Effect of Changes in Food Consistency on NADH-Ubiquinone Oxidoreductase Activity and Levels of mRNA for ND1, 51kDa, 75kDa and Myosin Heavy Chain Isoforms in Two Different Portions of Rat Masseter Muscle

Abstract

We investigated the effect of a change in food consistency on properties of the masseter muscle in 3-week-old rats fed a soft diet for 9 weeks (Group S) and fed a soft diet for 5 weeks followed by a hard diet for 4 weeks (Group S-H). The NADH-O2 oxidoreductase activity, levels of mRNAs transcribed from genes encoding NADH-ubiquinone oxidoreductase (Complex I: ND1, 51kDa, and 75kDa) and myosin heavy chain (MyHC) isoforms and the phenotype of the muscle fibers were measured in the superficial and deep portions of the muscle. In the period from 8 weeks to 12 weeks of age, NADH-O2 oxidoreductase enzyme activity in both the superficial and deep portions of the muscle showed similar patterns in Group S and Group S-H. In contrast, the ND1, 51kDa and 75kDa mRNA levels in the superficial and deep portions of the masseter muscle in the Group S-H were higher than those of Group S in the 12-week-old rats, except for the 51kDa mRNA in the superficial portion of the masseter muscle. MyHC-IIa and MyHC-IId/x mRNA levels in the superficial portion of the masseter muscle were higher in the Group S-H than in the Group S. These observations suggest that short-term feeding stress such as the transition from a soft diet to a hard diet causes changes in oxidative metabolism, in mRNA levels for the Complex I components ND1 and 75kDa, and the mRNA levels for the MyHC isoforms IIa and IId/x in the superficial portion of rat masseter muscle, but no changes in the composition of muscle fiber types.