Cable parameters, sodium, potassium, chloride, and water content, and potassium efflux in isolated external intercostal muscle of normal volunteers and patients with myotonia congenita
myotonia congenita vs. normal): the membrane resistance was greater (5729 vs. 2619 ω·cm2), the internal resistivity was less (75.0 vs. 123.2 ω·cm), the water content was less (788.2 vs. 808.2 ml/kg wet weight), and the mean resting potential was greater (68 vs. 61 mv). No significant differences were found with respect to the following variables: K+ content (73.5 vs. 66.7 mEq/kg wet weight) and the calculated intracellular K+ concentration (215 vs. 191 mEq/liter fiber water), fiber capacitance (5.90 vs. 5.15 μf/cm2), Na+ content (97.7 vs. 94.1 mEq/kg wet weight), Cl- content (79.0 vs. 74.7 mEq/kg wet weight), mannitol extracellular volume (45.1 vs. 46.6 cc/100 g wet weight), and K+ efflux (23.2 vs. 21.5 moles × 10-12 cm-2·sec-1). These abnormalities of skeletal muscle in human myotonia congenita are like those of skeletal muscle in goats with hereditary myotonia. We tentatively conclude that a decreased Cl- permeability accounts for some of the abnormal electrical properties of skeletal muscle in myotonia congenita.
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