Nature 266, 75 - 78 (03 March 1977); doi:10.1038/266075a0

K-contractures and membrane potential in mammalian skeletal muscle

ANGELA DULHUNTY^*

New South Wales Institute of Technology, School of Life Sciences, Gore Hill, New South Wales, Australia
^*Present address: Department of Anatomy, University of Sydney, New South Wales 2006, Australia.

A FUNDAMENTAL property of skeletal muscle fibres is the ability to develop tension in response to surface membrane depolarisation. The relation between membrane potential (V _m) and tension has been measured in amphibian muscle using external potassium concentration (K₀) to clamp V _m ¹⁻⁴. A K-contracture follows exposure to high K₀ and tension is graded with K₀ between 20 mM (V _m = -50 mV) and 50 mM (V _m= -40 mV). Human intercostal muscle, however, either does not respond mechanically to K₀ of 80 mM or gives a very small contracture⁵. It is not clear whether this is a result of diffusion delays in the large bundles of fibres or whether there is a basic species difference in excitation−contraction coupling. I report here that, in bundles of fewer than 20 fibres, the relationship between K-contracture tension and K₀ is shifted to higher K₀ in rat muscle because changes in K₀ are less effective in altering V _m.

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