Rapamycin inhibits activation of ryanodine receptors from skeletal muscle by the fatty acyl CoA-acyl CoA binding protein complex

We previously showed (Fulceri et al., Biochem. J. 325, 423, 1997) that the fatty acyl CoA ester palmitoyl CoA (PCoA) complexed with a molar excess of its cytosolic binding protein (ACBP) causes a discrete Ca2+ efflux or allow s Ca2+ release by suboptimal caffeine concentrations, in the Ca2+-preloaded terminal cisternae fraction (TC) from rabbit skeletal muscle, by activatin g ryanodine receptor Ca2+ release channels (RyRC), We show here that both e ffects were abolished by pretreating TC with the FKBP12 ligand rapamycin (2 0 mu M). Moreover, rapamycin reversed the Ca2+ release induced by combined treatment with 3 mM caffeine and the PCoA-ACBP complex. Rapamycin also redu ced the Ca2+-releasing activity by PCoA alone. Under the above experimental conditions, rapamycin removed FKBP12 from the TC membranes, as revealed by Western blot analysis. We conclude that FKBP12 associated with RyRC in the TC membrane participates in the activation of the Ca2+ channel by fatty ac yl CoA esters, (C) 1999 Academic Press.