Calcium sensitivity of isometric tension in intact papillary muscles and chemically skinned trabeculae in different models of hypertensive hypertrophy

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Abstract
Study objective – The aim was to examine the contractile state, the inotropic response to [Ca2+]e and the Ca2+ sensitivity of the contractile proteins in different models of hypertensive hypertrophy in an early stage of evolution (3–4 weeks). Design – Renal hypertension was induced by placing a silver clip around the left renal artery. The contralateral kidney was either removed (1K-1C) or left untouched (2K-1C). Hypertension through sodium overload was produced by administration of deoxycorticosterone and 1% NaCl drinking water. (DOCA rats). Active and passive length-tension curves were performed to evaluate basal contractility at Lmax and passive stiffness of cardiac muscle. The inotropic responsiveness to [Ca2+]e and the Ca2+ sensitivity of the contractile proteins were also evaluated. Experimental material – Papillary muscles and skinned trabeculae from the left ventricle of male Wistar hypertensive and age matched normotensive rats were used. Measurements and results – Cardiac hypertrophy was similar in all hypertensive groups. In 2K-1C and 1K-1C rats, basal contractility was not significantly different from controls. In DOCA rats, developed tension and time to peak tension (TTP) were significantly greater than controls. The inotropic response to [Ca2+]e was depressed in 2K-1C and increased in DOCA rats. In DOCA rats, increasing [Ca2+]e produced an increase in TTP greater than in controls. No differences were detected in muscle passive stiffness or in Ca2+ sensitivity of the contractility proteins among the different groups. Conclusions – In the earlier stages of hypertensive hypertrophy, differences in basal contractile state and/or inotropic responsiveness appear to be more related to the initiating cause of hypertensive hypertrophy than to the degree of hypertrophy itself. These differences cannot be attributed to changes in Ca2+ sensitivity of the contractile system.

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