Proteinase-activated receptors 1 and 2 and the regulation of porcine coronary artery contractility: a role for distinct tyrosine kinase pathways

Background and Purpose

Because angiotensin-II-mediated porcine coronary artery (PCA) vasoconstriction is blocked by protein tyrosine kinase (PYK) inhibitors, we hypothesized that proteinase-activated receptors (PARs), known to regulate vascular tension, like angiotensin-II, would also cause PCA contractions via PYK-dependent signalling pathways.

Experimental Approach

Contractions of intact and endothelium-free isolated PCA rings, stimulated by PAR₁/PAR₂-activating peptides, angiotensin-II, PGF_2α, EGF, PDGF and KCl, were monitored with/without multiple signalling pathway inhibitors, including AG-tyrphostins AG18 (non-specific PYKs), AG1478 (EGF-receptor kinase), AG1296 (PDGF receptor kinase), PP1 (Src kinase), U0126 and PD98059 (MEK/MAPKinase kinase), indomethacin/SC-560/NS-398 (COX-1/2) and L-NAME (NOS).

Key Results

AG18 inhibited the contractions induced by all the agonists except KCl, whereas U0126 attenuated contractions induced by PAR₁/PAR₂ agonists, EGF and angiotensin-II, but not by PGF_2α, the COX-produced metabolites of arachidonate and KCl. PP1 only affected the responses to PAR₁/PAR₂-activating peptides and angiotensin-II. The EGF-kinase inhibitor, AG1478, attenuated contractions initiated by the PARs (PAR₂ >> PAR₁) and EGF itself, but not by angiotensin-II, PGF_2α or KCl. COX-1/2 inhibitors blocked the contractions induced by all the agonists, except KCl and PGF_2α.

Conclusion and Implications

PAR_1/2-mediated contractions of the PCA are dependent on Src and MAPKinase and, in part, involve EGF-receptor-kinase transactivation and the generation of a COX-derived contractile agonist. However, the PYK signalling pathways used by PARs are distinct from each other and from those triggered by angiotensin-II and EGF. These signalling pathways may be therapeutic targets for managing coagulation-proteinase-induced coronary vasospasm.