205 Original Paper Cell Physiol Biochem 2007;19:205-212 Accepted: October 16, 2006 Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology and Biochemistr and Biochemistr and Biochemistr and Biochemistr and Biochemistry Copyright © 2007 S. Karger AG, Basel Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com © 2007 S. Karger AG, Basel 1015-8987/07/0194-0205$23.50/0 Accessible online at: www.karger.com/journals/net Skeletal Muscle of Female Rats Exhibit Higher Mitochondrial Mass and Oxidative- Phosphorylative Capacities Compared to Males Bartomeu Colom, Maria Pilar Alcolea, Adamo Valle, Jordi Oliver, Pilar Roca and Francisco J. García-Palmer Grup de Metabolisme Energètic i Nutrició. Departament de Biología Fonamental i Ciències de la Salut. Institut Universitari d´Investigació en Ciències de la Salut (IUNICS). Universitat de les Illes Balears, E-07122 Palma de Mallorca, Spain Dr. FJ García-Palmer Dept. Biologia Fonamental i Ciències de la Salut Universitat de les Illes Balears Ctra. Valldemossa km 7.5. E-07122 Palma de Mallorca (Spain) Tel. +34 971 173173, Fax +34 971 173 184, E-Mail paco.garcia-palmer@uib.es Key Words Mitochondria  Gender dimorphism  Skeletal muscle  Oxidative metabolism  Mitochondrial biogenesis Abstract The effect of gender and caloric restriction on mitochondrial content and oxidative-phosphorylative capacities has been investigated in rat gastrocnemius muscle. Muscle protein, mitochondrial protein and DNA contents, enzymatic activities of mitochondrial oxidative and phosphorylative system, mitochondrial antioxidant enzymes, protein levels of complex IV (subunit I and IV) and ATPase, and the gene and protein expression of mitochondrial transcription factor A (TFAM), involved in mitochondrial replication and transcription, were measured in rats of both genders fed ad libitum and subjected to three months of 40% caloric restriction. Compared to males, gastrocnemius muscle of female rats showed higher mitochondrial DNA and protein contents, TFAM protein level, oxidative and phosphorylative machinery and activities, and glutathione peroxidase activity. In conclusion, the present data show a clear gender dimorphism in rat muscle mitochondrial features, which could explain the higher facility of females to adapt to altered metabolic energy situations. Introduction Several studies have reported a gender dimorphism in energy balance in basal conditions, with a higher total energy expenditure in female compared to male rats [1, 2]. However, when animals are subjected to situations where an extra energy demand is necessary, females are able to respond positively to a greater extent than males [3, 4]. One of these situations is the adaptation to caloric restriction periods, where female rats decrease their energy expenditure while preserving metabolically active organ mass [2, 5]. Caloric restriction is a normal situation in nature and, during evolution, females may have developed better mechanisms than males to face these food deprivation periods and survive, probably because they are subjected to more severe selection pressures during lack of food supply [6]. The gender differences in energy efficiency can be linked to changes in the mechanisms to obtain this energy,