Use of stable isotope labelling to study protein degradation in chick embryonic skeletal muscle cell cultures

stable isotope labelling method was developed for use in identifying compounds that affect the rate of proteolysis in primary embryonic chick skeletal muscle cell cultures. Effects of leupeptin and calpain inhibitors I and II on proteolysis in 8 d-old cell cultures was determined by prelabelling cells with natural leucine and measuring its release into culture medium containing ;Cycloheximide was used to block protein synthesis in muscle cultures to ascertain if the relative rates of proteolysis measured reflected absolute rates. All stable isotope labelling was used with ;Lastly the affect of leupeptin and calpain inhibitors I and II on the growth of chicks was examined. 7-day-old male White Leghorn chicks were given daily intraperitoneal inhibitor injections for 7 days. In experiments 1 and 2, inhibitors were administered in a 25% ethanol/75% saline carrier. At doses of 2.0 or 20.0 mg/kg body weight, calpain Inhibitors I and II had no effect on gain or feed efficiency, while leupeptin-injected chicks gained more than the control chicks (P...