Contractile and metabolic characteristics of muscle fibres from Antarctic fish
Contractile properties were determined for muscles from three species ofAntarctic fish with broadly similar activity patterns:Trematomus hansoni, Notothenia rossii and Chaenocephalus aceratus. C. aceratus differs from theother species in that the genes for the respiratory pigments are not expressed. Red and white fibres were isolated from the pectoral fin adductor and trunkmuscles, respectively. Fibre segments were chemically skinned with the nonionicdetergent Brij-58. All experiments were carried out at 0°C. Maximum isometric tensions (Po) were 6.6–7.1 Ncm−2for red, and 21.4–25.1 Ncm−2 for white muscle fibres. The force-velocity (P-V) characteristics of musclefibres were determined by step isotonic releases. Unloaded contraction velocities (muscle lengths s−1, Los−1) were 0.7 for red, and 0.9?-1.1 for white fibres. Maximum mechanical power outputs (Wkg−1 muscle for white muscle), calculated using Hill's equation for muscle shortening, were 26.7 (T.hansoni), 15.7 (N. rossii) and 22.7 (C. aceratus). Corresponding values forred pectoral muscle fibres were around 4.2 Wkg−1 for all three species. Maximum activities of enzymes of carbohydrate utilization (hexokinase, phosphofructokinase, lactate dehydrogenase), fatty acid metabolism (carnitine palmitoyl transferase, 3-OH acyl CoA dehydrogenase) and aerobicmitochondrial metabolism (cytochrome oxidase) were measured in musclehomogenates from C. aceratus and N. rossii at 0°C. Red pectoral musclefibres from C. aceratus and N. rossii had similar activities of cytochromeoxidase, carnitine palmitoyltransferase and glycolytic enzymes. Hexokinaseactivities were two times higher in the red fibres of C. aceratus than N. rossii, suggesting a greater capacity for aerobic glucose utilization in the former species. In spite of the lack of respiratory pigments, the metabolic and mechanicalcharacteristics of the swimming muscles in C. aceratus apppear to be similarto those of other Notothenioids. Power outputs and enzyme activities ofAntarctic fish muscle measured at 0°C are comparable to those for temperatespecies measured at 15 or 25°C, indicating a high degree of cold-adaptation ofboth energy-producing and energy-utilizing pathways.