Norepinephrine induces slow calcium signalling in murine brown preadipocytes through the beta-adrenoceptor/cAMP/protein kinase A pathway.
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 ( approximately 10 nM/min) without a burst and a maximum, whereas in mature brown adipocytes, the quick burst reached 1.5 microM [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 beta-selective antagonist nadolol almost completely prevented the effect of NE on [Ca(2+)](i), while the antagonist of alpha-adrenoceptors phentolamine caused only a approximately 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 beta-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 alpha(1)-adrenoceptors and the trigger mechanism.
Dolgacheva
Ludmila P
LP
Institute of Cell Biophysics, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia.
Abzhalelov
Bakhytbek B
BB
Zhang
Shi-Jin
SJ
Zinchenko
Valery P
VP
Bronnikov
Gennady E
GE
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000166:cytology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009638:Norepinephrine / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015363:Quinolones / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D013449:Sulfonamides; D019284:Thapsigargin / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D010726:Phosphodiesterase Inhibitors; D015363:Quinolones; D011943:Receptors, Adrenergic, beta; D013449:Sulfonamides; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D019284:Thapsigargin; C060853:OPC 3911; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D015056:1-Methyl-3-isobutylxanthine; D009638:Norepinephrine