Contractile repriming in snake twitch muscle fibres.

1. Contractile repriming has been studied in voltage-clamped snake twitch muscle fibres. Maintained depolarization causes a contractile response which inactivates after a few seconds. Repolarization of the fibre can restore its ability to contract to a subsequent depolarization. This restoration, or repriming, depends on the magnitude and the duration of the repolarization. At -100 mV the minimal period of repolarization which restores contractile response is 0.38 sec. The time for recovery to half maximal tension is about 0.68 sec, and restoration is complete at about 4 sec.2. Repolarization to smaller levels of membrane potential results in a slower rate of repriming. For example, at -60 mV the mean minimal time for repriming was 2.89 sec, and nearly 17 sec of repolarization was required for full restoration of contractile response.3. The rate of repriming was not influenced by lowering the external sodium concentration.4. Repriming could be produced by repetitive, brief pulses of repolarization.5. The restoration of contractile response and of outward inactivating current showed similar time courses.