Differences in the Expression of MHC Isoforms in Single Muscle Fibers After A18 wk Cold Adaptaionin Hamsters

Abstract

PURPOSE: The purpose of this study was to determine alterations in the expression of MHC isoforms in single muscle fibers after a 18 wk cold exposure in hamsters. METHODS: Ten Golden hamsters (Mesocrietus auratus), aged 15∼17 weeks were randomly assigned to two groups: control group (n=5, CO) and cold exposed group (n=5, CE). The CE group was exposed to cold temperature at 5°C±1 for 18 weeks while the CO group was housed for 18 weeks at 22°C±2. Electrophoretic analyses were performed in single muscle fibers of the vastus intermeidus (VI) muscle (n=50 per muscle) as well as in whole VI muscle. RESULTS: Significant increases in body weight, heart weight, heart rate and body temperature were observed in CE group compared to CO group. Interestingly, blood glucose was significantly lowered in CE as compared to CO (42.2±18.6 vs. 97.4±22.2mg/ dL). MHC type IIA disappeared completely in whole muscle (VI) in CE whereas CO possessed 26% in type IIA. However, CE showed significant increases in MHC type IIX and type IIB as compared to CO. As for single fiber analyses, co-expression of MHC type IIA and IIX was significantly increased in CO, but type IIX and IIB was significantly highly co-expressed in CE, suggesting that type IIX is a dominant isoform in CE. CONCLUSIONS: It is plausible that the transformed MHC isoform type IIX is a muscle adaptation to cold environment, yields metabolic efficiency.