Potassium currents of acutely isolated adult rat superior cervical ganglion neurons.

K+ currents of adult rat superior cervical ganglion neurons were studied using the voltage-clamp technique. Neuronal somata were dissociated from the ganglion using an enzymatic dispersion technique and voltage-clamped using the whole-cell patch-clamp technique. In solutions designed to isolate K+ currents, depolarization from a prepulse potential of -100 mV induced both transient and sustained outward current components. The transient current was completely eliminated by depolarization to -50 mV. The remaining sustained current component could be separated further into Ca2+-sensitive and Ca2+-insensitive components by superfusion with a Ca2+-free external solution. The transient current, which could be isolated by digital subtraction, rose rapidly and decayed over the subsequent 80 ms. Reversal potential determinations in different K+-containing solutions demonstrated that the current was carried primarily by K+. The transient current showed voltage-dependent inactivation, showing 50% inactivation near -87 mV and was completely inactivated at potentials more positive than -60 mV. The transient current recovered from inactivation with a voltage-dependent time course, the time course of inactivation decreasing with hyperpolarization. This transient outward current had characteristics of IA. The sustained Ca2+-insensitive outward current showed little decay over 800 ms and was also carried primarily by K+. This current component had characteristics similar to the delayed rectifier. A third sustained outward current eliminated by superfusion with Ca2+-free external solution had characteristics similar to the Ca2+-dependent K+ current.