PubMed · 12529280
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Gerald F DiBona. 2003. Thermoregulation.. https://doi.org/10.1152/ajpregu.00571.2002
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Atp11p (Atpaf1p; F(1)-ATPase assembly factor 1) and Atp12p (Atpaf2p; F(1)-ATPase assembly factor 2) are proteins required for the assembly of beta (F(1)-beta) and alpha (F(1)-alpha) subunits into the mitochondrial ATPase. Here we report about 100 times lower levels of ATPAF1 and ATPAF2 transcripts in relation to the mRNA levels of F(1)-alpha and F(1)-beta in a range of mouse tissues. Quantitative reverse-transcription polymerase chain reaction revealed nearly constant ATPAF1 expression in all tissues in both adult and 5-day-old mice (up to two-fold differences), indicating that ATPAF1 rather behaves like a maintenance gene. In contrast, ATPAF2 expression differed up to 30-fold in the tissues analysed. ATPAF2 tissue-specific expression was also found to correlate well with mRNA levels of both F(1)-alpha and F(1)-beta (BATz.Gt;kidney, liver>heart, brain>skeletal muscle), showing the highest mRNA level in the thermogenic, ATPase-poor brown adipose tissue, which is characterised by a 10-fold decrease in ATPase/respiratory chain stoichiometry relative to the other tissues.
Chemical sympathectomy with guanethidine (Gnt) selectively destroys the postganglionic noradrenergic neurons, whereas dopaminergic fibers and nonneural catecholamine-secreting cells are spared. As a result, the relative proportions of norepinephrine (NE), epinephrine (E), and dopamine (DA) in tissues can be differentially affected. This study was done to show the possible differences in the relative amount of catecholamines in some organs and tissues that might indicate the nature of the secretory cells from which they originate. The contents of NE, E, and DA were assessed in rats neonatally treated with Gnt. Gnt-treated rats showed significantly lower levels of NE (P < 0.01) in all tissues except the adrenal gland and paraganglia. Epinephrine was present in all tissues with mean levels below 25 ng/g, with the exception of the adrenal gland (700 microg/gland) and paraganglia (100 ng/g). Only the heart showed lower values in Gnt-treated rats. Mean DA levels were also very high in paraganglia (530 ng/g). In the Gnt-treated rats, DA levels fell practically to zero except in the duodenum, mesentery, and adrenal, whereas there were high levels in the paraganglia, which were significantly different from controls. The results suggest that the three catecholamines are contained mainly in noradrenergic sympathetic fibers of muscle, white adipose tissue, heart, liver, pancreas, and spleen. The duodenum and mesentery may have dopaminergic fibers or E- and DA-containing nonneural cells. Hepatic-vagus paraganglia contain all the catecholamines in relatively high amounts in nonneural cells, and Gnt treatment raises DA levels without affecting the other amines.
In this report a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) was identified in rats brown adipose tissue. Electrophoretic analysis of brown fat microssomal protein yields a 110-kDa band that is reactive to SERCA 1 antibody but is not reactive to SERCA 2 antibodies. Nevertheless, the kinetics properties of the brown fat SERCA differ from the skeletal muscle SERCA 1 inasmuch they manifest a different Ca2+ affinity and a much higher degree of ATPase/Ca2+ uncoupling. A SERCA enzyme is not found in white fat. Fatty acids promoted Ca2+ leakage from brown fat vesicles. The heat released during ATP hydrolysis was -24.7 kcal/mol when a Ca2+ gradient was formed across the vesicles membrane and -14.4 kcal/mol in the absence of a gradient. The data reported suggest that in addition to storing Ca2+ inside the endoplasmic reticulum, the Ca2+-ATPase may represent a source of heat production contributing to the thermogenic function of brown adipose tissue.