Prolonged action potential of glycerol-treated skeletal muscle fibres of frogs in Ca-free egta solution.

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In glycerol-treated sartorius muscle fibres, membranes were depolarized to about-30 mV when muscle fibres were perfused with Ca-free solution containing 2 mM EGTA. Under such a condition, muscle fibres were able to produce not only an initial spike potential (initial SP) but also a following slow depolarizing response (slow DR) forming a plateau phase by cathodal current pulse when membrane was previously hyperpolarized up to -80 mV by extrinsic anodal currents. The membrane conductance during a generation of these responses increased. Both initial SP and slow DR were abolished reversibly by removing external sodium ions. Tetrodotoxin (TTX) blocked a generation of the initial SP but did not affect on the slow DR. On the other hand, D-600 did not affect on the initial SP but blocked a generation of the slow DR. It is concluded that these responses are generated in the surface membrane and that the initial SP is produced by a movement of sodium ions through the sodium channels and the slow DR is produced by a movement of sodium ions through the calcium channels.
久留米大学医学部 The Kurume Medical Journal 編集部の論文