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

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 10(-14) slope conductance of 13 pS and a K+ ion permeability of P-K = 6.5 x 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 OA 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. (C) 2001 Elsevier Science B.V. All rights reserved.