VDAC PORIN IS PRESENT IN SARCOPLASMIC-RETICULUM FROM SKELETAL-MUSCLE/

In this study we demonstrate the existence of a protein with propertie s of the voltage-dependent anion channel (VDAC) in the sarcoplasmic re ticulum (SR) using multiple approaches as summarized in the following: (a) 35 and 30 kDa proteins in different SR preparations, purified fro m other membranal systems by Ca2+/oxalate loading and sedimentation th rough 55% sucrose, cross-react with four different VDAC monoclonal ant ibodies, (b) Amino acid sequences of three peptides derived from the S R 35 kDa protein are identical to the sequences present in VDAC1 isofo rm, (c) Similar to the mitochondrial VDAC, the SR protein is specifica lly labeled by [C-14]DCCD, (d) Using a new method, a 35 kDa protein ha s been purified from SR and mitochondria with a higher yield for the S R, (e) Upon reconstitution into a planar lipid bilayer, the purified S R protein shows voltage-dependent channel activity with properties sim ilar to those of the purified mitochondrial VDAC or VDAC1/porin 31HL f rom human B lymphocytes, and its channel activity is completely inhibi ted by the anion transport inhibitor DIDS and about 80% by DCCD, We al so demonstrate the translocation of ATP into the SR lumen and the phos phorylation of the luminal protein sarcalumenin by this ATP, Both ATP translocation and sarcalumenin phosphorylation are inhibited by DIDS, but not by atractyloside, a blocker of the ATP/ADP exchanger, These re sults indicate the existence of VDAC, thought to be located exclusivel y in mitochondria, in the SR of skeletal muscle, and its possible invo lvement in ATP transport, Together with recent studies on VDAC multico mpartment location and its dynamic association with enzymes and channe ls, our findings suggest that VDAC deserves attention and consideratio n as a protein contributing to various cellular functions.