Delayed rectifier potassium current in dissociated bullfrog primary afferent neurons.

Cultured bullfrog dorsal root ganglion cells were voltage-clamped in the whole-cell configuration. The classical delayed rectifier potassium current (IK) was separated from other ionic currents. Tetraethylammonium (1-50 mM) depressed the amplitude of IK in a concentration-dependent manner, a complete block occurring with 30 mM. With the concentration of potassium ions in the superfusate at 20 mM, the reversal potential of IK amounted to about -30mV. IK was activated between -30 and +70 mV. The half activation of IK occurred at +15 mV. The amplitude of IK was increased e-fold with 13.6 mV depolarization. The time constant of IK de-activation was shortened with membrane hyperpolarization (tau congruent to 4 ms at -100 mV). Finally, reciprocal time constant (tau -1) of the de-activating IK was increased e-fold with congruent to 13 mV hyperpolarization. It appears that the properties of IK in amphibian afferent neurons are comparable to those which have been observed with respect to the IK of the squid giant axons (Hodgkin and Huxley, 1952).