The role of ca2+ sensitisation in p2x receptor-induced contractions of rat small pulmonary artery

P2X receptors are Ca2+-permeable, ligand-gated cation channels, which are activated by ATP. In arteries, such as the rat small pulmonary artery (SPA), they elicit vasoconstriction (Chootip et al., 2002), which is dependent upon extracellular Ca2+. An increase in the sensitivity of the contractile proteins to cytoplasmic Ca2+via Rho kinase (RhoK) and protein kinase C (PKC) can also play a role in vasoconstriction. Thus, the aim of this study was to determine the involvement of Ca2+sensitisation in P2X receptor-mediated contractions of rat SPA, using the RhoK inhibitor Y27632 and PKC inhibitor GF109203X. 5 mm rings of rat SPA were mounted under isometric conditions in 1 mL organ baths at 37C and a resting tension of 0.5 g. Contractions were elicited by addition of the P2X receptor agonist a,b-meATP (10 lM) or KCl (40 mM) to the bath. Data are expressed as mean ± SEM and were compared by Student's t-test or one-way ANOVA as appropriate. a,b-meATP-induced contractions were significantly decreased by preincubation with Y27632 (10 lM, 70.5 ± 2.4% of control, n = 4) or GF109203X (10 lM, 62.8 ± 3.4% of control, n = 4) and were further depressed when the inhibitors were co-applied (37.8 ± 6.6% of control, n = 5, P < 0.01). KCl-induced contractions were also significantly decreased by Y27632 (10 lM) (77.4 ± 3.4% of control, n = 5, P < 0.05) and GF109203X (10 lM) (44.8 ± 4.7% of control, n = 4, P < 0.001). Co-application of the two inhibitors (10 lM each) had no greater effect than GF109203X alone (48.7 ± 7.0% of control, n = 10, P < 0.001). These data show that RhoK and PKC play a role in P2X-evoked contraction of SPA. This is surprising, as the activation of these enzymes is thought to be dependent upon activation of G