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J Mol Cell Cardiol ; 52(2): 388-400, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-21740911

RESUMO

Inotropy and lusitropy in the ventricular myocyte can be efficiently induced by activation of ß1-, but not ß2-, adrenoceptors (ARs). Compartmentation of ß2-AR-derived cAMP-dependent signalling underlies this functional discrepancy. Here we investigate the mechanism by which caveolae (specialised sarcolemmal invaginations rich in cholesterol and caveolin-3) contribute to compartmentation in the adult rat ventricular myocyte. Selective activation of ß2-ARs (with zinterol/CGP20712A) produced little contractile response in control cells but pronounced inotropic and lusitropic responses in cells treated with the cholesterol-depleting agent methyl-ß-cyclodextrin (MBCD). This was not linked to modulation of L-type Ca(2+) current, but instead to a discrete PKA-mediated phosphorylation of phospholamban at Ser(16). Application of a cell-permeable inhibitor of caveolin-3 scaffolding interactions mimicked the effect of MBCD on phosphorylated phospholamban (pPLB) during ß2-AR stimulation, consistent with MBCD acting via caveolae. Biosensor experiments revealed ß2-AR mobilisation of cAMP in PKA II signalling domains of intact cells only after MBCD treatment, providing a real-time demonstration of cAMP freed from caveolar constraint. Other proteins have roles in compartmentation, so the effects of phosphodiesterase (PDE), protein phosphatase (PP) and phosphoinositide-3-kinase (PI3K) inhibitors on pPLB and contraction were compared in control and MBCD treated cells. PP inhibition alone was conspicuous in showing robust de-compartmentation of ß2-AR-derived signalling in control cells and a comparatively diminutive effect after cholesterol depletion. Collating all evidence, we promote the novel concept that caveolae limit ß2-AR-cAMP signalling by providing a platform that not only attenuates production of cAMP but also prevents inhibitory modulation of PPs at the sarcoplasmic reticulum. This article is part of a Special Issue entitled "Local Signaling in Myocytes".


Assuntos
Cavéolas/metabolismo , AMP Cíclico/biossíntese , Miócitos Cardíacos/metabolismo , Monoéster Fosfórico Hidrolases/metabolismo , Receptores Adrenérgicos beta 2/metabolismo , Retículo Sarcoplasmático/enzimologia , Transdução de Sinais , Animais , Cálcio/metabolismo , Cavéolas/efeitos dos fármacos , Células Cultivadas , Cromonas/farmacologia , Ventrículos do Coração/efeitos dos fármacos , Ventrículos do Coração/metabolismo , Masculino , Morfolinas/farmacologia , Contração Miocárdica/efeitos dos fármacos , Miócitos Cardíacos/efeitos dos fármacos , Inibidores de Fosfoinositídeo-3 Quinase , Fosforilação/efeitos dos fármacos , Transporte Proteico , Ratos , Ratos Wistar , Retículo Sarcoplasmático/metabolismo , beta-Ciclodextrinas/farmacologia
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