AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 1 1-R7, Copyright © 1987 by American Physiological Society

ARTICLES

Evolution of mammalian endothermic metabolism: "leaky" membranes as a source of heat

P. L. Else and A. J. Hulbert

O2 consumption was measured at 37 degrees C in tissue slices of liver, kidney, and brain from Amphibolurus vitticeps and Rattus norvegicus (a reptile and mammal with same weight and body temperature) both in the presence and absence of ouabain. O2 consumption of the mammalian tissues was two to four times that of the reptilian tissues and the mammalian tissues used three to six times the energy for Na+-K+ transport than the reptilian tissues. Passive permeability to 42K+ was measured at 37 degrees C in liver and kidney slices, and passive permeability to 22Na+ was measured at 37 degrees C in isolated and cultured liver cells from each species. The mammalian cell membrane was severalfold "leakier" to both these ions than was the reptilian cell membrane, and thus the membrane pumps must use more energy to maintain the transmembrane ion gradients. It is postulated that this is a general difference between the cells of ectotherms and endotherms and thus partly explains the much higher levels of metabolism found in endothermic mammals.

This article has been cited by other articles:

				A. B. Salmon, A. A. S. Akha, R. Buffenstein, and R. A. Miller Fibroblasts From Naked Mole-Rats Are Resistant to Multiple Forms of Cell Injury, But Sensitive to Peroxide, Ultraviolet Light, and Endoplasmic Reticulum Stress J. Gerontol. A Biol. Sci. Med. Sci., March 1, 2008; 63(3): 232 - 241. [Abstract] [Full Text] [PDF]

				K. E. Conley, C. E. Amara, S. A. Jubrias, and D. J. Marcinek Muscle-energetic and cardio-pulmonary determinants of exercise tolerance in humans: Mitochondrial function, fibre types and ageing: new insights from human muscle in vivo Exp Physiol, March 1, 2007; 92(2): 333 - 339. [Abstract] [Full Text] [PDF]

				N. Turner, K. L. Haga, A. J. Hulbert, and P. L. Else Relationship between body size, Na+-K+-ATPase activity, and membrane lipid composition in mammal and bird kidney Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2005; 288(1): R301 - R310. [Abstract] [Full Text] [PDF]

				B. J. Wu, A. J. Hulbert, L. H. Storlien, and P. L. Else Membrane lipids and sodium pumps of cattle and crocodiles: an experimental test of the membrane pacemaker theory of metabolism Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2004; 287(3): R633 - R641. [Abstract] [Full Text] [PDF]

				D. Padron, M. E. Bizeau, and J. R. Hazel Is fluid-phase endocytosis conserved in hepatocytes of species acclimated and adapted to different temperatures? Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2000; 278(2): R529 - R536. [Abstract] [Full Text] [PDF]

				P. G. Wood, O. V. Lopatko, S. Orgeig, J. R. Codd, and C. B. Daniels Control of pulmonary surfactant secretion from type II pneumocytes isolated from the lizard Pogona vitticeps Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1999; 277(6): R1705 - R1711. [Abstract] [Full Text] [PDF]

				M. Fickova, P. Hubert, G. Crémel, and C. Leray Dietary (n-3) and (n-6) Polyunsaturated Fatty Acids Rapidly Modify Fatty Acid Composition and Insulin Effects in Rat Adipocytes J. Nutr., March 1, 1998; 128(3): 512 - 519. [Abstract] [Full Text]

				W. Lockette, K. Kirkland, and S. Farrow {alpha}2-Adrenergic Agonists Increase Cellular Lactate Efflux Hypertension, May 1, 1996; 27(5): 1104 - 1107. [Abstract] [Full Text]