Effect of Calcium on Slow Force Responses in Isolated Right Ventricle Preparations of Healthy and Hypertrophied Myocardium in Male and Female Rats.

Effect of different Ca2+ concentrations in the bathing solution [Ca2+]o on the parameters of single isometric contraction and slow force response to stretching was studied in isolated preparations of healthy and hypertrophied myocardium of male and female Wistar rats. In all groups of experimental animals, the increase in calcium concentration was followed by a decrease in the myocardium slow response intensity. We revealed a complementary relationship between the current and medium-term systems of myocardial contractility regulation by the length of the myocardium aimed at the maintenance of the constant level during adaptation to the load. Slow responses of the hypertrophied rat heart myocardium were suppressed in comparison with those in the healthy myocardium and their intensity did not depend on animal sex.

Contractility of Right Ventricular Myocardium in Male and Female Rats during Physiological and Pathological Hypertrophy.

Sex differences in the morphogenesis and adaptation of the mechanisms controlling myocardium contractility during physiological and pathological hypertrophy of the right ventricle were demonstrated in mature rats. The study revealed sex-dependent effects of physiological and pathological cardiac hypertrophy on the coefficient of variation of the cardiomyocyte diameter, length-dependent control of the contractile force, and the maximum velocity of isotonic shortening.

[MORPHOLOGICAL AND VISCOELASTIC PROPERTIES OF ISIAH RATS MYOCARDIUM DURING THE DEVELOPMENT OF ARTERIAL HYPERTENSION].

The comprehensive study of morphometrical parameters and viscoelastic properties of right ventricle and left ventricle papillary muscles of ISIAH rats during the development of arterial hypertension has been carried out. It is established the significant increase of the index of heart mass to body mass and to tibia length of ISIAH rats in comparison with WAG rats of the same age. There are no any significant differences of "stress-strain" dependences of all experimental groups.

Activation sequence as a key factor in spatio-temporal optimization of myocardial function.

Using one-dimensional models of myocardial tissue, implemented as chains of virtual ventricular muscle segments that are kinematically connected in series, we studied the role of the excitation sequence in spatio-temporal organization of cardiac function. Each model element was represented by a well-verified mathematical model of cardiac electro-mechanical activity. We found that homogeneous chains, consisting of identical elements, respond to non-simultaneous stimulation by generation of complex spatio-temporal heterogeneities in element deformation. These are accompanied by the establishment of marked gradients in local electro-mechanical properties of the elements (heterogeneity in action potential duration, Ca2+ transient characteristics and sarcoplasmic reticulum Ca2+ loading). In heterogeneous chains, composed of elements simulating fast and slow contracting cardiomyocytes from different transmural layers, we found that only activation sequences where stimulation of the slower elements preceded that of faster ones gave rise to optimization of the system's electro-mechanical function, which was confirmed experimentally. Based on the results obtained, we hypothesize that the sequence of activation of cardiomyocytes in different ventricular layers is one of the key factors of spatio-temporal organization of myocardium. Moreover, activation sequence and regional differences in intrinsic electro-mechanical properties of cardiac muscle must be matched in order to optimize myocardial function.