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pubmed:abstractText |
1. Action potentials resulting from direct stimulation can be recorded from the soma of the Aplysia giant neurone (located in the visceral ganglion) in sodium-free and in calcium-free external solutions. The neurones were impaled by internal micro-electrodes throughout the change of external solutions.2. Complete replacement of either sodium or calcium in the bathing medium with Tris results in only a partial reduction of spike overshoot. Simultaneous replacement of both sodium and calcium reversibly and quickly abolishes the spike.3. The sodium component of the spike in a calcium-free medium is blocked by tetrodotoxin; the drug has no effect on the calcium-dependent spike in sodium-free medium. Externally applied cobalt chloride blocks only the calcium-dependent component.4. In calcium-free media, the overshoot value varies with sodium concentration in the manner predicted for a sodium electrode. In sodium-free media, the membrane behaves like a calcium electrode.5. These results suggest that, during the normal action potential, both sodium and calcium act as carriers of the inward-directed current.
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