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 a cidosis in isolated rat ventricular myocytes was investigated. The mec hanical loading of the myocytes was changed by attaching carbon fibres to the ends of the cell. To monitor intracellular Ca2+ and Nai concen trations, 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 rec overy. The percentage changes in contraction were not significantly di fferent in mechanically loaded and unloaded conditions. Mechanical loa ding had little effect on the time course of contraction during acidos is. Changes in intracellular Ca2+ and Na+ concentrations during acidos is were unaffected by mechanical loading. The mechanical loading condi tions of a region of the heart can be modified by ischaemia and the su bsequent acidosis. Our results suggest that the response of cardiac mu scle to acidosis is not markedly modified by such changes in mechanica l loading.