ROCK, J; FAULKNER, L; WHITELEY, N; University of Wales, Bangor: Does temperature acclimation affect muscle function in marine crustaceans via changes in molecular diversity?

Temperature can have a profound molecular and physiological effect on muscle performance in ectotherms. In this study of a marine amphipod (Gammarus duebeni), we have examined the specific effect of acclimation temperature on 1) actin-activated myosin ATPase activity, and 2) molecular variation in two hypervariable loops of the myosin heavy chain gene. Specifically, we have focused on the S1 domain loops 1 and 2, which influence ATP binding/hydrolysis, sliding velocity and actin-activated Mg²⁺-ATPase activity. Wild G. duebeni were acclimated to 5 or 23°C for 3 weeks. For both acclimation groups, ATPase activities in fast muscle fibres increased at similar rates with the incubation temperature of the assay (Q₁₀ 1.8). However, ATPase activities at each incubation temperature were 30% lower in the 5°C rather than the 23°C group. Collectively, these results show functional differences in myosins after temperature acclimation, even though the myosins do not fully compensate for the temperature change. Differences in sequence length, amino acid composition, and charge are analysed in relation to their potential effect on ATP hydrolysis and, notably, actinomyosin interactions and over-all muscle function. Further comparisons are made with molecular structure and function in G. duebeni populations from varying natural thermal environments.