title: Prolonged action potential of frog skeletal muscle membrane in Ca-free EGTA solution.
abstract: The membrane of isolated frog skeletal muscle fibers with or without T-system is depolarized to about -30 mV in a Ca-free solution containing 2 mM EGTA. Under such a condition, the action potential can be produced by a cathodal pulse when the membrane is previously hyperpolarized to -70- -100 mV by a conditioning anodal current. The action potential consists of two different potential components, namely a spike potential and a following slow depolarizing response forming a plateau phase (plateau potential). The membrane conductance during the plateau potential is increased. Both spike and plateau potentials are abolished in the absence of NaCl. TTX blocks a spike potential without affecting a plateau potential, whereas Mn and D-600 act contrarily. The i-v relation shows an anomalous rectification in Na-free solution, suggesting that the K conductance during the plateau phase is decreased. It is suggested that spike and plateau potentials are produced by a movement of sodium ions through sodium and calcium channels of the membrane, respectively.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011898:Ranidae; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D005711:Gallopamil; D013779:Tetrodotoxin; D004533:Egtazic Acid; D012964:Sodium; D002118:Calcium