Voltage-dependent membrane capacitance in rat pituitary nerve terminals due to gating currents.
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 approximately -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.
University of Colorado Medical School, Department of Medicine, Denver, Colorado 80262, USA.
G
G
Kilic
M
M
Lindau
D000818:Animals; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D009411:Nerve Endings / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010904:Pituitary Gland, Posterior / Q000294:innervation*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000502:physiology
D015222:Sodium Channels