EFFECTS OF ION-TRANSPORT INHIBITORS ON D2O INDUCED ACTION-POTENTIAL IN CHARACEAE

Substitution of the solvent H2O, with D2O, induced excitation in the C hara cell. The phenomenon, 'D2O-induced action potential' (DAP), was c haracterised by abrupt membrane depolarisation with incomplete repolar isation, Electrophysiological studies on the subcellular level (perfus ed plasmalemma and reconstituted channels in BLM) revealed a mechanism of channel activation similar to the electrically evoked action poten tial. In the present study the origin of DAP was analysed pharmacologi cally on intact internodal cells and thus the previous findings obtain ed on subcellular systems could be checked. The first pre-depolarisati on DAP phase was significantly prolonged by depletion of external Ca2 with EGTA. The DAP spike was diminished with Cl- channel inhibitors, 9-anthracene-carboxilic acid and ethacrynic acid. The repolarisation p hase was prolonged with tetraethylammonium chloride and Cs+ (K+ channe l inhibitors) or could be abolished by less specific cation transport inhibitors, La3+ and diethylstilbestrol. Thus, it was suggested, that the Cl- current was the main ion flux underlying the DAP spike, and th at it was activated by a Ca2+ inward current (i.e. rise in [Ca2+](i)), which was the first membrane response to D2O. In fact, D2O-induced ri se in [Ca2+](i) was observed by fura-2 fluorescence measurements. The K+ channels could give the main contribution to the repolarisation pha se, but they were apparently partially blocked by D2O. (C) 1997 Elsevi er Science Ireland Ltd.