Zinc ions block rectifier potassium channels and calcium activated potassium channels at the frog motor nerve endings.
The effect of Zn2+ on presynaptic currents was investigated on frog cutaneous pectoris nerve-muscle preparations. Nerve terminal spikes were recorded with extracellular electrodes placed in the perineurial sheaths of motor nerves. Zinc ions reversibly suppressed the component of the waveform associated with K+ currents--unmasking an inward current at the terminal--and induced repetitive firing when were applied to preparations perfused with calcium containing solutions. In experiments in which delayed rectifier channels were blocked by 3,4-diaminopyridine, Zn2+ caused a prolonged and reversible inward current associated with a slight decrease in the peak calcium current generated by 3,4-diaminopyridine. Zinc ions abolished the plateau calcium current produced by the simultaneous action of 3,4-diaminopyridine and tetraethylammonium. Finally, in all the preparations in which the exposure to Zn2+ was prolonged it was observed a dramatic and irreversible reduction of the presynaptic currents. These results suggest that Zn2+ has, at least, four different effects on presynaptic currents: (1) blockade of delayed rectifier potassium currents, (2) blockade of calcium-activated potassium currents, (3) blockade of calcium currents and (4) a delayed and irreversible disruption of all ionic conductances of the terminal.
Servei de Neurologia, Facultat de Medicina, Hospital Princeps d'Espanya, Universitat de Barcelona, Spain.
F
F
Miralles
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Canti
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J
Marsal
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J
Peres
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Solsona
D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000077770:Amifampridine; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004492:Edetic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000294:innervation; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011894:Rana pipiens; D012867:Skin / Q000294:innervation; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology*
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D004492:Edetic Acid; D015761:4-Aminopyridine; D015032:Zinc; D000077770:Amifampridine; D002118:Calcium