Time course for cryoprotectant synthesis in the freeze-tolerant chorus frog, Pseudacris triseriata

Increases in liver glycogen phosphorylase activity, along with inhibition o f glycogen synthetase and phosphofructokinase-1, are associated with elevat ed cryoprotectant (glucose) levels during freezing in some freeze-tolerant anurans. In contrast, freeze-tolerant chorus frogs, Pseudacris triseriata, accumulate glucose during freezing but exhibit no increase in phosphorylase activity following 24-h freezing bouts. In the present study, chorus frogs were frozen for 5- and 30-min and 2- and 24-h durations. After freezing, g lucose, glycogen, and glycogen phosphorylase and synthetase activities were measured in leg muscle and liver to determine if enzyme activities varied over shorter freezing durations, along with glucose accumulation. Liver and muscle glucose levels rose significantly (5-12-fold) during freezing. Glyc ogen showed no significant temporal variation in liver, but in muscle, glyc ogen was significantly elevated after 24 h of freezing relative to 5 and 30 min-frozen treatments. Hepatic phosphorylase a and total phosphorylase act ivities, as well as the percent of the enzyme in the active form, showed no significant temporal variation, following freezing. Muscle phosphorylase a activity and percent active form increased significantly after 24 h of fre ezing, suggesting some enhancement of enzyme function following freezing in muscle. However, the significance of this enhanced activity is uncertain b ecause of the concurrent increase in muscle glycogen with freezing. Neither glucose 6-phosphate independent (I) nor total glycogen synthetase activiti es were reduced in liver or muscle during freezing. Thus, chorus frogs disp layed typical cryoprotectant accumulation compared with other freeze-tolera nt anurans, but freezing did not significantly alter activities of hepatic enzymes associated with glycogen metabolism. (C) 2000 Elsevier Science Inc. All rights reserved.