Regulation of calcium transport in drug-induced taurine-depleted hearts.

Drug-induced taurine depletion of rat heart led to the accumulation of free CoA, free carnitine and long-chain acylcarnitine, but a small decrease in long-chain fatty acyl-CoA. Although elevations in total tissue long-chain acylcarnitine levels have been linked to defective membrane function and the association of long-chain acylcarnitines with extramitochondrial membranes, these effects were absent in isolated sarcoplasmic reticulum prepared from taurine-depleted hearts. In contrast to the sarcoplasmic reticulum data, taurine depletion was associated with a significant decrease in ATP-dependent calcium uptake by isolated sarcolemmal vesicles. The major effect of taurine depletion on the sarcolemma was a 2-fold decrease in both the Vmax of calcium transport and the activity of the Ca2+ -stimulated ATPase. Sarcolemmal vesicles prepared from taurine-depleted hearts also exhibited a decreased capacity to transport calcium in exchange for sodium, although the initial rate of the process was unaffected by taurine depletion. Since incubation of sarcolemma from taurine-depleted hearts with taurine could not overcome the effects of taurine depletion, it was concluded that the effects of taurine were not caused by a direct interaction of it with the calcium pump. Possible mechanisms of taurine action are discussed.