M-type potassium current in dissociated sympathetic ganglion cells of Xenopus laevis

Whole-cell/voltage-clamp recordings were made from dissociated sympathetic neurons of Xenopus laevis. Step depolarization (10-70 mV, 0.5 s) from the holding potential of -65 mV activated a non-inactivating potassium current which was selectively blocked by barium (1 mM). The current did not require an inward calcium current for its activation. The steady-state activation curve of the current was centered at -35 mV with a slope factor of 8.6 mV. The time constant for activation of the current was about 115 ms when measured at -35 mV and the effective valence of the voltage-sensing particle was 2.9. This potassium current was identified as a particular set of potassium currents usually referred to as M-current.