title: Fusion of the endoplasmic reticulum and mitochondrial outer membrane in rats brown adipose tissue: activation of thermogenesis by Ca2+.
abstract: Brown adipose tissue (BAT) mitochondria thermogenesis is regulated by uncoupling protein 1 (UCP 1), GDP and fatty acids. In this report, we observed fusion of the endoplasmic reticulum (ER) membrane with the mitochondrial outer membrane of rats BAT. Ca(2+)-ATPase (SERCA 1) was identified by immunoelectron microscopy in both ER and mitochondria. This finding led us to test the Ca(2+) effect in BAT mitochondria thermogenesis. We found that Ca(2+) increased the rate of respiration and heat production measured with a microcalorimeter both in coupled and uncoupled mitochondria, but had no effect on the rate of ATP synthesis. The Ca(2+) concentration needed for half-maximal activation varied between 0.08 and 0.11 microM. The activation of respiration was less pronounced than that of heat production. Heat production and ATP synthesis were inhibited by rotenone and KCN. Liver mitochondria have no UCP1 and during respiration synthesize a large amount of ATP, produce little heat, GDP had no effect on mitochondria coupling, Ca(2+) strongly inhibited ATP synthesis and had little or no effect on the small amount of heat released. These finding indicate that Ca(2+) activation of thermogenesis may be a specific feature of BAT mitochondria not found in other mitochondria such as liver.
authors.affiliation: Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil. demeis@bioqmed.ufrj.br
authors.forename: Leopoldo
authors.initials: L
authors.lastname: de Meis
authors.forename: Luisa A
authors.initials: LA
authors.lastname: Ketzer
authors.forename: Rodrigo Madeiro
authors.initials: RM
authors.lastname: da Costa
authors.forename: Ivone Rosa
authors.initials: IR
authors.lastname: de Andrade
authors.forename: Marlene
authors.initials: M
authors.lastname: Benchimol
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000273:Adipose Tissue / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D002151:Calorimetry / Q000379:methods; D003485:Cyanates / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D012402:Rotenone / Q000494:pharmacology
chemical_list: D003485:Cyanates; D012402:Rotenone; D000255:Adenosine Triphosphate; C024835:potassium cyanate