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

The kinetics of the TEA and 4-AP sensitive K+ current (IK) in the slowly adapting lobster stretch receptor neurone were investigated in sub- and near-threshold voltage regions using electrophysiological and pharmacological techniques. In dynamic conditions IK was found to display both 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 K inactivation could be shown to be unrelated to K+ flux dependent changes in intra- and pericellular K+ concentrations. Its stationary voltage dependence was however shifted in a depolarizing direction by increasing, and in hyperpolarizing direction by decreasing the extracellular Ca++ concentration. In view of these findings, and of 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 could however be obtained in a voltage range from about -100 to about -40 mV. The experimental observations were utilized in the formulation of a mathematical model describing the kinetic behaviour of IK in the present preparation based on constant field and state transition theories.