Inhibition of extracellular signal-regulated kinase (ERK) enhances β-adrenoceptor-mediated vasodilatation in porcine isolated coronary artery: role of potassium channels

Chukwuemeka Uhiara, Stephen Alexander, Richard Roberts. School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom.

We have previously shown that inhibition of ERK in porcine blood vessels enhances relaxation responses to β-adrenoceptor (β-AR) agonists (Uhiara et al., 2009). In some vessels, β-AR-induced relaxation of smooth muscle involves activation of K+ channels (Huang and Kwok, 1997) and our previous studies have suggested that the increased activation of K+ channels is involved in the ERK-mediated regulation of the relaxation. In this study, we have used selective channel blockers to determine which K+ channels are involved.

Ring segments of porcine coronary artery were prepared as previously described (Uhiara et al., 2009). Segments were pre-incubated for 45 min with either the upstream inhibitor of ERK PD98059 (50 μM) or a selective K+ channel blocker (either glibenclamide (10μM), iberiotoxin (100 nM) or TRAM-34 (10 μM)), or a combination of PD98059 and each blocker. Tissues were then pre-contracted with the thromboxane mimetic U46619 to 70-80% of the 60 mM KCl response, before they were relaxed with cumulative concentrations of the β2-AR agonist salbutamol. Effects of the drugs were assessed using one-way ANOVA followed by a Tukey post-hoc test, with data from at least five separate animals of either sex.

Application of salbutamol (10 nM – 30 μM) to precontracted vessel segments induced a concentration-dependent vasodilatation. PD98059 alone shifted the concentration response curves to the left. None of the potassium channel blockers altered the salbutamol response. However, incubation with TRAM-34, but not glibenclamide or iberiotoxin, prevented the left-shift to PD98059 (pEC50 values: control = 6.1 ± 0.2, PD98059 = 6.7 ± 0.1, PD98059+TRAM-34 = 6.1 ± 0.1; P<0.05; Figure 1).

As we have previously observed, the vasodilatation response to β2-AR activation in porcine precontracted coronary artery segments was augmented by PD98059, an inhibitor of ERK activation. This phenomenon was prevented by co-incubation of PD98059 and TRAM-34, a potent inhibitor of the intermediate-conductance Ca2+-activated K+ channel (Wulff et al., 2000). Inhibitors of high-conductance Ca2+-activated K+ channels (iberiotoxin) and ATP-sensitive K+ channels (glibenclamide) did not alter the PD98059-induced enhancement of the vasodilatation response. The data suggest that the enhanced β2-AR-mediated vasodilatation may be due to an increased activity of the intermediate-conductance Ca2+-activated K+ channel in this tissue.

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