Measurement of electrogenic-pump current in Aplysia neurones with constant-current and constant-voltage techniques.

1. The responses of the abdominal and pleural giant cells to warming and cooling were studied using constant-current and constant-voltage techniques. 2. The potential change upon warming from about 7 degrees C to 22 degrees C was reversed by application of maintained inward current. The reversal potential was -77 +/- 12 mV. 3. The membrane conductance increased with warming, but was not affected by pump-blocking agents. 4. The electrogenic-pump current was found to be about 16 nA for a model in which the pump acted across the membrane ionic conductance. This model could explain the reversal of the warming response with hyperpolarization. 5. In voltage-clamped cells, the response to warming was converted from an outward to an inward current by hyperpolarization. The reversal potential for the current response 31 +/- 7 mV more negative than resting, or about --80 mV. 6. The pump currents measured under voltage-clamp conditions were the same as those calculated for the hyperpolarizing responses in unclamped cells.