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Sodium entry in rat diaphragm induced by depolarizing drugs
Author(s) -
Creese R.,
Franklin G. I.,
Mitchell L. D.
Publication year - 1977
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.1977.sp012045
Subject(s) - carbachol , decamethonium , chemistry , sodium , potassium , diaphragm (acoustics) , biophysics , medicine , endocrinology , biochemistry , receptor , biology , physics , organic chemistry , acoustics , loudspeaker
1. An increased uptake of labelled sodium was found in the end‐plate region of rat diaphragm following brief exposure to solution containing 24 Na plus carbachol (100 μ M ), with a wash in inactive saline. Tetrodotoxin (0·1 μ M ) was also present. Comparable results were obtained with decamethonium and suberyldicholine. 2. With carbachol (100 μ M ) the influx of labelled sodium at the end‐plate region was increased by a factor of at least three as compared with that at the end of the fibres. 3. After entry the labelled sodium spread along the fibres with an apparent diffusion coefficient which was half that expected in the external solution. 4. The dose—response curve for the effect of carbachol gave a half‐maximal value of 72 μ M . 5. In muscles depolarized by potassium methyl sulphate the effect of carbachol on the entry of sodium was reduced although demonstrable. 6. The entry of labelled sodium at the end‐plate was maintained during prolonged exposure to carbachol (100 μ M ) or decamethonium (100 μ M ). 7. The rate of entry of 24 Na obtained with carbachol, after corrections for the wash, was estimated as 1·5 × 10 3 ions channel −1 sec −1 , measured over a period of 15 sec. 8. Labelled decamethonium and labelled carbachol also accumulated at the end‐plate region. After extrapolation to allow for the effects of the wash the entry of decamethonium when expressed as a clearance (pl. mg −1 sec −1 ) was comparable to that of sodium, as expected if decamethonium and sodium enter through the same channels.