Elsevier

Cell Calcium

Volume 29, Issue 5, May 2001, Pages 347-358
Cell Calcium

Regular Article
Anti-adrenergic effect of adenosine on Na+–Ca2+exchange currentrecorded from guinea-pigventricular myocytes

https://doi.org/10.1054/ceca.2001.0197Get rights and content

Abstract

The Na+–Ca2+exchanger is a protein present in the cell membrane of many cell types. In heart it plays important roles in Ca homeostasis and ionic current generation. Recently, it has been reported that the b-adrenergic agonist isoprenaline (ISO) can increase directly Na+–Ca2+exchanger activity in guinea-pig ventricular myocytes. Adenosine (ADO) exerts anti-adrenergic properties that make it effective against some arrhythmias and the aim of the present study was to determine whether or not ADO can antagonize the direct modulatory effect of ISO on the exchanger.

Whole-cell patch clamp measurements of Na+–Ca2+exchanger current (INaCa) were made from guinea-pig ventricular myocytes, with major interfering currents inhibited. INaCawas measured at 378°C as current sensitive to external nickel (Ni2+, 10 mM) during an applied descending voltage ramp. ISO (1 μM) significantly increased both inward and outward INaCa. This effect was abolished in the presence of ADO (200mM). ADO alone did not significantly alter the amplitude of INaCa. The effect of ADO on the response of INaCato ISO was mimicked by the A1ADO receptor agonist N6-cyclopentyladenosine (CPA, 10 μM), whereas the effect of ADO on the response of INaCato ISO was inhibited by the A1ADO receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 2 μM). These data suggest that the A1ADO receptor mediated the response. The anti-adrenergic effects on INaCaof ADO were not affected by the protein kinase C (PKC) inhibitor, chelerythrine (CLT, 1 μM), nor by the nitric oxide (NO) synthase inhibitor, N (G)-nitro-L-arginine methyl ester(L-NAME, 0.5 μM). Moreover, in the presence of PKC activator phorbol 12-myristate 13-acetate (PMA, 1 μM) or exogenous NO donor sodium nitroprusside (SNP, 100mM), ISO preserved its stimulatory effect on INaCa. However, prior incubation of myocytes with pertussis toxin (PTX, 5 μg ml−1did prevent the effect of ADO. The anti-adrenergic effect of ADO on INaCawas mimicked by externally applied carbachol (CCh, 10 μM), a muscarinic receptor agonist. We conclude that ADO antagonized the effect of β-adrenergic stimulation of INaCaby directly activating inhibitory G-protein (Gi)-linked A1receptors in guinea-pig ventricular myocytes. These findings may suggest a novel mechanism by which adenosine exerts some of its antiarrhythmic effects.

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    Correspondence to: J. C. Hancox, Department of Physiology and Cardiovascular Research Laboratories, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK. Tel.: +44 (0)1179289090; Fax: +44 (0)117929 3194; E-mail:[email protected]

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