EFFECT OF TAURINE AND METHIONINE ON SARCOPLASMIC RETICULAR CA2+ TRANSPORT AND PHOSPHOLIPID METHYLTRANSFERASE ACTIVITY

Perfusion of rat hearts with buffer containing 300 mu M L-methionine l ed to a decrease in Ca2+-induced Ca2+ release in sarcoplasmic reticulu m (SR) but an increase in calcium-independent Ca2+ release from juncti onal SR. These effects of L-methionine were not altered by exposure of the hearts to high levels of extracellular taurine, but changes in th e size of the intracellular taurine pool appear to modulate calcium tr ansport in SR through two mechanisms. First, millimolar concentrations of taurine can directly promote release of calcium from Ca-45(2+)- lo aded junctional SR vesicles. Second, taurine serves as an inhibitor of SR phospholipid methyltransferase, an enzyme that appears to be respo nsible for methionine-mediated loss in Ca22+-induccd Ca2+ release acti vity and promotion of Ca2+-independent Ca2+ release. The data imply th at modulation of the intracellular taurine pool may affect cellular ca lcium homeostasis and myocardial contractile function. This may be imp ortant in development of the cardiomyopathy linked to taurine deficien cy.