Kinetics of the TEA and 4-AP sensitive K+ current in the slowly adapting lobster stretch receptor neurone

Abstract

The kinetics of the TEA [tetraethylammonium chloride] and 4-AP [4-aminopyridine] sensitive K+ current (IK) in the slowly adapting lobster stretch receptor neuron were investigated in sub- and near-threshold voltage regions using electrophysiological and pharmacological techniques. In dynamic conditions, IK displayed fast and slow reactions. These were attributed to a Hodgkin-Huxley type of K activation and a slow type of K inactivation, respectively. The slow inactivation was unrelated to K+ flux dependent changes in intra- and pericellular K+ concentrations. Its stationary voltage dependence was shifted in a depolarizing direction by increasing and in a hyperpolarizing direction by decreasing the extracellular Ca2+ concentration. Based on these findings and its kinetic properties, the slow K inactivation was classified as a genuine channel gating process. The process of K activation was too fast for a dynamic analysis with the recording technique available. An estimate of its stationary voltage dependence was obtained in a voltage range from .apprx. -100 to .apprx. -40 mV. These observations were used in the formulation of a mathematical model describing the kinetic behavior of IK in the present preparation based on constant field and state transition theories.