The role of integrin degradation in post-mortem drip loss in pork.

Cell membranes are attached to the cell body by two major types of adhesion complexes, integrin-containing focal adhesions and the dystrophin/dystroglycan complex of proteins. In this study, we used samples with known and varying rates of drip channel formation to determine whether the time frame of formation of the channels correlated with the rate of cell/membrane adhesion protein degradation. Our results indicate that the degradation of the β1-chain of integrin, the portion of the protein involved in adhesion of the cell membrane to the cytoskeleton, temporally correlates to the opening of drip channels in pork, while dystrophin degradation does not. Additionally, this degradation may be due to activation of calpains at the site of adhesion plaques. Previous work has indicated that calpains can degrade the β-chain of integrins in vitro. We find that m-calpain is co-localized with β1-integrin at the cytoplasmic surface of the cell membrane in plaque-like structures and is active in these regions post-mortem. Inhibition of calpains not only results in inhibition of integrin degradation, but blocks the opening of drip channels. Therefore, the opening of drip channels in pork may well be due to the degradation of integrin proteins on the cell surface by calpains.