Electrolytes and Arterial Muscle Contractility

THAT changes in ionic gradients affect contractility and excitability has been shown in skeletal muscle,' cardiac muscle' ° and nerve." The reduction of external sodium causes reduction and eventual loss of excitability in nerve and skeletal muscle, supposedly because depolarization is due to the entry of sodium into the cell. The precise effect of alterations in external sodium on contractility of muscle is not known. Contraction of skeletal muscle and cardiac muscle is associated with potassium loss. Increasing the external potassium or decreasing internal potassium tends to cause contracture and a decrease in excitability in cardiac and skeletal muscle."