Cyclic GMP-induced reduction in cardiac myocyte function is partially mediated by activation of the sarcoplasmic...

We tested the hypothesis that the mechanism through which cyclic GMP reduces cardiac function is mediated by activation of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA). Cardiac myocytes were isolated from New Zealand white rabbits (n = 11). Individual ventricular cells were stimulated by electrical field stimulation. The maximal rate of cell shortening and percentage shortening were measured with a video edge detector. Thapsigargin (10(-8) mol/l) was used as a specific inhibitor of SERCA. When 8-bromo-cyclic GMP (8-Br-cGMP, 10(-7, -6, -5) mol/l) was added to cells, the maximal rate of myocyte shortening (R(max), microm/s) and percentage shortening were both decreased in a concentration-dependent manner. R(max) decreased 27% from 117 +/- 12 at baseline to 85.2 +/- 13 when 10(-5) mol/l of 8-Br-cGMP was present, and percent shortening was reduced 28% from 6.0 +/- 0.5 to 4.3 +/- 0.5%. Thapsigargin (10(-8) mol/l) increased the maximal rate of myocyte shortening and percent shortening. Addition of thapsigargin prior to 8-Br-cGMP reduced the negative effects of cGMP on myocyte function. The percent shortening decreased only 11% and R(max) decreased 14% with 10(-5) mol/l 8-Br-cGMP, which was not significant. Cyclopiazonic acid, another SERCA inhibitor, was also used to test whether 8-Br-cGMP reduced myocyte function through SERCA. The results were similar to those when thapsigargin was used. These results indicated that the cyclic GMP-induced reduction in cardiac myocyte function was partially mediated through the action of the sarcoplasmic reticulum Ca(2+)-ATPase.