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. Currentclamp studies revealed the following mean passive and active membrane properties: resting membrane potential, −54.9 mV; input resistance, 349 MΩ; 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 forVh andK were −59.3 mV and 7.6 mV, respectively. Voltage-clamp studies also revealed a high voltageactivated sustained inward current which was eliminated upon removal of external Ca²⁺, greatly reduced by 500 μM 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 voltagegated membrane currents.