FATTY ACYL-COA ACYL-COA-BINDING PROTEIN COMPLEXES ACTIVATE THE CA2-MUSCLE SARCOPLASMIC-RETICULUM( RELEASE CHANNEL OF SKELETAL)

We previously reported that fatty acyl-CoA esters activate ryanodine r eceptor/Ca2+ release channels in a terminal cisternae fraction from ra bbit skeletal muscle [Fulceri, Nori, Gamberucci, Volpe, Giunti and Ben edetti (1994) Cell Calcium 15, 109-116]. Skeletal muscle cytosol conta ins a high-affinity fatty acyl-CoA-binding protein (ACBP) [Knudsen, Ho jrup, Hansen, H.O., Hansen, H. F. and Roepstorff(1989) Biochem. J. 262 , 513-519]. We show here that palmitoyl-CoA (PCoA) in a complex with a molar excess of bovine ACBP causes a discrete Ca2+ efflux or allows C a2+ release from the Ca2+-preloaded terminal cisternae fraction by sub -optimal caffeine concentrations. Both effects were abolished by eleva ting the free [Mg2+] in the system, which inhibits the Ca2+ release ch annel activity. Sensitization towards caffeine was a function of both the concentration of the complex and the [PCoA]-to-[ACBP] ratio. In al l experimental conditions the calculated free [PCoA] was no more than 50 nM, and such concentrations by themselves were inactive on Ca2+ rel ease channels. The K-D for PCoA binding was approx. 2 nM for bovine an d yeast ACBP, and slightly higher (8 nM) for rat ACBP. The PCoA-rat AC BP complex behaved in the same manner as the PCoA-bovine ACBP complex, whereas the ester complexed with yeast ACBP was more active in activa ting/sensitizing Ca2+ efflux. A non-hydrolysable analogue of PCoA boun d to (bovine) ACBP also sensitized the Ca2+ release channel towards ca ffeine. These findings indicate that fatty acyl-CoA-ACBP complexes eit her interact directly with one or more components in the terminal cist ernae membranes or, through interaction with the component(s), donate the fatty acyl-CoA esters to high-affinity binding sites of the membra ne, thus affecting (and possibly regulating) Ca2+ release channel acti vity.