Cellular model for induction of drip loss in meat

Drip loss from porcine muscle (M. longissimus dorsi) contained high concentrations of K+ (similar to 135 mM) and organic osmolytes, for example, taurine (similar to 15 mM), as well as significant amounts of protein (similar to 125 mg.mL(-1)). Thus, the drip reflects release of intramuscular components. To simulate events taking place at the time of slaughter and leading to release of osmolytes and subsequent formation of drip loss, C2C12 myotubes were exposed to anoxia and reduction in pH (from 7.4 to 6.0). Anoxia and acidification increased the cellular Ca2+ Concentration ([Ca2+](i)) at a rate of 22-32 nM.min(-1). The anoxia-induced increase in [Ca2+], was mainly due to influx via sarcolemmal Na+ channels. As mammalian cells swell and release lysophospholipids during anoxia, C2C12 cells and primary porcine muscle cells were exposed to either hypotonic shock or lysophosphatidylcholine (LPC) and the release of taurine was followed. The swelling-induced taurine efflux was blocked in the presence of the anion channel blocker (DIDS), the 5-lipooxygenase inhibitors (ETH 615-139 and NDGA) but unaffected by the presence of vitamin E. In contrast, the LPC-induced taurine release was unaffected by DIDS but abolished by antioxidants (butylated hydroxytoluene and vitamin E). Thus, stress-induced taurine release from muscles may precede by two different mechanisms, one being 5-lipooxygenase dependent and the other involving generation of reactive oxygen species. A model for the cellular events, preceding formation of drip in meat, is presented.