[Use of tonic contracture of strips of frog myocardium to study sodium-calcium exchange in the sarcolemma of myocardiocytes]. / Ispol'zovanie tonicheskoi kontraktury polosok miokarda liagushki dlia izucheniia natrii-kal'tsievogo obmena v sarkolemme kardiomiotsitov.

ABSTRACT

The mechanism of tonic component of the frog myocardium potassium contraction was studied. The degree of contraction depended on the potassium, sodium and calcium ions concentrations in extracellular medium. The tonic component of hyperpotassium contraction, as well as the additional contractions due to hyposodium and hypercalcium medium in the tonic component phase seems to stem from activation of sodium--calcium exchange. The latter through the sarcolemma of the heart cells was 3Na 1Ca. The effect of some mono- and bivalent cations on sodium-calcium exchange in respect ot their inhibiting activity was as follows Cd+2 greater than Sr+2 greater than Ba+2 greater than Mn+2 much greater than Mg+2 greater than Li+ greater than Cs+.