PROTEIN PHOSPHATASE TYPE-1 MESSENGER-RNA LEVELS IN RESPONSE TO STARVATION-REFEEDING AND STREPTOZOTOCIN-DIABETES

Levels of the mRNA encoding the catalytic subunit of protein phosphata se type-1 (PP-1(cat)) were reduced in skeletal muscle but not liver in response to short-term (2h) chow refeeding after prolonged (40h) star vation in the rat. This reduction did not appear to be mediated by ins ulin per se since streptozotocin-induced diabetes was associated with a reduction in PP-1(cat) levels in skeletal muscle. It is suggested th at glucose levels may be one factor that modulates skeletal muscle PP- 1(cat) mRNA levels. Despite the changes in PP(-)1(cat) mRNA levels in skeletal muscle, total protein phosphatase I catalytic activity was no t altered by either chow refeeding or streptozotocin-diabetes. By cont rast, although total hepatic PP-1(cat) mRNA levels were not altered in response to chow refeeding, there was a marked reduction in glycogen phosphorylase phosphatase activity in the cytosol but not in the glyco gen/microsomal fraction.