title: The thermal dependence of Na+ flux in isolated liver cells from ectotherms and endotherms.
abstract: The thermal dependence (0-40°C) of Na(+) flux in isolated liver cells of three endotherms (mice, rat and rabbit) was compared with that of ectotherms in the form of a thermally tolerant amphibian (cane toad), a cold-water fish (rainbow trout) and a thermophilic reptile (lizard). Mammals were found to share similar high rates of Na(+) flux (3.0-3.7 nmol Na(+) mg(-1) protein min(-1)) at their normal body temperatures (36-39°C). These Na(+) flux rates were significantly greater (P<0.0004-0.0001) than those of the ectotherms, which shared similar low rates of Na(+) flux (0.7-1.3 nmol Na(+) mg(-1) protein min(-1)) at their very different normal acclimated body temperatures (15°C for trout, 25°C for toad and 37°C for the lizard species). Trout, which possess highly unsaturated membranes (similar to those of mammals), showed a Na(+) flux with high thermal sensitivity at low temperatures similar to that found in mammals at higher temperatures. The thermal sensitivity of toad Na(+) flux was significantly less (P<0.05-0.01) than that of rat and rabbit. Trout Na(+) flux did not increase with increasing temperature much above 20°C, whereas all other species measured increased their Na(+) flux with increasing temperature up to 40°C. In conclusion, at normal operating body temperatures, the rate of Na(+) flux is much lower in ectotherms.
authors.affiliation: School of Medicine (IHMRI), University of Wollongong, Wollongong, NSW 2522, Australia pelse@uow.edu.au.
authors.forename: Paul L
authors.identifier: 0000-0001-9368-3231
authors.initials: PL
authors.lastname: Else
mesh_terms: D000818:Animals; D002469:Cell Separation / Q000379:methods*; D005227:Fatty Acids / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism*; D015227:Lipid Peroxidation; D008099:Liver / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D051379:Mice; D017686:Oncorhynchus mykiss / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013696:Temperature
chemical_list: D005227:Fatty Acids; D008563:Membrane Lipids; D012964:Sodium
keywords: Hepatocytes; Lizard; Mouse; Rabbit; Rat; Sodium pump metabolism; Tissue metabolism; Toad; Trout