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 °C to 22 °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 was 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.

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