Abstract
The isometric twitch properties of papillary muscles from hearts of 30- to 53-day-old cardiomyopathic hamsters (BIO 14.6) were studied before and after exposure to the cardiac glycoside, ouabain. The diseased tissue was weakly responsive to ouabain (3 to 100 microM), as compared to a more appreciable positive inotropic response in papillary muscle of similarly aged normal hamsters (BIO F1B). These data suggest that the activity of Na+,K+-ATPase is attenuated in the diseased sarcolemma. Pretreatment with the beta-adrenoceptor agonist, isoproterenol (0.1 microM), slightly increased the sensitivity of normal muscle to ouabain, however the response of myopathic muscle was greatly enhanced. These findings may be of significance to the genesis of cellular calcium overload hypothesized to be involved in the necrosis and degeneration of heart cells in this animal model of genetic cardiomyopathy.
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