Comparison between isomyosin pattern and contractility of right ventricular myocytes isolated from rats with right cardiac hypertrophy

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Abstract
The contractile properties of single rat cardiac cells isolated from normal and hypertrophied right ventricles have been investigated. These have been correlated with the isoenzyme composition of the whole ventricle. Right cardiac hypertrophy was induced by injecting rats with monocrotaline, an alkaloid which induces severe pulmonary hypertension. Ca2+ ATPase activity and myosin alpha-chain percentage were decreased in the hypertrophied right ventricle as compared with that of control rats. The contraction amplitude and speed of shortening of the isolated cells were measured using an inverted microscope, video camera, and edge detection device. Cells from the hypertrophied ventricle showed a significantly decreased contraction amplitude and speed of shortening in maximally activating concentrations of isoprenaline. A statistically significant correlation existed between myosin alpha-chain percentage and both contraction amplitude and speed of shortening in maximum isoprenaline. This was truc when all cells studied were included, as well as within the hypertrophy group. A similar, although not always statistically significant, correlation was observed when cells were maximally activated with calcium. These results suggest that changes in isomyosin pattern that occur in cardiac hypertrophy produce alterations in contraction amplitude and speed of shortening which can be detected in single cells isolated from the hypertrophied ventricles. Isolated cells appear to give responses representative of the function of the whole heart.