Potentiation of a transient outward current by Na+ influx in crayfish neurones.
In voltage-clamped "motor-giant" neurones of the crayfish Orconectes limosus a depolarizing voltage step elicits a transient inward current carried by Na+ which is followed by an early and a delayed outward current. The early outward current is reduced if the Na+ current is suppressed by tetrodotoxin or the removal of external Na+. It is also abolished if the K+ channel blocking agents tetraethylammonium and 3,4-diaminopyridine are applied to the neurone. The outward current was not depressed if Li+ was substituted for Na+ in the external solution or if the Na-K pump was inhibited by ouabain or the removal of external K+. Ionophoretic injections of EGTA did not depress the early outward current. Short ionophoretic injections of Na+ into the neurone increased the outward current elicited by a depolarization but did not affect the leakage current. It is suggested that the influx of Na+ leads to a transient increment of the Na+ concentration near K+ channels and that internal Na+ ions exert an activating or modulating effect on K+ channels.
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D015761:4-Aminopyridine / Q000031:analogs & derivatives*; D000077770:Amifampridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D003400:Astacoidea; D004533:Egtazic Acid / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D009046:Motor Neurons / Q000378:metabolism* / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D000631:Aminopyridines; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D004533:Egtazic Acid; D010042:Ouabain; D019789:Tetraethylammonium; D012964:Sodium; D015761:4-Aminopyridine; D000077770:Amifampridine