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Sodium and calcium components of action potentials in Aplysia giant neurone
Author(s) -
Geduldig D.,
Junge D.
Publication year - 1968
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1968.sp008657
Subject(s) - calcium , aplysia , sodium , chemistry , biophysics , tetrodotoxin , neuroscience , biology , organic chemistry
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.