Effects Of Temperature And Thermal Acclimation On Contractile Properties And Metabolism Of Skeletal Muscle In The Flounder (Platichthys Flesus L.)

Flounder (Platichthys flesus L.) were acclimated in sea water for 1–2 months toeither 5°C or 23°C (12h light: 12h dark photoperiod). Single fast muscle fibres were isolated from anterior ventral myotomes and skinned with detergent (Brij 58). Fibres were maximally activated and force-velocity (P-V) characteristics determined by step tension releases using an isotonic lever. Unloaded shortening speed was independently determined using the slack-testmethod. The contractile properties of flounder skinned fibres are not altered by temperature acclimation. Maximum isometric tension development has a low thermal dependence, Q10 = 1.2, increasing from 145 kNm−2 at 0°C to 200kNm −2 at 25°C. The force-velocity relationship becomes progressively less curved with decreasing temperature (higher values of Hill's constant a/P0) such that the thermal dependence of contraction velocity is significantly less at loads for optimum power output (Q10 = 1.3) than at zero load (Q10 = 2.0). Values for a/P0 are 0.27 at 0°C, 0.12 at 10°C and 0.08 at 25°C. Reductions in the curvature of the P-V relationshipwith decreasing temperature may represent an important mechanism for stabilizing muscle power output at low temperatures. Longer term metabolic adjustments to temperature were studied by determining maximal enzyme activities in fast and slow muscles (at 15°C). Activities of marker enzymes for mitochondrial metabolism (cytochrome oxidase), aerobic glucoseutilization (hexokinase) and fatty acid oxidation (carnitine palmitoyl transferase) are1.5-2.8 times higher in muscles of cold-acclimated compared to warm-acclimatedflounders. Increases in the activities of these enzymes with cold acclimation mayserve to offset the effects of low temperature on aerobic ATP supply. Glycolyticenzyme activities (phosphofructokinase, lactate dehydrogenase), however, aresimilar at both acclimation temperatures. The results are briefly discussed in relation to the ecology of the flounder and evolutionary strategies of temperature adaptation in teleosts.