The effect of mechanical loading on the response of rat ventricular myocytes to acidosis

The effect of mechanical loading on the negative inotropic effect of acidosis in isolated rat ventricular myocytes was investigated. The mechanical loading of the myocytes was changed by attaching carbon fibres to the ends of the cell. To monitor intracellular Ca2+ and Na+ concentrations, cells were loaded with fluorescent dyes (fura-2 for Ca2+ and SBFI for Na+) using the acetoxymethyl (AM) esters. Mechanical loading reduced cell shortening by 73.0 +/- 3.5% (mean +/- S.E.M., n = 16) and abbreviated the time course of contraction. CO2-induced acidosis caused a rapid decrease in contraction followed by a slow partial recovery. The percentage changes in contraction were not significantly different in mechanically loaded and unloaded conditions. Mechanical loading had little effect on the time course of contraction during acidosis. Changes in intracellular Ca2+ and Na+ concentrations during acidosis were unaffected by mechanical loading. The mechanical loading conditions of a region of the heart can be modified by ischaemia and the subsequent acidosis. Our results suggest that the response of cardiac muscle to acidosis is not markedly modified by such changes in mechanical loading.