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Journal of Experimental Biology 32,383-396 (1955)
Published by Company of Biologists 1955

Ionic Regulation in the Muscle Fibres of Carcinus Maenas : I. The Electrolyte Composition of Single Fibres

J. SHAW ¹

¹ Department of Zoology, University of Durham, King's College, Newcastle upon Tyne

1. Measurements have been made of the concentrations of potassium, chloride, calcium and magnesium, the conductivity and the membrane potential of single isolated fibres of the carpopodite extensor and flexor muscles of Carcinus maenas.

2. Analyses of whole muscles gave the total concentration of the cations as 224 mM./kg. H₂O, of which potassium accounted for 120 mM./kg. and sodium 54 mM./kg. Of the anion fraction chloride only accounted for 54mM./kg. H₂O. The analyses of the separated fibres were the same as for the whole muscle.

3. The average specific resistance of the fibres is 56-cm. This represents a concentration of muscle ions of about 200 m.equiv./kg. and the electrolyte content of the muscle is not much more than a third of that of the blood. Between 72 and 91% of the total muscle fibre cations are present in an ionized form.

4. The average membrane potential is 58 mV. The ratios of the concentrations of potassium ions and chloride ions in the blood and muscle fibres suggest that these ions may be passively distributed across the membrane. The low concentration of sodium ions in the fibre probably indicates the operation of a ‘sodium pump’ as has been proposed for vertebrate muscles. The distribution of calcium and magnesium cannot be explained in simple terms.

5. The correspondence between the equilibrium potentials for potassium and chloride ions and the membrane potential suggests that theory of ion distribution put forward by Boyle & Conway for frog's sartorius muscle may also be applicable to Carcinus muscles.