X-Message-Number: 24678 From: "Basie" <> Subject: The effects of freezing on organ metabolism Date: Tue, 21 Sep 2004 00:54:53 -0400 ORGAN METABOLISM AND CRYOPROTECTANT SYNTHESIS IN SPRING PEEPERS Pseudacris crucifer Thomas A. Churchill and Kenneth B. Storey ---- SUMMARY The effects of freezing on organ metabolism were monitored over a 36 h time course of freezing at -4 C in spring-collected specimens of a freeze tolerant frog, the spring peeper Pseudacris crucifer. Within 2 min after freezing began, glycogenolysis in liver had been activated as evidenced by elevated levels of hexose phosphates and glucose in the organ. Freezing stimulated a 3.3-fold increase in liver glycogen phosphorylase a activity and a rapid phase of liver glucose production was maintained for at least the first hour of freezing exposure (21 mol.g wet mass-1.h-1), followed by a lower, steady rate of glucose increase of about 3 mol.gwm-1.h-1. Final liver glucose concentration was 141 mol.gwm-1 after 36 h. Correlated with this, changes in the concentrations of hexose phosphates and fructose-1,6-bisphosphate in liver indicated that glucose production was promoted by an inhibitory block on glycolysis at the phosphofructokinase reaction during the rapid phase of glucose production. Other organs accumulated glucose as a cryoprotectant during freezing exposure. Liver energetics were not disrupted during the early phase of freezing but with prolonged freezing (4-36 h) ATP content fell, ADP and AMP increased, and energy charge ([ATP + ADP/2] / [ATP + ADP + AMP]) was reduced from 0.90 in controls to 0.57 after 36 h freezing. Liver metabolism during freezing was supported by fermentative reactions. Anaerobic glycolysis resulted in the accumulation of both lactate and alanine and levels of fermentable free amino acids (aspartate and glutamate) decreased significantly. Changes in free amino acid patterns in skeletal muscle and heart indicated that these also relied upon amino acid fermentation to help support energy metabolism during freezing. In addition, both organs showed small increases in the levels of numerous amino acids suggesting that freezing elevated proteolysis. This study provides new evidence of the importance of amino acids to anuran freezing survival and also demonstrates that the biochemical mechanisms involved in regulating cryoprotectant output, previously described only for the wood frog Rana sylvatica, may be general mechanisms for regulating cryoprotectant pools in all freeze tolerant anurans Churchill, T.A. and Storey, K.B. 1996. Organ metabolism and cryoprotectant synthesis in spring peepers, Pseudacris crucifer. Copeia 196 (3) 517-525. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=24678