title: Ionic membrane conductance during the time course of the cardiac action potential.
abstract: 1. Membrane ionic current-voltage (I-V) relations of the frog ventricular myocardium were measured during the action potential with a new single sucrose gap voltage clamp technique. 2. The I-V relation is linear during the plateau and rapid repolarization phases of the action potential and during the development of the regenerative threshold of repolarization. 3. Time dependent I-V relation during a series of voltage clamp pulses of clamp initiation. 4. The membrane conductance is remarkably constant during the plateau and is about 85 mumhos/muF of membrane capacitance. 5. Chloride conductance is about 18% of the total ionic conductance during the plateau and is not time dependent. Two inward Cl-movement during a normal action potential is sufficient to approximately halve the action potential duration. 6. Membrane conductance did not change significantly when Ca2+ was omitted from the bathing medium. 7. Epinephrine increased the duration of the action potential and the total ionic conductance during the platiau in normal and Ca-free media. 8. Separation of Na+ and K+ currents in muscles bathed in 'zero' Ca2+, 'zero' Cl- solution indicates that the inward and outward currents are balanced to within 2% during the slow repolarization. 9. The results indicates that a fine balance between conductance changes cardiac action potential. The possibility of a cross ionic interaction in the heart cell membrane is suggested.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001001:Anura; D001693:Biological Transport, Active; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000502:physiology; D004553:Electric Conductivity; D004837:Epinephrine / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D011188:Potassium / Q000502:physiology; D012964:Sodium / Q000502:physiology; D016276:Ventricular Function
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium; D002118:Calcium; D004837:Epinephrine