The sarcoplasmic reticulum Ca2+ pump: inhibition by thapsigargin and enhancement by adenovirus-mediated gene transfer.

The role of the sarcoplasmic reticulum Ca2+ pump in the excitation-contraction coupling of cardiac muscle fibers was evaluated in experiments on SR ATPase inhibition with thapsigargin or, alternatively, on Ca2+ pump enhancement by SR ATPase transgenic expression. We found that thapsigargin, a highly specific and potent inhibitor of the SR ATPase, produces a strong reduction of cytosolic Ca2+ transient and contractile activation in neonatal rat myocytes, in the absence of any other functional effect. On the other hand, Ca2+ pump enhancement by ATPase transgenic expression affects dramatically Ca2+ transient and twitches, resulting in shorter duration and more rapid decay rates. Of particular interest is gene transfer mediated by recombinant adenovirus vectors under control of a cell-specific promoter, resulting in transgenic expression of all myocytes in culture, and no expression in fibroblasts.