Comparison of the contractile performance of the hypertrophied myocardium from spontaneous hypertensive rats and normotensive infarcted rats.

The sarcoplasmic reticulum (SR) exerts a key role on the excitation-contraction coupling process in the myocardium. Since the relation between the volume of cellular organelles, such as SR, and the sarcolemmal area of myocytes is not uniform in myocardial hypertrophy of different etiologies, we compared the contractile performances of hypertrophied left ventricular papillary muscles from rats with pressure overload and with volume overload. Hemodynamically compensated spontaneous hypertensive rats (SHR, 3 months old, systolic blood pressure = 189 ± 4 mmHg, n = 8) and Wistar rats with healed (30 days) myocardial infarction (MI, n = 7) produced by ligation of the left coronary artery were used. Results were compared with age-matched Wistar control (CON) rats (n = 13). Force (F), corrected to muscle cross-sectional area (g/mm2), and dF/dt were recorded in muscles contracting isometrically and stretched to Lmax. The inotropic response to increasing extracellular Ca2+ concentrations (1.25 to 5.0 mM) was compar...