Depolarizing command voltages from a holding potential of -100 mV activated a fast outward current which reached a peak within 20 ms and completely decayed in about 150 ms. The second outward current isolated from a holding potential of -50 mV activated at potentials positive to -20 mV. In the presence of 2 mM external Ca2+ the I-V relationship did not display a region of negative slope conductance suggesting that Ca2+-activated K+ current did not contribute significantly to the outward current. A small Ca2+ inward current was observed when these two outward components were eliminated. These results indicate that acutely dissociated pineal cells display two distinct K+ outward currents: (i) a transient current similar to the A current (IA); and (ii) a slowly activating, sustained current similar to the delayed rectifier (IK). Thus, the characterization of ionic currents in the pineal cell is of importance because they may be a target for acute and chronic ethanol actions.