Characterization of ERK1/2 signalling pathways induced by adenosine receptor subtypes in newborn rat cardiomyocytes

Adenosine A 1 , A 2A , and A 3 receptors (ARs) and extracellular signal‐regulated kinase 1/2 (ERK1/2) play a major role in myocardium protection from ischaemic injury. In this study, we have characterized the adenosine receptor subtypes involved in ERK1/2 activation in newborn rat cardiomyocytes. Adenosine (nonselective agonist), CPA (A 1 ), CGS 21680 (A 2A ) or Cl‐IB‐MECA (A 3 ), all increased ERK1/2 phosphorylation in a time‐ and dose‐dependent manner. The combined maximal response of the selective agonists was similar to adenosine alone. Theophylline (nonselective antagonist) inhibited completely adenosine‐mediated ERK1/2 activation, whereas a partial inhibition was obtained with DPCPX (A 1 ), ZM 241385 (A 2A ), and MRS 1220 (A 3 ). PD 98059 (MEK1; ERK kinase inhibitor) abolished all agonist‐mediated ERK1/2 phosphorylation. Pertussis toxin (PTX, G i/o blocker) inhibited completely CPA‐ and partially adenosine‐ and Cl‐IB‐MECA‐induced ERK1/2 activation. Genistein (tyrosine kinase inhibitor) and Ro 318220 (protein kinase C, PKC inhibitor) partially reduced adenosine, CPA and Cl‐IB‐MECA responses, without any effect on CGS 21680‐induced ERK1/2 phosphorylation. H89 (protein kinase A, PKA inhibitor) abolished completely CGS 21680 and partially adenosine and Cl‐IB‐MECA responses, without any effect on CPA response. Cl‐IB‐MECA‐mediated increases in cAMP accumulation suggest that A 3 AR‐induced ERK1/2 phosphorylation involves adenylyl cyclase activation via phospholipase C (PLC) and PKC stimulation. In summary, we have shown that ERK1/2 activation by adenosine in cardiomyocytes results from an additive stimulation of A 1 , A 2A , and A 3 ARs, which involves G i/o proteins, PKC, and tyrosine kinase for A 1 and A 3 ARs, and Gs and PKA for A 2A ARs. Moreover, the A 3 AR response also involves a cAMP/PKA pathway via PKC activation.British Journal of Pharmacology (2004) 141 , 329–339. doi: 10.1038/sj.bjp.0705614