Mechanisms underlying the M-current block by barium in bullfrog sympathetic neurons

Whole-cell/voltage-clamp recordings were made from dissociated bullfrog sym pathetic neurons to examine the channel blocking actions of barium (3-2000 mu M) on an M-type potassium current (I-M). Barium (IC50 approximate to 105 mu M) blocked I-M without affecting the 50%-activation voltage (approximat e to -35 mV) and the slope factor (approximate to 11 mV) of the activation cu Ne. The results indicate that the barium block is independent of the kin etics of I-M. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.