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Phosphodiesterase 4 and phosphatase 2A differentially regulate cAMP/protein kinase a signaling for cardiac myocyte contraction under stimulation of beta1 adrenergic receptor.

ABSTRACT: Activation of the beta adrenergic receptor (betaAR) induces a tightly controlled cAMP/protein kinase A (PKA) activity to ensure an agonist dose-dependent and saturable contraction response in animal heart. We have found that stimulation of beta(1)AR by isoproterenol induces maximal contraction responses at the dose of 1 microM in cardiac myocytes; however, cAMP accumulation continues to increase with higher agonist concentrations. Dose-dependent cAMP accumulation is tightly controlled by negative regulator phosphodiesterase 4 (PDE4) that hydrolyzes cAMP. At 1 nM isoproterenol, cAMP accumulation is minimal because of the hydrolysis of cAMP by PDE4, which leads to a small increase in PKA phosphorylation of phospholamban and troponin I (TnI), and contraction responses. Inhibition of PDE4 activity with rolipram enhances cAMP accumulation, yields maximal PKA phosphorylation of phospholamban and TnI, and myocyte contraction responses. In contrast, at 10 microM isoproterenol, despite the negative effect of PDE4, cAMP accumulation is sufficient for maximal PKA phosphorylation of phospholamban and TnI. Inhibition of PDE4 with rolipram enhances cAMP accumulation, but not PKA phosphorylation and contraction responses. It is interesting that activities of both PKA and protein phosphatase 2A (PP2A) are enhanced under beta(1)AR activation with 10 microM isoproterenol, and PP2A is recruited to PKA/A kinase-anchoring protein complex. Inhibition of PP2A with okadaic acid further enhances the phosphorylation of phospholamban and TnI as well as contraction responses induced by 10 microM isoproterenol. Therefore, PP2A plays a key role in limiting PKA phosphorylation of phospholamban and TnI for myocyte contraction responses under beta(1)AR stimulation.

SUBMITTER: De Arcangelis V

PROVIDER: S-EPMC2654611 | biostudies-literature | 2008 Nov

REPOSITORIES: biostudies-literature

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Phosphodiesterase 4 and phosphatase 2A differentially regulate cAMP/protein kinase a signaling for cardiac myocyte contraction under stimulation of beta1 adrenergic receptor.

De Arcangelis Vania V Soto Dagoberto D Xiang Yang Y

Molecular pharmacology 20080814 5

Activation of the beta adrenergic receptor (betaAR) induces a tightly controlled cAMP/protein kinase A (PKA) activity to ensure an agonist dose-dependent and saturable contraction response in animal heart. We have found that stimulation of beta(1)AR by isoproterenol induces maximal contraction responses at the dose of 1 microM in cardiac myocytes; however, cAMP accumulation continues to increase with higher agonist concentrations. Dose-dependent cAMP accumulation is tightly controlled by negativ ...[more]

PMID: 18703669

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Project description:AimsB56α is a protein phosphatase 2A (PP2A) regulatory subunit that is highly expressed in the heart. We previously reported that cardiomyocyte B56α localizes to myofilaments under resting conditions and translocates to the cytosol in response to acute β-adrenergic receptor (β-AR) stimulation. Given the importance of reversible protein phosphorylation in modulating cardiac function during sympathetic stimulation, we hypothesized that loss of B56α in mice with targeted disruption of the gene encoding B56α (Ppp2r5a) would impact on cardiac responses to β-AR stimulation in vivo.Methods and resultsCardiac phenotype of mice heterozygous (HET) or homozygous (HOM) for the disrupted Ppp2r5a allele and wild type (WT) littermates was characterized under basal conditions and following acute β-AR stimulation with dobutamine (DOB; 0.75 mg/kg i.p.) or sustained β-AR stimulation by 2-week infusion of isoproterenol (ISO; 30 mg/kg/day s.c.). Left ventricular (LV) wall thicknesses, chamber dimensions and function were assessed by echocardiography, and heart tissue collected for gravimetric, histological, and biochemical analyses. Western blot analysis revealed partial and complete loss of B56α protein in hearts from HET and HOM mice, respectively, and no changes in the expression of other PP2A regulatory, catalytic or scaffolding subunits. PP2A catalytic activity was reduced in hearts of both HET and HOM mice. There were no differences in the basal cardiac phenotype between genotypes. Acute DOB stimulation induced the expected inotropic response in WT and HET mice, which was attenuated in HOM mice. In contrast, DOB-induced increases in heart rate were unaffected by B56α deficiency. In WT mice, ISO infusion increased LV wall thicknesses, cardiomyocyte area and ventricular mass, without LV dilation, systolic dysfunction, collagen deposition or foetal gene expression. The hypertrophic response to ISO was blunted in mice deficient for B56α.ConclusionThese findings identify B56α as a potential regulator of cardiac structure and function during β-AR stimulation.

Project description:A five-state model of myofilament contraction was integrated into a well-established rabbit ventricular myocyte model of ion channels, Ca(2+) transporters and kinase signaling to analyze the relative contribution of different phosphorylation targets to the overall mechanical response driven by ?-adrenergic stimulation (?-AS). ?-AS effect on sarcoplasmic reticulum Ca(2+) handling, Ca(2+), K(+) and Cl(-) currents, and Na(+)/K(+)-ATPase properties was included based on experimental data. The inotropic effect on the myofilaments was represented as reduced myofilament Ca(2+) sensitivity (XBCa) and titin stiffness, and increased cross-bridge (XB) cycling rate (XBcy). Assuming independent roles of XBCa and XBcy, the model reproduced experimental ?-AS responses on action potentials and Ca(2+) transient amplitude and kinetics. It also replicated the behavior of force-Ca(2+), release-restretch, length-step, stiffness-frequency and force-velocity relationships, and increased force and shortening in isometric and isotonic twitch contractions. The ?-AS effect was then switched off from individual targets to analyze their relative impact on contractility. Preventing ?-AS effects on L-type Ca(2+) channels or phospholamban limited Ca(2+) transients and contractile responses in parallel, while blocking phospholemman and K(+) channel (IKs) effects enhanced Ca(2+) and inotropy. Removal of ?-AS effects from XBCa enhanced contractile force while decreasing peak Ca(2+) (due to greater Ca(2+) buffering), but had less effect on shortening. Conversely, preventing ?-AS effects on XBcy preserved Ca(2+) transient effects, but blunted inotropy (both isometric force and especially shortening). Removal of titin effects had little impact on contraction. Finally, exclusion of ?-AS from XBCa and XBcy while preserving effects on other targets resulted in preserved peak isometric force response (with slower kinetics) but nearly abolished enhanced shortening. ?-AS effects on XBCa and XBcy have greater impact on isometric and isotonic contraction, respectively.

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Phosphodiesterase 4 and phosphatase 2A differentially regulate cAMP/protein kinase a signaling for cardiac myocyte contraction under stimulation of beta1 adrenergic receptor.

Publications

Phosphodiesterase 4 and phosphatase 2A differentially regulate cAMP/protein kinase a signaling for cardiac myocyte contraction under stimulation of beta1 adrenergic receptor.

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