dual component analysis explains the distinctive kinetics of cAMP accumulation in brown adipocytes

• Published in: The Journal of biological chemistry 1999-12, Vol.274 (53), p.37770-37780
• Main Authors: Bronnikov, G.E, Zhang, S.J, Cannon, B, Nedergaard, J
• Format: Article
• Language: English
• Subjects: adipocytes; Adipocytes - drug effects; Adipocytes - enzymology; Adipocytes - metabolism; Adipose Tissue, Brown - drug effects; Adipose Tissue, Brown - enzymology; Adipose Tissue, Brown - metabolism; Adrenergic beta-Agonists - pharmacology; agonists; Animals; biosynthesis; brown adipose tissue; calcium; Calcium - metabolism; Calmodulin - metabolism; cyclic AMP; Cyclic AMP - metabolism; cytochemistry; dose response; Dose-Response Relationship, Drug; Enzyme Activation; enzyme activity; enzyme inhibitors; inorganic ions; isoprenaline; Isoproterenol - pharmacology; Kinetics; Male; Medicin och hälsovetenskap; metabolic inhibitors; Mice; norepinephrine; Norepinephrine - pharmacology; phosphodiesterase I; Phosphodiesterase Inhibitors - pharmacology; Phosphoric Diester Hydrolases - metabolism; Protein Kinase C - metabolism; rats; Receptors, Adrenergic, beta - drug effects; Receptors, Adrenergic, beta-3
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.53.37770

The mechanism behind the distinctive non-Michaelis-Menten, bell-shaped kinetics of cAMP accumulation in brown adipocytes (which underlies the similar kinetics of UCP1 and β 1 -adrenoreceptor gene expression) was investigated. A theoretical dual component analysis indicated that the observed dose-response curves could be constructed as the resultant of a stimulatory and an inhibitory component. Experimentally, inhibition of the α 1 -component of the norepinephrine response revealed the underlying existence of a much larger stimulatory β 3 -component which displayed monophasic Michaelis-Menten kinetics. The inhibitory α 1 -component (which was also monophasic but had a 2-fold higher EC 50 ) was mediated via an increase in [Ca 2+ ] i ; the protein kinase C pathway was not involved. The [Ca 2+ ] i increase which resulted in massive inhibition of cAMP accumulation was very low: