Calcium‐tension relationships of muscle fibers from patients with periodic paralysis

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Abstract
Lateral gastrocnemius muscle biopsies from a 26‐year‐old man with hyperkalemic periodic paralysis and a 23‐year‐old man with hypokalemic periodic paralysis were studied. Both patients came from families in which older relatives had developed a vacuolar myopathy in association with their periodic paralysis. Muscle fibers were chemically skinned, and individual fibers were studied with a low‐compliance strain gauge. The tension generated by fibers was studied in baths with calcium concentrations from 10‐8 mol/L to 2.5 × 10‐5 mol/L. The Ca‐tension relationships and maximal tensions (normalized to fiber cross‐sectional area) of fast and slow twitch fibers were indistinguishable from those found in fibers from 5 normal subjects. The results reinforce earlier findings which suggested that loss of Ca‐induced myofibril contraction was not the cause of paralysis in periodic paralysis.