Kinetic characteristics of hamster (Mesocricetus auratus) brown fat (Na+/K+)-ATPase: effects of catecholamines.
1. The (Na+/K+)-ATPase activity of brown fat membranes is increased by norepinephrine, the physiological mediator of thermogenesis in this tissue. 2. This increased ATPase activity was inhibited approximately 50% by either propranolol (a beta-adrenergic blocker) or phentolamine (an alpha-blocker). 3. The alpha-agonist, phenylephrine and the beta-agonist, isoproterenol, also stimulated the ATPase activity. 4. That these latter effects were receptor-specific is supported by the finding that: (a) l(-)isoproterenol stimulation was inhibited by propranolol but not by phentolamine; (b) d(+)isoproterenol had no stimulatory effect on the ATPase activity; and (c) the l(-)phenylephrine-induced increase was inhibited by phentolamine but not by propranolol. 5. (-)norepinephrine, l(-)isoproterenol and l(-)phenylephrine all decreased the apparent Km for K+ of the (Na+/K+)-ATPase but did not alter the apparent Km for ATP or the Vmax of the reaction.
D002001:Adipose Tissue, Brown / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D006224:Cricetinae; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008647:Mesocricetus; D009638:Norepinephrine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D010656:Phenylephrine; D011433:Propranolol; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D009638:Norepinephrine; D010646:Phentolamine