title: A novel role for protein phosphatase 2A in receptor-mediated regulation of the cardiac sarcolemmal Na+/H+ exchanger NHE1.
abstract: G(q) protein-coupled receptor stimulation increases sarcolemmal Na(+)/H(+) exchanger (NHE1) activity in cardiac myocytes by an ERK/RSK-dependent mechanism, most likely via RSK-mediated phosphorylation of the NHE1 regulatory domain. Adenosine A(1) receptor stimulation inhibits this response through a G(i) protein-mediated pathway, but the distal inhibitory signaling mechanisms are unknown. In cultured adult rat ventricular myocytes (ARVM), the A(1) receptor agonist cyclopentyladenosine (CPA) inhibited the increase in NHE1 phosphorylation induced by the alpha(1)-adrenoreceptor agonist phenylephrine, without affecting activation of the ERK/RSK pathway. CPA also induced significant accumulation of the catalytic subunit of type 2A protein phosphatase (PP2A(c)) in the particulate fraction, which contained the cellular NHE1 complement; this effect was abolished by pretreatment with pertussis toxin to inactivate G(i) proteins. Confocal immunofluorescence microscopic imaging of CPA-treated ARVM revealed significant co-localization of PP2A(c) and NHE1, in intercalated disc regions. In an in vitro assay, purified PP2A(c) dephosphorylated a GST-NHE1 fusion protein containing aa 625-747 of the NHE1 regulatory domain, which had been pre-phosphorylated by recombinant RSK; such dephosphorylation was inhibited by the PP2A-selective phosphatase inhibitor endothall. In intact ARVM, the ability of CPA to attenuate the phenylephrine-induced increase in NHE1 phosphorylation and activity was lost in the presence of endothall. These studies reveal a novel role for the PP2A holoenzyme in adenosine A(1) receptor-mediated regulation of NHE1 activity in ARVM, the mechanism of which appears to involve G(i) protein-mediated translocation of PP2A(c) and NHE1 dephosphorylation.
authors.affiliation: Cardiovascular Division, King's College London, London SE1 7EH, UK.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Snabaitis
authors.forename: Richard
authors.initials: R
authors.lastname: D'Mello
authors.forename: Semjidmaa
authors.initials: S
authors.lastname: Dashnyam
authors.forename: Metin
authors.initials: M
authors.lastname: Avkiran
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D006352:Heart Ventricles / Q000187:drug effects; D007700:Kinetics; D018613:Microscopy, Confocal; D032342:Muscle Cells / Q000187:drug effects / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D051381:Rats; D043682:Receptor, Adenosine A1 / Q000187:drug effects / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000502:physiology; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D016276:Ventricular Function
chemical_list: C496899:Kcnn2 protein, rat; D043682:Receptor, Adenosine A1; D011993:Recombinant Fusion Proteins; C452850:Slc9a1 protein, rat; D051640:Small-Conductance Calcium-Activated Potassium Channels; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; C048599:N(6)-cyclopentyladenosine; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000241:Adenosine