title: Identification of a Ca2+-ATPase in brown adipose tissue mitochondria: regulation of thermogenesis by ATP and Ca2+.
abstract: In brown adipose tissue (BAT) adrenaline promotes a rise of the cytosolic Ca(2+) concentration from 0.05 up to 0.70 mum. It is not known how the rise of Ca(2+) concentration activates BAT thermogenesis. In this report we compared the effects of Ca(2+) in BAT and liver mitochondria. Using electron microscopy and immunolabeling we identified a sarco/endoplasmic reticulum (ER) Ca(2+)-ATPase bound to the inner membrane of BAT mitochondria. A Ca(2+)-dependent ATPase activity was detected in BAT mitochondria when the respiratory substrates malate and pyruvate were included in the medium. ATP and Ca(2+) enhanced the amount of heat produced by BAT mitochondria during respiration. The Ca(2+) concentration needed for half-maximal activation of the ATPase activity and rate of heat production were the same and varied between 0.1 and 0.2 mum. Heat production was partially inhibited by the proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone and abolished by thapsigargin, a specific ER Ca(2+)-ATPase inhibitor, and by both rotenone and KCN, two substances that inhibit the electron transfer trough the mitochondrial cytochrome chain. In liver mitochondria Ca(2+) did not stimulate the ATPase activity nor increase the rate of heat production. Thapsigargin had no effect on liver mitochondria. In conclusion, this is the first report of a Ca(2+)-ATPase in mitochondria that is BAT-specific and can generate heat in the presence of Ca(2+) concentrations similar to those noted in the cell during adrenergic stimulation.
authors.affiliation: Instituto de Bioquímica Médica, Prédio CCS, Universidade Federal do Rio de Janeiro, Cidade Universitária, RJ 21941-590, Brazil. demeis@bioqmed.ufrj.br
authors.forename: Leopoldo
authors.initials: L
authors.lastname: de Meis
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Arruda
authors.forename: Rodrigo Madeiro
authors.initials: RM
authors.lastname: da Costa
authors.forename: Marlene
authors.initials: M
authors.lastname: Benchimol
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000201:enzymology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008564:Membrane Potentials; D008854:Microscopy, Electron / Q000379:methods*; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
chemical_list: D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D000252:Calcium-Transporting ATPases; D002118:Calcium