Protein kinase activity in liver of heat-acclimated hamsters

Protein kinase activity in incubated liver slices from 35° C heat-acclimated (HA) hamsters was 70% higher than in similar slices from 23°C control (C) hamsters. Adding glucagon to the incubation medium increased protein kinase activity by 65% in slices from C animals, but by only 30% in slices from HA animals. Binding of [³H]cAMP to proteins of a low-speed supernatant fraction of incubated and homogenized slices was 30% lower for HA than for C hamsters. For each acclimation group this binding was reduced 30% by incubation of the slices with glucagon. The activities of phosphorylase kinase, phosphorylase phosphatase, and phosphorylase a in slices incubated with or without glucagon did not differ between groups. Addition of glucagon increased phosphorylase kinase by 30% and phosphorylase a by 40% but caused no change in phosphorylase phosphatase activity. These results suggest that heat acclimation of the hamster increases the amount of a species of liver protein kinase that is different from the one that mediates the effect of glucagon on glycogenolysis.