Does the membrane pacemaker theory of metabolism explain the size dependence of metabolic rate in marine mussels?
According to the membrane pacemaker theory of metabolism (MPT), allometric scaling of metabolic rate in animals is determined by the composition of cellular and mitochondrial membranes, which changes with body size in a predictable manner. MPT has been elaborated from interspecific comparisons in mammals. It projects that the degree of unsaturation of membrane phospholipids decreases in larger organisms, thereby lowering ion permeability of the membranes and making cellular, and thus whole-animal metabolism more efficient. Here, we tested the applicability of the MPT to a marine ectotherm, the musselMytilus edulisat the intraspecific level. We determined effects of body mass on whole-organism, tissue and cellular oxygen consumption rates, on heart rate, metabolic enzyme activities and on the lipid composition of membranes. In line with allometric patterns, the organismal functions and processes such as heart rate, whole-animal respiration rate and phospholipid contents showed a mass-dependent decline. However, the allometry of tissue and cellular respiration and activity of metabolic enzymes was poor; fatty acid unsaturation of membrane phospholipids of gill tissue was independent of animal size. It is thus conceivable that most of the metabolic allometry observed at the organismal level is determined by systemic functions. These whole-organism patterns may be supported by energy savings associated with growing cell size but not by structural changes in membranes. Overall, the set of processes contributing to metabolic allometry in ectotherms may differ from that operative in mammals and birds, with a reduced involvement of the mechanisms proposed by the MPT.
White Sea Biological Station, Zoological Institute of Russian Academy of Sciences, Saint-Petersburg 199034, Russia Alexey.Sukhotin@zin.ru.|Department of Invertebrate Biology, Saint-Petersburg State University, Saint-Petersburg 199034, Russia.
Alexey
0000-0003-2626-5317
A
Sukhotin
Laboratory for Environmental Biochemistry, Institute of Biology, Karelian Research Centre of Russian Academy of Sciences, Petrozavodsk 185910, Russia.
Natalia
N
Fokina
Laboratory for Environmental Biochemistry, Institute of Biology, Karelian Research Centre of Russian Academy of Sciences, Petrozavodsk 185910, Russia.
Tatiana
T
Ruokolainen
Integrative Ecophysiology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven D-27570, Germany.
Christian
C
Bock
Integrative Ecophysiology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven D-27570, Germany.|University of Bremen, Bremen 28359, Germany.
Hans-Otto
HO
Pörtner
Integrative Ecophysiology, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven D-27570, Germany.
Gisela
G
Lannig
D000818:Animals; D001481:Basal Metabolism; D049628:Body Size; D002478:Cells, Cultured; D005227:Fatty Acids / Q000378:metabolism; D005880:Gills / Q000033:anatomy & histology / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D006339:Heart Rate; D049880:Mytilus edulis / Q000033:anatomy & histology / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D010101:Oxygen Consumption; D010743:Phospholipids / Q000378:metabolism
D005227:Fatty Acids; D010743:Phospholipids
Allometric scaling; Cardiac magnetic resonance imaging; Cells; Enzyme activity; Fatty acids; Heart rate