Skeletal Muscle Histidine Containing Dipeptide Contents are Increased in Freshwater Turtles (Chrysemys picta bellii) with Cold-Acclimation

Abstract

Freshwater turtles found in higher latitudes can experience extreme challenges to acid-base homeostasis while overwintering, due to a combination of cold temperatures along with the potential for environmental hypoxia. Histidine containing dipeptides (HCDs; carnosine, anserine and balenine) may facilitate pH regulation in response to these challenges, through their role as pH buffers. We measured the HCDs content of three tissues (liver, cardiac muscle and skeletal muscle) from the anoxia-tolerant painted turtle (Chrysemys picta bellii) acclimated to either 3 or 20{degrees}C. HCDs were detected in all tissues, with the highest content shown in the skeletal muscle. Turtles acclimated to 3{degrees}C had more HCD in their skeletal muscle than those acclimated to 20{degrees}C (carnosine = 20.8{+/-}4.5 vs 12.5{+/-}5.9 mmol{middle dot}kg DM-1; ES = 1.59 (95%CI: 0.16 - 3.00), P = 0.013). The higher HCD content observed in the skeletal muscle of the cold-acclimated turtles suggests a role in acid-base regulation in response to physiological challenges associated with living in the cold, with the increase possibly related to the temperature sensitivity of carnosines dissociation constant and buffering power of the skeletal muscle during anoxic submergence. HighlightsO_LIpH regulation is a major challenge for overwintering freshwater turtles. C_LIO_LIHistidine containing dipeptides are important intracellular buffers. C_LIO_LITurtles acclimated to 3{degrees}C had higher HCD content than those at 20{degrees}C. C_LIO_LIHCDs may be important pH regulators in cold-acclimated turtles. C_LI