Membrane currents activated in acutely dissociated rat pineal cells during the circadian cycle.

Whole-cell patch-clamp recordings were performed in cells acutely dissociated from adult rat pineal glands in order to determine possible long lasting influences of the circadian rhythm upon voltage-activated membrane currents. Cells were dissociated either during the light or dark period. From a holding potential of -50 mV, pineal cells bathed in a normal solution responded to depolarizing potentials positive to -20 mV with a slowly rising sustained outward current. From a holding potential of -100 mV, a transient outward current was activated with command potentials positive to -50 mV. This current reached a peak within 15 ms and had a significant decay over 160 ms. In most of the cells, inward currents were not observed and no significant differences were found between the properties of the outward currents in cells dissociated during the light or dark period. This suggests that the previously reported circadian activity in the rat pineal gland is not associated with inward current or with long lasting changes in the voltage-activated membrane currents.