Comparison between slow sodium channel inactivation in rat slow- and fast-twitch muscle.
1. Voltage-clamp Na+ currents (INa) were studied in rat soleus slow-twitch muscle fibres at about 18 degrees C using the loose-patch-clamp technique. The maximum inward current density was produced by depolarizations to about -19 mV. 2. Fast inactivation was studied utilizing 20 ms conditioning potentials. INa was reduced by 50% with conditioning potentials to about -70 mV. 3. Changes in the conditioning membrane potential produced slow changes in the peak INa due to a slow inactivation process. INa was reduced by 50% at about -86 mV due to slow inactivation. 4. The mean maximum inward INa when slow inactivation was fully removed was 6.83 mA cm-2. 5. Due to the slow inactivation process, slow-twitch fibres were less susceptible to reduction in INa than fast-twitch fibres.
D000818:Animals; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D009132:Muscles / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D007473:Ion Channels; D012964:Sodium