REMOVAL OF MG2-A( INHIBITION OF CARDIAC RYANODINE RECEPTOR BY PALMITOYL COENZYME)

Ca-45(2+) fluxes and planar bilayer recordings indicated that the fatt y acid metabolite palmitoyl coenzyme A, but not free coenzyme A or pal mitic acid, stimulated the cardiac ryanodine receptor channel of pig h eart sarcoplasmic reticulum. Palmitoyl CoA reactivated channels inhibi ted by concentrations of cytoplasmic free Mg2+ in the physiological ra nge. Reactivation by palmitoyl CoA in the presence of Mg2+ was stimula ted by myoplasmic free Ca2+ in the micromolar range. Acyl coenzyme A d erivatives may be utilized by cardiac muscle cells to compensate for t he severe Mg2+ inhibition of ryanodine receptors which would otherwise leave Ca2+ stores unresponsive to Ca2+ and to other cytosolic ligands involved in signal transduction.