In vitro studies of mitochondrial and sarcoplasmic reticulum function in muscle of stress susceptible pigs.

Seven stress susceptible (SS) and six stress resistant (SR) pigs were identified by response to halothane anesthesia. Mitochondria and heavy sarcoplasmic reticulum fragments were isolated from biopsies of the semimembranosus muscle. The muscle pH was significantly lower (P<.01) in the SS pigs compared to the SR pigs at biopsy. The mitochondrial respiratory traits, state 3 and state 4 respiration, respiratory control index and ADP/0 ratio, however, were not significantly different (P>.05) for the two groups of pigs. Mitochondrial ATPase activity and sarcoplasmic reticulum Mg-ATPase activity were not significantly different (P>.05) for the muscles of SS and SR pigs. The MgCa-ATPase activity of sarcoplasmic reticulum isolated from the muscle of SS pigs was significantly higher (P<.01) than that observed for SR pigs. No differences (P>.05) in mean values for pH, percentage reflectance and percentage transmission values of the longissimus muscle were observed between the SS and SR pigs, but greater variation in values for these traits was observed in muscle from SS pigs. (