Characterization of rat porin isoforms: cloning of a cardiac type-3 variant encoding an additional methionine at its putative N-terminal region.

In vivo, the outer mitochondrial membrane presents a restriction of diffusion for ADP in heart and slow twitch skeletal muscles, but not in fast twitch skeletal muscle. Mitochondrial porins constitute the main pathway for the transit of metabolites across the outer mitochondrial membrane. We decided, therefore, to characterize, by cloning, rat heart VDAC and to follow their expression in different striated muscles. We cloned three isoforms, one being HVDAC1-like porin (RVDAC1) whereas the other two are MVDAC3-like porins (RVDAC3 and RVDAC3v). These three isoforms are ubiquitously expressed among striated muscles. RVDAC3v differs from RVDAC3 by one additional amino acid, a Met, located between Val39 and Glu40 in RVDAC3 sequence. This study constitutes a first step in order to further characterize striated muscle porin isoforms.