Liver protein kinase A activity is decreased during the late hypoglycemic phase of sepsis

Changes in protein kinase A (PKA, or cAMP-dependent protein kinase) activit y in the rat liver during different metabolic phases of sepsis were investi gated. Sepsis was induced by cecal ligation and puncture (CLP). Experiments were divided into 3 groups: control, early sepsis, and late sepsis. Early and late sepsis refer to those animals killed at 9 and 18 h, respectively, after CLP. Hepatic PKA was extracted and partially purified by acid precipi tation, ammonium sulfate fractionation, and diethylaminoethyl (DEAE)cellulo se chromatography. PKA was eluted from DEAE-cellulose column with a linear NaCl gradient. Two peaks of PKA, type I (eluted at low ionic strength) and type II (eluted at high ionic strength), were collected and their activitie s were determined on the basis of the rate of incorporation of [gamma-(32)- P]ATP into histone. The results show that during early sepsis, both type I and type II PKA activities remained unchanged. During late sepsis, type I P KA activity was decreased by 40.7-53.6%, whereas type II PKA activity was u naffected. Kinetic analysis of the data on type I PKA during the late phase of sepsis reveals that the V-max (maximal velocity) values for ATP, cAMP, and histone were decreased by 40.7, 53.6, and 47.3%, respectively whereas t he K-m (substrate concentration required for half-maximal enzymatic activit y) values for ATP, cAMP, and histone were unaltered. These data indicate th at type I PKA was inactivated during the late hypoglycemic phase of sepsis in the rat liver. Because PKA-mediated phosphorylation plays an important r ole in the regulation of hepatic glucose metabolism an inactivation of PKA may contribute to the development of hypoglycemia during the late phase of sepsis.