Norepinephrine induces slow calcium signalling in murine brown preadipocytes through the β-adrenoceptor/cAMP/protein kinase A pathway

• Published in: Cellular signalling 2003-02, Vol.15 (2), p.209-216
• Main Authors: Dolgacheva, Ludmila P, Abzhalelov, Bakhytbek B, Zhang, Shi-Jin, Zinchenko, Valery P, Bronnikov, Gennady E
• Format: Article
• Language: English
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; 4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone - pharmacology; Adipocytes - drug effects; Adipocytes - metabolism; Adipose Tissue, Brown - cytology; Adrenergic alpha-Agonists - pharmacology; Adrenergic beta-Agonists - pharmacology; Animals; Brown adipocytes; Calcium Signaling - drug effects; Calcium signalling; cAMP and Ca 2+ (norepinephrine, brown adipose tissue); Cell precursors; Cyclic AMP - metabolism; Cyclic AMP-Dependent Protein Kinases - metabolism; Enzyme Inhibitors - pharmacology; Isoproterenol - pharmacology; Isoquinolines - pharmacology; Male; Medicin och hälsovetenskap; Mice; Mice, Inbred Strains; Norepinephrine - pharmacology; Phosphodiesterase Inhibitors - pharmacology; Quinolones - pharmacology; Receptors, Adrenergic, beta - metabolism; Sulfonamides; Thapsigargin - pharmacology; β-adrenoceptors
• ISSN: 0898-6568; 1873-3913
• DOI: 10.1016/S0898-6568(02)00060-8

The mechanism of adrenergically activated calcium signalling in isolated murine brown preadipocytes (stromal–vascular fraction) was studied with Fura-2. Norepinephrine (NE) generated in preadipocytes a slow Ca 2+-response (∼10 nM/min) without a burst and a maximum, whereas in mature brown adipocytes, the quick burst reached 1.5 μM [Ca 2+] i. Thapsigargin, which is known to discharge Ca 2+ ions from the IP 3-sensitive stores, initiated a huge capacitative calcium entry in mature brown adipocytes but failed to stimulate a response in preadipocytes. The β-selective antagonist nadolol almost completely prevented the effect of NE on [Ca 2+] i, while the antagonist of α-adrenoceptors phentolamine caused only a ∼25% reduction of the cellular response. Forskolin or the cell-permeable Br-cAMP caused [Ca 2+] i rise, which were even higher than with NE. The protein kinase A (PKA) inhibitor N-[2-( p-bromocynnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89) reduced and the phosphodiesterase inhibitors 3-isobutyl-1-methylxanthine (IBMX), N-cyclohexyl- N-(2-hydroxyethyl)-4-(6-(1,2-dihydro-2-oxoquinolyloxy))butyramide (OPC-3911), 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidone (Ro 20-1724) or the protein phosphatase inhibitor okadaic acid enhanced the NE-, isoproterenol- or forskolin-initiated cellular calcium responses. It was concluded that (i) brown preadipocytes lacked a trigger mechanism of initiation of [Ca 2+] i rises and (ii) the cAMP- and protein kinase A-mediated phosphorylation played an important role in the β-adrenoceptor-initiated calcium signalling in these cells. All these features distinguish brown adipocyte precursors from differentiated brown adipocytes, where calcium signalling is initiated exclusively via α 1-adrenoceptors and the trigger mechanism.