Acute effects of insulin and glucagon on hepatic casein kinase 2 in adult fed rats: Correlation of the effects on casein kinase 2 with the changes in glycogen synthase activity

Abstract

Administration of insulin to adult fed rats caused an inactivation of hepatic casein kinase 2 as determined by the decrease in the activity ratio measured at a low (0.1 mg/ml) and a high (1.0 mg/ml) concentration of β-casein. Maximal inactivation occurred 45 min after injection and the dose for half-maximal effect was 44 μg/kg. The effect of insulin was due to an increase in the apparent K m value for the protein substrate but the magnitude of the effect depended on the substrate used, decreasing in the order β-casein > glycogen synthase ⪢ whole casein. The activation of casein kinase 2 by glucagon (M. Pérez, J. Grande, and E. Itarte (1988) FEBS Lett. 238, 273–276) was also more marked with β-casein and glycogen synthase than with whole casein. A good correlation was observed between the time- and dose-dependent activation of glycogen synthase and inactivation of casein kinase 2 promoted by insulin. Similarly, the inactivation of glycogen synthase by glucagon correlated with the activation of casein kinase 2 caused by this hormone. The possible involvement of casein kinase 2 on the mechanism(s) through which these hormones control hepatic glycogen synthase is discussed.