Contractile and Metabolic Characteristics of Muscle Fibres From Antarctic Fish

Abstract

Contractile properties were determined for muscles from three species of Antarctic fish with broadly similar activity patterns: Trematomus hansoni, Notothenia rossii and Chaenocephalus aceratus. C. aceratus differs from the other species in that the genes for the respiratory pigments are not expressed.Red and white fibres were isolated from the pectoral fin adductor and trunk muscles, respectively. Fibre segments were chemically skinned with the nonionic detergent Brij-58. All experiments were carried out at 0°C. Maximum isometric tensions (P0) were 6·6–7·1 Ncm−2 for red, and 21·4–25·1 N cm−2 for white muscle fibres. The force-velocity (P-V) characteristics of muscle fibres were determined by step isotonic releases. Unloaded contraction velocities (muscle lengthss−1, L0S−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 (A. rossii) and 22·7 (C. aceratus). Corresponding values for red pectoral muscle fibres were around 4·2Wkg−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 aerobic mitochondrial metabolism (cytochrome oxidase) were measured in muscle homogenates from C. aceratus and N. rossii at 0°C. Red pectoral muscle fibres from C. aceratus and N. rossii had similar activities of cytochrome oxidase, carnitine palmitoyltransferase and glycolytic enzymes. Hexokinase activities 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 mechanical characteristics of the swimming muscles in C. aceratus apppear to be similar to those of other Notothenioids. Power outputs and enzyme activities of Antarctic fish muscle measured at 0 °C are comparable to those for temperate species measured at 15 or 25 °C, indicating a high degree of cold-adaptation of both energy-producing and energy-utilizing pathways.