Biophys J, March 2001, p. 1220-1229, Vol. 80, No. 3

Voltage-Dependent Membrane Capacitance in Rat Pituitary Nerve Terminals Due to Gating Currents

Gordan Kilic^* and Manfred Lindau

 ^*University of Colorado Medical School, Department of Medicine, Denver, Colorado 80262, and  Cornell University, School of Applied and Engineering Physics, Ithaca, New York 14853 USA

We investigated the voltage dependence of membrane capacitance of pituitary nerve terminals in the whole-terminal patch-clamp configuration using a lock-in amplifier. Under conditions where secretion was abolished and voltage-gated channels were blocked or completely inactivated, changes in membrane potential still produced capacitance changes. In terminals with significant sodium currents, the membrane capacitance showed a bell-shaped dependence on membrane potential with a peak at ~40 mV as expected for sodium channel gating currents. The voltage-dependent part of the capacitance showed a strong correlation with the amplitude of voltage-gated Na⁺ currents and was markedly reduced by dibucaine, which blocks sodium channel current and gating charge movement. The frequency dependence of the voltage-dependent capacitance was consistent with sodium channel kinetics. This is the first demonstration of sodium channel gating currents in single pituitary nerve terminals. The gating currents lead to a voltage- and frequency-dependent capacitance, which can be well resolved by measurements with a lock-in amplifier. The properties of the gating currents are in excellent agreement with the properties of ionic Na⁺ currents of pituitary nerve terminals.

Biophys J, March 2001, p. 1220-1229, Vol. 80, No. 3
© 2001 by the Biophysical Society   0006-3495/01/03/1220/10  $2.00

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