Soman reversibly decreases the duration of Ca and Ba action potentials in bullfrog sympathetic neurons

Soman, (pinacoloxymethyl-phosphoryl fluoride) (0.1–10 μM) 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 μM) or hexamethonium (100 μM) and atropine (10 μM) 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 spike after-hyperpolarization (AHP) and the enhanced neuronal excitability produced by soman in these neurons.