Science · 1969 · 22 citations · 9 references
Natural SciencesBiophysicsPhysiologyElectrophysiologyIon Channel BiophysicsMembrane BiophysicsCardiac PhysiologyIon Channel PhysiologyIon ChannelsMembrane ElectrophysiologyMembrane PotentialSodium Channel BiophysicsDepolarizationIon Equilibrium PotentialSodium Channel InactivationSodium Channel PhysiologySodium Equilibrium PotentialVoltage-clamp AnalysisVoltage-clamp RecordingVoltage-clamp Techniques
Membrane currents were measured in thin bundles of dog ventricular myocardium under voltage-clamp conditions. A rather large initial inward current which had an equilibrium potential at about + 55 millivolts could be recorded. When the external sodium concentration was reduced, the equilibrium potential for this current was shifted by the amount predicted theoretically for a current carried solely by sodium ions. The size of the sodium inward current (I(Na)) was largely dependent on the preceding membrane potential. The I(Na) was completely inactivated if the membrane potential was as low as -45 millivolts. Sodium ions are the main carrier of charge during the rapid depolarization phase of the action potential.
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