Effect of Kv7.1 blockers on vascular smooth muscle contractility in conduit and resistance rat arteries

Preet Chadha1, Rob Towart2, Joannes Linders2, Iain Greenwood1. 1St George\'s (University of London), Division of Biomedical Sciences, SW17 0RE, London, United Kingdom, 2RCO-EU, J&J Pharmaceutical R & D, Janssen Pharmaceutica, Beerse, Belgium.

KCNQ1-encoded voltage-dependent potassium channels (Kv7.1) contribute to the repolarization of the cardiac action potential in cardiac myocytes. Hence, the potential proarrhythmic effects of Kv7.1 blockers are well recognised. However, the expression of Kv7 channels in smooth muscle cells has raised the possibility that Kv7.1 may play a role in regulating smooth muscle contractility. The present study investigates the effects of Kv7.1 blockers (L768,673, HMR1556 and JNJ-39490282) on vascular smooth muscle reactivity in rat conduit and resistance arteries.

Thoracic aorta (TA), mesenteric artery (MA), renal artery (RA) and intrapulmonary artery (IPA) were isolated from male Wistar rats (200-225 g) and mounted on an isometric tension myograph. Arteries were placed under a tension equivalent to that generated at 0.9 times the diameter of the vessel at 100 mmHg (TA, MA and RA) or 20 mmHg (IPA). Responses to KCl (60 mM) and methoxamine (10 nM – 30 µM in TA, MA, RA) or U46619 (1 nM – 1 µM in IPA) were assessed in the absence and presence of selective Kv7.1 blockers (L768,673, HMR1556 and JNJ282) or non-selective Kv7 blockers (linopirdine or XE991).

The selective Kv7.1 blockers (10 µM L768,673; 10 µM HMR1556; 1 and 10 µM JNJ282) had no contractile effects in rat arteries. In comparison, the non-selective Kv7 blocker linopirdine (10 µM) induced robust contractions in TA and RA. In MA and IPA, ∼10% pre-tone was required in order to provoke contraction to 10 µM linopirdine or XE991. Under similar conditions, Kv7.1 blockers did not constrict these vessels. Linopirdine augmented constrictor (methoxamine/U46619) responses in all arteries examined. Conversely, L768,673 (10 µM), HMR1556 (10 µM) and JNJ282 (1 µM) did not alter constrictor responses. Incubation of all vessels with 10 µM JNJ282 caused a significant attenuation in both methoxamine and KCl-induced contractile responses.

The present data suggest that Kv7.1 channels do not influence vascular smooth muscle contractility. Contractile responses to linopirdine and XE991 can thus be attributed to other Kv7 channel subtypes expressed in smooth muscle cells, most likely Kv7.4 or Kv7.5 (Greenwood and Ohya, 2009; bjp, 156, 1196-1203). Blockade of Kv7.1 channels in studies in vivo is unlikely to have major vascular side-effects. However the potent Kv7.1 blocker (IC50 = 1 nM) JNJ282 at higher concentrations (10 µM) may also inhibit calcium channels.