Characterization of a delayed rectifier potassium channel in the slowly adapting stretch receptor neuron of crayfish

Abstract

Single channel recordings were performed on enzyme-cleaned slowly adapting sensory neurons of crayfish, in cell-attached configuration, with a physiological K + gradient across the neuronal membrane. An outward rectifying, voltage-gated K + channel with a slope conductance of 13 pS and a K + ion permeability of P K=6.5×10 −14 cm 3/s was characterized. This 13 pS K + channel started to be activated at around 20 mV depolarization. Its open probability increased upon depolarization with V 0.5=−25.3 mV and P max=0.83. The averaged currents showed a delay following the onset of depolarization. The activation time constant was voltage-dependent. The maximal value was 17.0 ms at −25 mV and at +35 mV the time constant was 1.7 ms. Little inactivation was observed throughout the 80- or 1500-ms long depolarization pulses. A sum of two exponentials provided the optimal fit for open time and closed time distribution. At 80-mV depolarization, the open time constants were 0.4 and 10.4 ms; the close time constants were 0.4 and 2.3 ms. The first-latency distribution suggested that at least two closed states preceded two open states. This 13 pS delayed rectifier plays a minor role in the maintenance of the resting membrane potential but contributes to the action potential repolarization. It may also modify the stretch-induced receptor potential and affect the adaptation behaviours in this neuron.