Modulation of inward rectifier potassium channel by toosendanin, a presynaptic blocker

The effect of toosendanin, a presynaptic blocker. on the inward rectifier p otassium channel (K-Kir) of hippocampal CA1 pyramidal neurons of rats was s tudied by the single-channel patch-clamp technique. The results, showed tha t toosendanin had an inhibitory effect on k(Kir) in an excised inside-our p atch of the neuron under a symmetrical 150 mM KC condition. By decreasing t he slower open time constant and increasing the slower close time constant, toosendanin (1 x 10 (6)- 1 x 10 (-4) g/ml) significantly reduced the open probability of the channel in a concentration-dependent manner. Meanwhile. a dose-dependent reduction in unitary conductance of the channel was also d etected after toosendanin application. These data offer an explanation for toosendanin-induced facilitation of neurotransmitter release and antibotuli smic effect of the drag. (C) 2001 Elsevier Science Ireland Ltd and the japa n Neuroscience Society. All rights reserved.