The thermogenic function of the sarcoplasmic reticulum Ca2+-ATPase of normal and hyperthyroid rabbit.
After formation of a Ca(2+) gradient, the amount of heat released during the hydrolysis of each mol of ATP cleaved (DeltaH(cal)) varies depending on the Ca(2+)-ATPase isoform expressed by the muscle cell. In vesicles derived from the sarcoplasmic reticulum of white muscle (SERCA 1) most of the ATP cleaved is not coupled to Ca(2+) transport, and the DeltaH(cal) varies between -20 and -22 kcal/mol. In contrast, in vesicles derived from red muscle (SERCA 2a) the hydrolysis of ATP is coupled with Ca(2+) transport, and the DeltaH(cal) varies between -12 and -14 kcal/mol. Hyperthyroidism increases the rate of heat production by the Ca(2+)-ATPase fourfold in white muscle and 40-fold in red muscle. In hyperthyroid rabbits, the amount of sarcoplasmic reticulum protein recovered from white and red muscle is four- to fivefold greater than that obtained from control rabbits. Hyperthyroid red muscle expresses SERCA 1, and the vesicles derived from these muscle hydrolyze ATP through a catalytic route that is not coupled to Ca(2+) transport, thus increasing the amount of heat released during ATP hydrolysis, the DeltaH(cal) varying between -20 and -22 kcal/mol.
de Meis
Leopoldo
L
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, Brasil. demeis@bioqmed.ufrj.br
Arruda
Ana Paula
AP
da-Silva
Wagner S
WS
Reis
Marcelo
M
Carvalho
Denise P
DP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D006980:Hyperthyroidism / Q000201:enzymology / Q000503:physiopathology*; D007700:Kinetics; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000502:physiology; D011817:Rabbits; D012016:Reference Values; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D014158:Transcription, Genetic
D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases