HG2-ACTIVATED CL- CHANNELS IN APLYSIA NEURONS( INCREASES THE OPEN PROBABILITY OF CARBACHOL)

CARBACHOL and acetylcholine (ACh)-activated whole-cell chloride curren ts were recorded in identified neurons of Aplysia californica. Applica tion of 0.1-10 mu M HgCl2 potentiated the chloride response and reduce d the rate of desensitization. To investigate the underlying mechanism we recorded single chloride channels in a cell-attached patch configu ration. Recordings were performed successively on the same neuron with 1 mu M carbachol and with 1 mu M carbachol + 1 mu M HgCl2, respective ly. The slope conductance did not change significantly, but there was a manyfold increase in the open probability, p(o). This may underlie t he Hg2+ -induced enhancement of carbachol- and ACh-evoked chloride cur rents in Aplysia neurons and may serve as a model for the neurotoxic e ffect of Hg2+ on the mammalian ACh receptor.