Extracellular calcium ions entering via slow voltage-sensitive channels are required for excitation-contraction coupling during depolarization contractures but not during electrically evoked twitches in rat skeletal muscle.
Should not alter clinical calcium-channel blocker use; extends mechanistic understanding of calcium entry in rodent skeletal muscle.
The effects of the organic calcium channel blocker nitrendipine was tested on electrically evoked twitches and on potassium depolarization-induced contractures of rat lumbricalis muscles. Nitrendipine (10(-7) to 5 X 10(-5) M) blocked only the potassium contractures. It was concluded that blocking calcium uptake through the slow voltage-sensitive calcium channels during potassium depolarization blocks the mechanical response of the muscle. Thus extracellular calcium ions are required for the excitation-contraction (E-C) coupling during depolarization contractures. On the other hand, electrically evoked twitches were not affected by nitrendipine; therefore, extracellular calcium ions entering via the slow voltage-sensitive channels are not required for E-C coupling during the twitch.
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Frank et al. (1988) studied this question.
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