MULTIPLE PICROTOXININ EFFECT ON GLYCINE CHANNELS IN RAT HIPPOCAMPAL-NEURONS

The effect of picrotoxinin on glycine-induced chloride currents was st udied in dissociated rat hippocampal neuron culture in whole-cell and excised outside-out patches. Picrotoxinin blocked the glycine induced chloride currents. The picrotoxinin effect at 20 mu M on glycine dose response relationship suggested a competitive mechanism. However, at 1 mM, the picrotoxinin effect was largely noncompetitive. In excised pa tches, glycine activated two types of channels distinguished by a diff erence in conductances. The first group had single channel conductance s of around 47 pS and another around 100 pS. Occasionally, both types of channels were found in the same excised patch. Low concentration of picrotoxinin selectively blocked large conductance channels. At highe r concentrations of 0.5 to 1 mM, picrotoxinin blocked the small conduc tance channels by a flickering block. These findings indicate that the whole-cell glycine current in rat hippocampal neurons is mediated by at least two types of channels. The two types of channels have distinc t conductance, picrotoxinin sensitivity and different mechanism of pic rotoxinin block. (C) 1998 IBRO. Published by Elsevier Science Ltd.