The effect of procaine on snake twitch muscle fibres.

1. The effect of procaine on the contractile responses of voltage clamped snake twitch muscle fibres has been investigated. Procaine hydrochloride shortened the duration of contractures produced by long depolarizing pulses. It also reduced the amount of inactivating outward current.2. The rate of repriming was greatly slowed by procaine. At -80 mV, for example, the time to half restoration of contractile response was 6 sec in procaine (5 x 10(-3), w/v) as compared to 1.15 sec in tetrodotoxin (TTX), (1 x 10(-7) w/v). At -100 mV, repriming was still much slower in procaine. However, at -150 mV, repriming in procaine was quite rapid, the time to half recovery being about 0.4 sec.3. After prolonged exposure to procaine, subthreshold depolarizing pulses produced a marked diminution in the contractile response to a subsequent supermaximal depolarization. In some fibres complete inactivation could be produced in the presence of procaine without any contractile response having occurred.