The role of extracellular signal-regulated protein kinase (ERK) in β-adrenoceptor-mediated vasodilatation in porcine coronary artery

Chukwuemeka Uhiara, Steve Alexander, Richard Roberts

University of Nottingham, Nottingham, UK

β-Adrenoceptor (β-AR)-mediated vasodilatation is known to involve a number of components, including cAMP-dependent protein kinase, nitric oxide and potassium channels (Cardillo et al., 1997; White et al. 2001) In cultured cells expressing β-ARs, isoprenaline and other β-AR ligands increase extracellular signal-regulated protein kinase (ERK) activation (Friedman et al., 2002). In this study, we have investigated the role of ERK in β-AR-mediated vasodilatation.

Hearts from pigs of either sex were obtained from a local abattoir. Ring segments from the distal portion of porcine coronary arteries were dissected and mounted in a 4-channel myograph (Danish Myotechnology Ltd.) containing Krebs-Henseleit solution gassed with O2:CO2 (95:5) at 37°C. Tension (5g wt.) was applied to the ring segments, which relaxed to a resting tension of 2-3 g wt. Tissues were pre-incubated for 45 min with the inhibitor of ERK activation, PD98059, or vehicle (0.1-0.26% DMSO v/v) and then contracted with U46619, a thromboxane receptor agonist, before relaxations were induced using cumulative concentrations of vasodilator agents. Effects of PD98059 were assessed using a paired Student’s t-test with data from at least five separate animals.

Isoprenaline (1x10-9 M – 1x10-6 M) induced a concentration-dependent vasodilatation of pre-contracted vessel segments. Pre-incubation with PD98059 (50 μM) shifted the concentration-response curve to the left (pEC50 values: control = 7.5 ± 0.1, +PD98059 = 8.1 ± 0.1; P<0.05), without significantly altering the maximal response (control 109 ± 3.1; +PD98059 122.3 ± 4.9 % relaxation). Responses to 30 μM salbutamol were also enhanced (control 54 ± 8, +PD98059 92 ± 12 % relaxation; P<0.05), while xamoterol-evoked relaxations were unaltered (pEC50 control = 5.9 ± 0.3, +PD98059 = 6.1 ± 0.1; Rmax control = 57 ± 10, +PD98059 = 61 ± 5 % relaxation). Relaxation evoked by direct activation of adenylyl cyclase using forskolin (1x10-9 M – 1x10-6 M) was also unaffected in the presence of PD98059 (pEC50 control = 7.3 ± 0.1, +PD98059 = 7.4 ± 0.1; Rmax control = 126 ± 6, +PD98059 = 115 ± 4 % relaxation).

These data indicate that ERK is able to regulate β-AR-mediated vasodilatation. Inhibition of ERK activation was associated with an enhanced response, indicating that ERK exerts an inhibitory effect on β-AR-mediated relaxation. The effect appears to be receptor subtype-dependent, since responses evoked by the β2-AR-selective agonist salbutamol, but not the β1-AR-selective agonist xamoterol, were sensitive to ERK inhibition. The lack of effect of ERK inhibition on relaxation evoked by forskolin suggests that ERK signals through a route independent of the adenylyl cyclase/cAMP/protein kinase pathway during β2-AR-mediated vasodilatation.

Cardillo C et al. (1997) Hypertension 30,918-921.

Friedman J et al. (2002) Mol Pharmacol 62, 1094-1102.

White R et al. (2001) J Pharmacol Exp Ther 298, 917-924.