A comparative study of charge movement in rat and frog skeletal muscle fibres.

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Abstract
The middle of the fiber voltage-clamp technique (Adrian and Marshall), modified where necessary for electrically short muscle fibers, was used to measure non-linear charge movements in mammalian fast twitch (rat extensor digitorum longus), mammalian slow twitch (rat soleus) and frog (sartorius) muscles. The maximum amount of charge moved in mammalian fast twitch muscle at 2.degree. C in hypertonic solution, was 3-5 times greater than in slow twitch muscle. The voltage distribution of fast twitch charge was 10-15 mV more positive when compared to slow twitch. In both mammalian muscle types hypertonic Ringer solution negatively shifted the voltage distribution of charge some 6 mV. The steepness of charge moved around mechanical threshold was unaffected by hypertonicity. The amount of charge in frog sartorius fibers at 2.degree. C in hypertonic solution was .apprx. 1/2 of that in rat fast twitch muscle; the voltage distribution of the frog charge was similar to rat soleus muscle. Warming between 2 and 15.degree. C had no effect on either the amount or steady-state distribution of charge in mammalian or frog muscles. At 2.degree. C the kinetics of charge movement in fast and slow twitch mammalian muscles were similar and 2-3 times faster than frog muscle at the same temperature. In fast and slow mammalian fibers at 2.degree. C similar times were taken to shift the same fractions of the total amount of charge. The Q10 of charge movement kinetics was between 1.2 and 2.0 in the 3 muscles studied.