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Caveolae compartmentalise ?2-adrenoceptor signals by curtailing cAMP production and maintaining phosphatase activity in the sarcoplasmic reticulum of the adult ventricular myocyte.

ABSTRACT: Inotropy and lusitropy in the ventricular myocyte can be efficiently induced by activation of ?1-, but not ?2-, adrenoceptors (ARs). Compartmentation of ?2-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 ?2-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-?-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 ?2-AR stimulation, consistent with MBCD acting via caveolae. Biosensor experiments revealed ?2-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 ?2-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 ?2-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".

SUBMITTER: Macdougall DA

PROVIDER: S-EPMC3270222 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Caveolae compartmentalise β2-adrenoceptor signals by curtailing cAMP production and maintaining phosphatase activity in the sarcoplasmic reticulum of the adult ventricular myocyte.

Macdougall David A DA Agarwal Shailesh R SR Stopford Elizabeth A EA Chu Hongjin H Collins Jennifer A JA Longster Anna L AL Colyer John J Harvey Robert D RD Calaghan Sarah S

Journal of molecular and cellular cardiology 20110626 2

Inotropy and lusitropy in the ventricular myocyte can be efficiently induced by activation of β1-, but not β2-, adrenoceptors (ARs). Compartmentation of β2-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 β2-ARs (with zinterol/CGP20712A) produced little ...[more]

PMID: 21740911

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Project description:Abnormal cellular Ca2+ handling contributes to both contractile dysfunction and arrhythmias in heart failure. Reduced Ca2+ transient amplitude due to decreased sarcoplasmic reticulum Ca2+ content is a common finding in heart failure models. However, heart failure models also show increased propensity for diastolic Ca2+ release events which occur when sarcoplasmic reticulum Ca2+ content exceeds a certain threshold level. Such Ca2+ release events can initiate arrhythmias. In this study we aimed to investigate if both of these aspects of altered Ca2+ homeostasis could be found in left ventricular cardiomyocytes from rats with different states of cardiac function six weeks after myocardial infarction when compared to sham-operated controls. Video edge-detection, whole-cell Ca2+ imaging and confocal line-scan imaging were used to investigate cardiomyocyte contractile properties, Ca2+ transients and Ca2+ waves. In baseline conditions, i.e. without beta-adrenoceptor stimulation, cardiomyocytes from rats with large myocardial infarction, but without heart failure, did not differ from sham-operated animals in any of these aspects of cellular function. However, when exposed to beta-adrenoceptor stimulation, cardiomyocytes from both non-failing and failing rat hearts showed decreased sarcoplasmic reticulum Ca2+ content, decreased Ca2+ transient amplitude, and increased frequency of Ca2+ waves. These results are in line with a decreased threshold for diastolic Ca2+ release established by other studies. In the present study, factors that might contribute to a lower threshold for diastolic Ca2+ release were increased THR286 phosphorylation of Ca2+/calmodulin-dependent protein kinase II and increased protein phosphatase 1 abundance. In conclusion, this study demonstrates both decreased sarcoplasmic reticulum Ca2+ content and increased propensity for diastolic Ca2+ release events in ventricular cardiomyocytes from rats with heart failure after myocardial infarction, and that these phenomena are also found in rats with large myocardial infarctions without heart failure development. Importantly, beta-adrenoceptor stimulation is necessary to reveal these perturbations in Ca2+ handling after a myocardial infarction.

Dataset Information

Caveolae compartmentalise ?2-adrenoceptor signals by curtailing cAMP production and maintaining phosphatase activity in the sarcoplasmic reticulum of the adult ventricular myocyte.

Publications

Caveolae compartmentalise β2-adrenoceptor signals by curtailing cAMP production and maintaining phosphatase activity in the sarcoplasmic reticulum of the adult ventricular myocyte.

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