Calcium regulation by the low-affinity taurine binding sites of cardiac sarcolemma
Chovan, J.P.; Kulakowski, E.C.; Sheakowski, S.; Schaffer, S.W.
Molecular Pharmacology 17(3): 295-300
1980
ISSN/ISBN: 0026-895X PMID: 7393210 Document Number: 157709
Several lines of evidence are presented indicating that taurine binding to the low-affinity sites of rat cardiac sarcolemma is responsible for many previously observed, taurine-mediated pharmacological effects. Verapamil inhibits taurine binding to the cell membrane in a dose-dependent manner. Verapamil reverses taurine enhancement of Ca2+ binding to the sarcolemma at concentrations at which verapamil itself has no significant effect on Ca2+ binding. Maximal reversal of the negative inotropic effect of both low Ca2+ and verapamil perfusion occurs at taurine concentrations above the apparent K0.5 of the low-affinity sites. Hypotaurine is a potent inhibitor of taurine binding to the low-affinity sites and exerts taurine-like pharmacological effects. This is contrasted with 2 less potent inhibitors of taurine binding which possess no significant pharmacological activity. Binding to low-affinity sarcolemmal sites is apparently a fundamental step in the mechanism underlying the actions of taurine on the heart. The possibility that low-affinity taurine binding affects the Na+/Ca2+ exchange system of the sarcolemma is discussed.