Changes in proteinase/proteinase inhibitor levels in rat skeletal muscle tissue during diabetes and fasting

The skeletal muscle content of three rat proteinase inhibitors, a 1-proteinase inhibitor, contrapsin and a 1-cysteine proteinase inhibitor was measured by immunochemical techniques following streptozotocin-induced diabetes. When compared with normal rats, a 1-cysteine proteinase inhibitor and a 1-proteinase inhibitor levels remained essentially unchanged, whereas the content of rat contrapsin was reduced by nearly 80% after the onset of diabetes. Similarly, fasting of rats for three days resulted in a lowering of the levels of contrapsin in skeletal muscles. Under these conditions, levels of chymotrypsin-like activity (chymase) were increased by 150%, whereas the content of the trypsin-like, neutral proteinase was unchanged. Kinetic studies in vitro with Tosyl-Gly-Pro-Arg-4-nitroanilide as substrate showed no inhibition of the trypsin-like proteinase by a 1-proteinase inhibitor, while contrapsin inhibited the enzyme with a Ki value of 40nM. The changing pattern of these proteinases and their potential inhibitors (chymase/a 1-proteinase inhibitor and trypsin-like proteinase/contrapsin) may be a factor contributing to muscle wasting as observed in diabetes and fasting.