Voltage-dependent facilitation of Ca2+ entry in voltage-clamped, aequorin-injected molluscan neurons.

Abstract

Voltage-clamp experiments were performed on giant neurons of the nudibranch Anisodoris nobilis injected with the Ca-sensitive photoprotein, aequorin. Depolarization beyond -10 to +5 mV produced an aequorin signal, the amplitude of which depended on the extracellular Ca2+ concentration, the amplitude of the depolarization, and its duration. In paired pulse experiments, the amplitude of the aequorin signal produced in response to the second of 2 identical depolarizing pulses was larger than that produced during the first, resulting from an increased entry of Ca2+ during the 2nd pulse. The increment in Ca conductance inferred from the augmented signal during the 2nd pulse was independent of Ca2+ influx during the 1st pulse but was related to the amplitude and duration of the 1st pulse.