DIFFERENCES IN CONTRACTURE DEVELOPMENT OF VENTRICULAR AND ATRIAL PREPARATIONS OF MAMMALIAN CARDIAC MUSCLE

The influence of external calcium and sodium ions1 on potassium contractures was studied in different isolated preparations of, mammalian cardiac muscle (thin ventricular and atrial trabeculae of calf hearts; guinea-pig papillary muscles). In atrial trabeculae of calf hearts, the effects of external calcium and sodium ions on contractures were the same as in guinea-pig auricles (Scholz 1969a). Raising [Ca]e or reducing [Na]e caused an increase of tension development and a shift of mechanical threshold to lower [K]e. At any given [K]e the amplitude of contractures depended on the ratio Ca/Na2 in the bathing fluid as in frog hearts (Lüttgau and Niedergerke, 1958). In Na-free solutions contractures developed even without increasing [K]e. Compared to the atrial preparations, however, contractures of ventricular trabeculae of calf hearts and of guinea-pig papillary muscles showed the following differences. Raising [Ca]e or reducing [Na]e caused a somewhat smaller increase in tension development. In Na-free solutions, no contractures could be observed unless [K]e was increased. At constant [K]e, the amplitude of contractures did not depend on the ratio [Ca]e/[Na]e2. The differences between the mechanical response of atrial and ventricular preparations of mammalian hearts are tentatively explained by some differences in the ultrastructure of both tissues. © 1969 Springer-Verlag.