SOMAN REVERSIBLY DECREASES THE DURATION OF CA2+ AND BA2+ ACTION-POTENTIALS IN BULLFROG SYMPATHETIC NEURONS

Soman, (pinacoloxymethyl-phosphoryl fluoride) (0.1-10-mu-M) an irreversible cholinesterase inhibitor, reversibly reduced the duration of calcium (Ca2+)- and barium (Ba2+) spikes without significantly affecting spike amplitude in sympathetic postganglionic neurons of the adult bullfrog (Rana catesbeiana). The soman-induced shortening of the spike duration was not prevented by pretreatment with either (+)-tubocurarine (100-mu-M) or hexamethonium (100-mu-M) and atropine (10-mu-M) and was also recorded from acutely-dissociated sympathetic neurons. These results suggest that soman has a direct action to decrease calcium entry through voltage-dependent channels activated during a spike. This effect may contribute to both the decrease in the duration of the after-hyperpolarization (AHP) and the enhanced neuronal excitability produced by soman in these neurons.