FATTY ACYL-COA ESTERS INDUCE CALCIUM-RELEASE FROM TERMINAL CISTERNAE OF SKELETAL-MUSCLE

The effect of palmitoyl-CoA (PCoA) on Ca2+ fluxes in unfractionated SR , longitudinal tubules (LSR) and terminal cisternae (TC) subfractions, obtained from rabbit fast-twitch skeletal muscles, was investigated. After MgATP-dependent Ca2+ preloading, PCoA released Ca2+ from unfract ionated SR and TC, but not from LSR. Both the extent and the rate of P CoA-induced Ca2+ release from TC were increased in a dose-dependent ma nner the half-maximal effect being attained at [PCoA] of approximately 6 mu M. Ruthenium red, a Ca2+ release channel blocker, completely inh ibited PCoA-induced Ca2+ release, whereas caffeine, a Ca2+ release cha nnel agonist, depleted TC of Ca2+ and prevented the PCoA action. Scatc hard plot analysis of [H-3]-ryanodine binding showed that PCoA increas ed the affinity without affecting B-max. The action of PCoA was mimick ed by a The present results indicate that PCoA interacts and opens the Ca2+ release channel (ryanodine receptor) of TC and that the mechanis m of action involves binding rather than hydrolysis.