Regulation of Na+ transport in brown adipose tissue.
In order to test the hypothesis that Na+, K+-ATPase (Na+,K+-dependent ATPase) is involved in the noradrenaline-mediated stimulation of respiration in brown adipose tissue, the effects of noradrenaline on Na+,K+-ATPase in isolated brown-fat-cell membrane vesicles, and on 22Na+ and K+ (86Rb+) fluxes across the membranes of intact isolated cells, were measured. The ouabain-sensitive fraction of the K+-dependent ATPase activity in the isolated membrane-vesicle preparation was small and was not affected by the presence of noradrenaline in the incubation media. The uptake of 86Rb+ into intact hormone-sensitive cells was inhibited by 80% by ouabain, but it was insensitive to the presence of noradrenaline. 22Na+ uptake and efflux measured in the intact cells were 8 times more rapid than the 86Rb+ fluxes and were unaffected by ouabain. This indicated the presence of a separate, more active, transport system for Na+ than the Na+,K+-ATPase. This is likely to be a Na+/Na+ exchange activity under normal aerobic conditions. However, under anaerobic conditions, or conditions simulating anaerobiosis (2 mM-NaCN), the unidirectional uptake of Na+ increased dramatically, while efflux was unaltered.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003486:Cyanides / Q000494:pharmacology; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D008647:Mesocricetus; D009638:Norepinephrine / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase
D027682:Cation Transport Proteins; D003486:Cyanides; D007461:Iodoacetates; D010042:Ouabain; D012964:Sodium; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D002118:Calcium; D019807:Iodoacetic Acid; D009638:Norepinephrine