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

Abstract

ABSTRACT Flounder (Platichthys flesus L.) were acclimated in sea water for 1-2 months to either 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-test method. 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 kN m−2 at 0°C to 200 kN m−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 relationship with 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 glucose utilization (hexokinase) and fatty acid oxidation (carnitine palmitoyl transferase) are 1·5–2·8 times higher in muscles of cold-acclimated compared to warm-acclimated flounders. Increases in the activities of these enzymes with cold acclimation may serve to offset the effects of low temperature on aerobic ATP supply. Glycolytic enzyme activities (phosphofructokinase, lactate dehydrogenase), however, are similar 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.