Sodium and calcium currents of acutely isolated adult rat superior cervical ganglion neurons

Abstract

Neurons enzymatically isolated from the adult rat superior cervical ganglion (SCG) were investigated using the whole-cell variant of the patch-clamp technique. Current-clamp studies revealed the following mean passive and active membrane properties: resting membrane potential, -54.9 mV; input resistance, 349 M omega; action potential (AP) threshold, -29.8 mV; AP overshoot, 53.3 mV; AP maximum rate of rise, 166.4 V/s; and AP duration, 3.2 ms. Chemosensitivity to acetylcholine remained intact following enzymatic dispersion. Voltage-clamp studies of a transient tetrodotoxin-sensitive Na+ current revealed activation and inactivation processes which could be fit to modified Boltzmann equations. Na+ current activation parameters for the half activation potential (Vh) and slope factor (K) were -23.3 mV and 5.3 mV, respectively. Inactivation parameters for Vh and K were -59.3 mV and 7.6 mV, respectively. Voltage-clamp studies also revealed a high voltage-activated sustained inward current which was eliminated upon removal of external Ca2+, greatly reduced by 500 microM Cd2+, and supported by Ba2+ or Sr2+. Tail current analysis of this Ca2+ current revealed a sigmoidal activation. A low voltage-activated transient Ca2+ current was not observed. We conclude that isolated SCG neurons retain the properties of neurons in intact ganglia and provide several advantages over conventional preparations for the study of voltage-gated membrane currents.