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Chemical and Physical Properties of Gill Plasma Membranes Are Altered in Response to Thermal Acclimation in the Antarctic Notothenioid Fish Notothenia coriiceps

Antarctic notothenioid fishes are highly stenothermal as a result of living under relatively stable conditions for millions of years. In a warming climate, preservation of membrane structure and function at elevated body temperatures will be critical to the survival of these species. Many ectothermic organisms can respond to thermal variation by altering membrane compositions to preserve membrane structure (i.e., homeoviscous adaptation). It is largely unknown to what extent Antarctic notothenioids possess the capacity to remodel their biological membranes in response to thermal change. We studied effects of thermal acclimation on physical (fluidity, permeability, oxygen solubility) and biochemical (lipid composition) properties of plasma membranes from the gills of an Antarctic notothenioid, Notothenia coriiceps. Animals were acclimated to 0 and 5°C for a minimum of 6 weeks. Plasma membranes were prepared from the gill, and membrane fluidity was measured from 0 to 30°C. Cholesterol contents and phospholipid compositions were analyzed in membranes, and permeability to water was measured in gills at both 0 and 4°C. Oxygen partition coefficients were determined in membrane samples to assess oxygen solubility. Membrane fluidity was reduced in the 5°C‐acclimated group, compared with animals held at 0°C (P<0.0001) and exhibited perfect (100%) homeoviscous efficacy. Membranes from 5°C‐acclimated fish also contained 1.2‐fold greater cholesterol (P<0.01) and 1.1‐fold greater long‐chain fatty acids (i.e., fatty acids with at least 20 carbon molecules per chain) (P<0.05). Water permeability was reduced 1.5‐fold with 5°C acclimation (P<0.05), exhibiting near‐perfect (96%) homeostatic efficacy. In contrast, oxygen solubility of membrane lipids was unchanged. The biochemical alterations with acclimation are in accord with changes in both fluidity and permeability, suggesting lipid restructuring occurred to conserve membrane structure at elevated temperature. Taken together, these results provide evidence of homeoviscous adaptation, and conservation of permeability, with temperature acclimation in gill plasma membranes from an Antarctic notothenioid.