["Contractile" calcium and relation between the sarcoplasmic reticulum and the T-system in the myocardium and skeletal muscle].

On the basis of published experimental data a consideration of the role of Ca ions in the myocardial and skeletal muscle contractility of the warmblooded was made. It has been shown that during the relaxation period Ca concentration in the cardiomyocytes sarcoplasmic reticulum (SR) must be of the order 10(-4) M and the corresponding concentrative gradient of Ca "SR-myoplasma" of 10(3) is maximally possible at the work of Ca-pump (the greater gradients of Ca concentration are the products of individual gradients). During the contraction period Ca "SR-myoplasma" gradient is lowered at the level 1 divided by 10(1). The SR membrane Ca-pump power is approximately 10(2) times greater than one of the sarcolemmal membranes. It was shown that because of spacely morphological peculiarities of the muscle cell structure out of the whole external Ca (coupled with the sarcolemma) only the part of Ca located at T-system can take part in the contractile act. The peculiarities of the T-system structure and the interrelation of the volumes and areas of T-system and SR permit to introduce a notion about "the coefficient of using external Ca in the contractile act" (UCa) and also enable to explain the differences in cardiomyocytes and skeletal myocytes resistance to a decrease of Ca concentration in the external environment.