RELEASE OF BOUND SODIUM IN SINGLE MUSCLE FIBERS

Abstract
The activities of sodium, potassium, and hydrogen in the myoplasm of single muscle fibers from the giant barnacle were measured by cation-sensitive microelectrodes as the temperature of the bathing solution was increased from 7 to 40 °C. An irreversible shortening occurred in all fibers between 37 and 40 °C. When the fibers shortened in a sodium-free Ringer solution, the mean activity of sodium increased by 130%, the mean activity of potassium remained relatively constant, and the pH decreased from 7.17 to 6.77. The results have been interpreted as meaning that at 37–40 °C there was a disruption of the myofilaments and a release of associated sodium ions.

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