Abstract

Spatiotemporal regulation of cAMP in cardiac myocytes is integral to regulating the diverse functions downstream of β-adrenergic stimulation. The activities of cAMP phosphodiesterases modulate critical and well-studied cellular processes. Recently, in epithelial and smooth muscle cells, it was found that the multi-drug resistant protein 4 (MRP4) acts as a cAMP efflux pump to regulate intracellular cAMP levels and alter effector function, including activation of the cAMP-stimulated Cl(-) channel, CFTR (cystic fibrosis transmembrane conductance regulator). In the current study we investigated the potential role of MRP4 in regulating intracellular cAMP and β-adrenergic stimulated contraction rate in cardiac myocytes. Cultured neonatal ventricular myocytes were used for all experiments. In addition to wildtype mice, β(1)-, β(2)-, and β(1)/β(2)-adrenoceptor, and CFTR knockout mice were used. MRP4 expression was probed via Western blot, intracellular cAMP was measured by fluorescence resonance energy transfer, while the functional role of MRP4 was assayed via monitoring of isoproterenol-stimulated contraction rate. We found that MRP4 is expressed in mouse neonatal ventricular myocytes. A pharmacological inhibitor of MRP4, MK571, potentiated submaximal isoproterenol-stimulated cAMP accumulation and cardiomyocyte contraction rate via β(1)-adrenoceptors. CFTR expression was critical for submaximal isoproterenol-stimulated contraction rate. Interestingly, MRP4-dependent changes in contraction rate were CFTR-dependent, however, PDE4-dependent potentiation of contraction rate was CFTR-independent. We have shown, for the first time, a role for MRP4 in the regulation of cAMP in cardiac myocytes and involvement of CFTR in β-adrenergic stimulated contraction. Together with phosphodiesterases, MRP4 must be considered when examining cAMP regulation in cardiac myocytes.

Links

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Publisher Full Text

Authors

Sellers ZM, Naren AP, Xiang Y, Best PM

Institution

Department of Molecular and Integrative Physiology, University of Illinois, Urbana-Champaign, Urbana, IL, USA. zselle2@illinois.edu

Source

European journal of pharmacology 681:1-3 2012 Apr 15 pg 80-7

MeSH

Animals
Animals, Newborn
Cells, Cultured
Cyclic AMP
Cystic Fibrosis Transmembrane Conductance Regulator
Gene Expression
Heart Ventricles
Isoproterenol
Mice
Mice, Inbred C57BL
Mice, Knockout
Multidrug Resistance-Associated Proteins
Myocardial Contraction
Myocytes, Cardiac
Receptors, Adrenergic, beta-1
Receptors, Adrenergic, beta-2
Signal Transduction

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22381067