Metabolic responses to freezing by organs of hatchling painted turtles Chrysemys picta marginata and C. p. bellii

Abstract

Organ-specific metabolic responses to freezing were monitored over the course of 4 h exposure to freezing at −4 °C for autumn-collected hatchlings of midland (Chrysemys picta marginata) and western (Chysemys picta bellii) painted turtles. Both subspecies accumulated glucose and lactate in seven organs during freezing for possible use as cryoprotectants. Overall levels of both were higher in C. p. bellii than in C. p. marginata, with glucose ranging up to 16 μmol/g wet weight and lactate up to 25 μmol/g in C. p. bellii organs. Glucose accumulation by C. p. bellii organs appeared to be initiated during prefreeze cooling, whereas glucose production in C. p. marginata was triggered by the initiation of freezing; this difference may explain the higher overall accumulations of both glucose and lactate in C. p. bellii organs. Glucose content in most organs declined over the course of the 4-h freezing exposure, suggesting that the main function of the sugar may be as the substrate for lactate production. Analysis of changes in the levels of glycolytic intermediates in liver revealed an accumulation of glucose-6-phosphate, indicating activation of liver glycogenolysis during freezing. An increase in liver fructose-6-phosphate and a decrease in fructose-1,6-bisphosphate concentrations over the course of freezing were consistent with an inhibition of liver phosphofructokinase that would support glucose export to other organs.