HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Chiarandini, D. J. Articles by Stefani, E. Search for Related Content PubMed PubMed Citation Articles by Chiarandini, D. J. Articles by Stefani, E.

1. The effects of Mn on the electrical and mechanical properties of frog muscle fibres have been studied.

2. In normal saline 10 or 20 mM-Mn hyperpolarized the fibres and had no effect on the membrane resistance. In isotonic K₂SO₄ saline, Mn increased the membrane resistance indicating that this agent reduced the conductance to K.

3. The action potential is prolonged by Mn while the overshoot amplitude is unaffected. The threshold of the action potential is shifted to more positive values of membrane potential.

4. The isometric twitch is reduced by 45% in 10 mM-Mn; this effect is observed within 8 sec of the application.

5. Mn (10 mM) reduced K contractures induced by 40 or 75 mM-K (constant [K].[Cl] product) and shifted to the right in a parallel manner the curve tension vs. log K concentration. The calculated mechanical threshold for K contractures was shifted from -48 to -33 mV.

6. Caffeine contractures (3-4 mM) and supramaximal K contractures (190 mM-K) were unaffected by 10 mM indicating that contractile proteins and the ability of the sarcoplasmic reticulum to release Ca are not impaired.

7. It is concluded that Mn is mainly affecting the excitation-contraction coupling by altering the mechanical threshold. Since Mn reduces the permeability to Ca in several excitable membranes, it is suggested that the mechanical threshold depends on the entry of Ca to the muscle.