A pertussis toxin‐sensitive mechanism of endothelin action in porcine coronary artery smooth muscle

Abstract

1 Endothelin-1 (ET-1)-induced contraction of porcine coronary artery strips may be mediated via at least two intracellular signalling mechanisims, the activation of dihydropyridine-sensitive voltage-dependent Ca²⁺ channels and the stimulation of phosphoinositide breakdown. Here we have investigated the possible involvement of pertussis toxin (PT)-sensitive guanosine-5′-triphosphate (GTP)-binding proteins (G-proteins) in ET-1-induced activation of these two signalling pathways in porcine coronary artery smooth muscle. 2 Increase in extracellular K⁺ concentration (10, 15 mm) shifted the dose-response relationship for the ET-1-induced contraction to the left. 3 The dihydropyridine Ca²⁺ channel blocker, nifedipine (10⁻⁸ m), induced a rightward shift in the dose-response curve for ET-1. Pretreatment of the arterial strips with PT (0.1 μg ml⁻¹) induced a similar rightward shift of the ET-1 dose-response curve but not of the KCl response. Nifedipine (10⁻⁸ m) did not further attenuate the ET-1-induced contraction in the PT-pretreated strips. 4 The pretreatment with PT significantly reduced ⁴⁵Ca²⁺ uptake of the arterial strips stimulated by ET-1, but had no effect on ET-1-induced production of inositol phosphates. 5 The contractile response of the arterial strips to phorbol dibutyrate, an active phorbol ester, was not significantly affected by 10⁻⁸ m nifedipine. 6 We confirmed that the pretreatment of the tissue with PT induced ADP-ribosylation of a 41 kDa membrane protein. 7 These findings indicate that activation of dihydropyridine-sensitive voltage-dependent Ca²⁺ channels by ET-1 in this tissue is mediated via a PT-sensitive G-protein in a manner apparently independent of the ET-1-induced activation of protein kinase C. It is concluded that the action of ET-1 in porcine coronary artery is mediated via two distinct signal transduction pathways, which are coupled to PT-sensitive and PT-insensitive GTP-binding proteins, respectively.