Sodium channel permeation in squid axons. II: Non-independence and current-voltage relations.
1. The concentration and voltage dependence of current through the Na channels of squid giant axons was studied. The permeant cations Na, K and ammonium were used. 2. The Na channel current at a fixed voltage saturates as the internal permeant ion concentration is increased. The half-saturation activities at 50 mV were found to be 623, 268, 161 mM for Na, NH4, and K, respectively. These Km values for Na and K appear to be voltage-dependent. 3. Instantaneous current-voltage relations were determined with two different internal Na concentrations and with Na outside and K inside. 4. A three-barrier, two-site ion permeation model previously used in describing Na channel reversal potentials is shown here to account for the Na channel currents as well.
D000818:Animals; D001369:Axons / Q000502:physiology*; D049832:Decapodiformes; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008959:Models, Neurological; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D011188:Potassium