Heterogeneity of Human Cardiac Muscle Inotropic Response to Stimulation of β1-adrenergic Receptors and Their Expression in Chronic Coronary Heart Disease

Aim. To study the intensity and correlation between the inotropic responses of myocardium in patients with chronic coronary heart disease (CHD) upon stimulation of β1-adrenergic receptors (β1-AR) and the expression levels of these receptors in cardiomyocytes. Materials and methods. Isolated myocardium (fragment of the right atrial appendage) from 46 patients with chronic CHD was obtained during coronary artery bypass grafting. The inotropic response of muscle strips was evaluated in an isometric condition. To affect β1-adrenergic receptors (β1-ARs), norepinephrine (10 –7 M) was used under pre-blockade of α-adrenergic receptors (α-AR). The expression of β1-ARs was determined by Western blotting in the same myocardial samples. Results. It has been established that the myocardium of this cohort of CHD patients demonstrated significant heterogeneity both in terms of the inotropic response to stimulation of β1-adrenergic receptors and the degree of their receptor expression. A significant positive correlation ( r = 0.72; p < 0.001) was observed between the inotropic response of muscle strips and the expression level of β1-ARs in these patients’ myocardium. Conclusion. These findings confirm that the extent of the inotropic response of the myocardium to activation of β1-ARs significantly depends on the number of β1-ARs present when chronic CHD develops. This dependency reflects the degree of cardiac remodeling occurring in this pathology.