Human skeletal muscle myosin function at physiological and non-physiological temperatures.
OBJECTIVE
The aim of the study was to assess the function of human skeletal muscle myosin across a wide range of temperatures, including physiological.


METHODS
We used a single fibre in vitro motility assay. The in vitro motility speed of actin filaments propelled by myosin extracted from fibres expressing type I myosin heavy chain (MyHC; n = 9), IIa MyHC (n = 6), IIax MyHC (n = 4) and I/IIa MyHC (n = 1) was measured at 15, 20, 25, 30 and 35 degrees C.


RESULTS
The motility speed between groups of fibres expressing different MyHC differed significantly (P << 0.001). The increase in motility speed with an increase in temperature was statistically significant (P << 0.001) between all temperatures. The relative difference in motility speed between the slow type I and the fast IIax MyHC fibres decreased with increasing temperature, i.e. a 7.5-fold difference at 15 degrees C was reduced to twofold at 35 degrees C. Furthermore, the twofold difference in motility speed between type IIa and IIax MyHC at 15 degrees C disappeared completely at 35 degrees C. The activation energy, E(A), and temperature coefficient, Q(10), over the 15-35 degrees C temperature range was higher for type I MyHC, 54.47 +/- 4.37 kJ mol(-1) and 2.09 +/- 0.12, respectively, than for type IIa MyHC, 45.41 +/- 3.12 kJ mol(-1) (P < 0.001) and 1.85 +/- 0.08 (P < 0.001), or IIax MyHC, 34.71 +/- 1.75 kJ mol(-1) (P << 0.001) and 1.60 +/- 0.04 (P << 0.001).


CONCLUSIONS
The present results suggest a significantly reduced difference in shortening velocity between different human muscle fibre types at physiological temperature than previously reported at lower temperatures (12 or 15 degrees C) with implications for human in vivo muscle function.
Department of Clinical Neurophysiology, Uppsala University, Uppsala, SE, Sweden. AUL104@psu.edu
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Lionikas
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Larsson
D008841:Actin Cytoskeleton / Q000502:physiology; D000328:Adult; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D020033:Protein Isoforms / Q000502:physiology; D011817:Rabbits; D024744:Skeletal Muscle Myosins / Q000502:physiology*; D013696:Temperature
D020033:Protein Isoforms; D024744:Skeletal Muscle Myosins