Immunolabelling for VDAC, the mitochondrial voltage-dependent anion channel, on sarcoplasmic reticulum from amphibian skeletal muscle.

Patch-clamp studies of ion channels in the sarcoball membrane, a relatively pure preparation of sarcoplasmic reticulum, had earlier revealed a high-conductance anion channel with some properties similar to the mitochondrial voltage-dependent anion channel (VDAC). Using post-embedding immunolabelling, the presence of VDAC was investigated in sarcoball preparations from the semitendinosus muscle of the cane toad Bufo marinus. As expected, the outer membrane of mitochondria found within the interior of skinned fibres was decorated with gold label. Surprisingly, sarcoplasmic reticulum membrane was also labelled. The sarcoball membranes, which could arise from either the sarcoplasmic reticulum or from mitochondria, were also labelled. These results indicate the presence of a VDAC-like protein in the sarcoplasmic reticulum.