Sodium p-chloromercuribenzoate induced delayed after depolarizations of guinea pig papillary muscles

Sulfhydryl inhibitor sodium p-chloromercuribenzoate (PCMB) 60 vmol/L caused the reduction of resting potential (RP), action potential amplitude (APA). action potential duration (APD) and the maximal rate in rising the action potential (Vmax) of guinea pig papillary muscles. Finally the delayed afterdepolarization (DAD) occurred. The occurrence of DAD in 20 experiments were 20% after 5 min, 40% after 10 min. 80% after 20 min, 95% after 30 min treated with PCMB, respectively. The resting potential was - 75+9 mV (n=19) when the DAD occurred. The amplitude of DAD depended on the basic cycle length (BCL), ie the amplitude of DAD enhanced by shortening the BCL. When it was large enough to bring the membrane potential to the threshold. a triggered impulse arose. Elevation of KCl from 3 to 6 mmol/L or addition of TINO3 2 mmol/L suppressed or abolished the DAD. Since the sodium pump activator (TI+. K+) counteracts PCMB-induced DAD, it is supposed that this DAD may be induced by severe sodium pump inbibition.