Abstract
The ability of the cations Cs+ and Rb+ to substitute for K+ as agents for causing contraction has been studied in vitro in segments of human uterine muscle. The development of tension was measured isometrically. The tension produced by Cs+was identical with that produced by K+ but Rb+ was less effective than K+. This quantitative difference in response to Rb+ could not have been due to its bulk relative to the size of the membrane channels since the hydrated Crystal is intermediate between Cs+ and K+. Possible dependence on a "carrier" mechanism, specific for a single cation, could not be proved by use of inhibitors. Ouabain, though an inhibitor of the contractile response to all 3 cations, did not selectively inhibit any one cation, nor was the blocking effect of phenoxybenzamine cation-specific. Inhibition with 2,4-dinitrophenol was only evident for the response to Cs+ and K+ and this too was not specific.
Footnotes
- Accepted November 22, 1965.
- The Williams & Wilkins Comapny
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