Meeting Abstract
Factors that limit thermal tolerance in stenothermal Antarctic notothenioids are not fully understood. In this study, properties of neuronal membranes of red-blooded Notothenia coriiceps and the hemoglobin-lacking icefish Chaenocephalus aceratus were analyzed. Myelin, synaptosomes, and mitochondria were fractionated from brain tissue using a Percoll gradient. Membrane fluidities between 0 and 40°C were quantified by fluorescence depolarization. Cholesterol levels were measured in synaptosomes and myelin, and polar lipid compositions were analyzed in myelin. Synaptosomes from N. coriiceps showed consistently higher membrane order than C. aceratus (P<0.0001), yet synaptosomal cholesterol-to-phospholipid ratios were similar among species. Although fluidity of myelin and mitochondria did not differ significantly between species over the measured temperature range, the thermal sensitivity of fluidity in both membranes was lower in C. aceratus than N. coriiceps. In myelin, cholesterol-to-phospholipid ratios were approximately 2-fold greater in C. aceratus than N. coriiceps (P<0.05). Ratios of the two major phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), differed significantly in myelin between species, with N. coriiceps displaying a higher PC:PE ratio (P<0.001). Although cholesterol levels do not account for differences in synaptosomal fluidity, cholesterol is likely to influence the thermal dependence of fluidity in myelin. Myelin enriched in lipids with known fluidizing properties appears more susceptible to fluidization with warming. Additionally, the greater perturbation in membrane fluidity with elevations in temperature in N. coriiceps may contribute to species differences in behavior with acute warming (see Ismailov et al., this meeting). Supported by NSF ANT 1341602.
