The mechanism of the adrenergic stimulation of taurine influx in the heart.

The mechanism of isoproterenol-stimulated taurine uptake was examined in the perfused rat heart. Hearts were perfused by the Langendorff technique in a non-recirculating system, while heart rate and contractile force were determined continuously. Perfusion with inotropic concentrations of glucagon stimulated the uptake of [3H]taurine. If the positive inotropic response to isoproterenol was blocked with verapamil, a calcium antagonist, the uptake of taurine was still stimulated. This indicates that inotropy per se, or calcium influx are not involved in the modulation of taurine influx, but that influx rats is responding to cell cyclic AMP levels. The lack of effect of the positively inotropic ionophores monensin and A23187 and the negatively inotropic ionophore valinomycin is in agreement with this conclusion. Taurine decreased calcium binding to cardiac sarcolemma by 31% at 1 mM concentration and 80% at 5 mM.