Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC245
Functional role of Kv7.1 channels in rat mesenteric artery
P. S. Chadha1, T. A. Jepps1, M. A. Chaudhary1, J. T. Linders2, R. Towart2, I. A. Greenwood1
1. Division of Biomedical Sciences, St George's, University of London, London, United Kingdom. 2. Center of Excellence for Cardiovascular Safety Research, Johnson & Johnson Pharmaceutical Research and Development, division of Janssen Pharmaceutica, Beerse, Belgium.
KCNQ1-encoded voltage-dependent potassium (K+) channels (Kv7.1) underlie the slow delayed rectifier potassium current (IKs) in cardiac myocytes. Recently, these channels along with Kv7.4 and Kv7.5 have been identified in vascular smooth muscle cells (Greenwood and Ohya, 2009). This study used selective IKs inhibitors and enhancers to characterise the role of Kv7.1 channels in rat mesenteric artery. In addition, we investigated their possible contribution to β-adrenoceptor-mediated vasodilatation. Third order mesenteric arteries were isolated from male Wistar rats (200-225 g). Isometric tension recordings were performed in a wire myograph. IKs inhibitors (HMR1556, L-768,673 and JNJ39490282; Towart et al., 2009) and enhancers (L-364,373 and mefenamic acid) were used to assess Kv7.1 channel functionality. Responses to isoprenaline or forskolin were measured in arteries preconstricted with 10 μM methoxamine in the presence and absence of various K+ channel blockers. Expression of KCNQ mRNA was determined using quantitative PCR. Values are presented as mean ± s.e.m., compared by two-tailed Student’s t-test. Amplicons for KCNQ1, KCNQ4 and KCNQ5 mRNA were detected readily in rat mesenteric arteries. HMR1556, L-768,673 and JNJ39490282 had no contractile effects in mesenteric arteries (under minimal tone), whereas the non-selective Kv7 blocker linopirdine caused robust contractions. In preconstricted mesenteric vessels, the IKs enhancers L-364,373 and mefenamic acid caused concentration-dependent relaxation that was fully reversed by Kv7.1 blockers. Relaxation in response to isoprenaline was attenuated in the presence of the linopirdine (10 μM; pEC50, 6.5±0.3 vs. 7.2±0.1 vehicle control; n=7-10; P<0.01). Similarly, isoprenaline-induced relaxation was reversed by 10 μM HMR1556 and L-768,673. These inhibitory effects were not mimicked by the Kv channel blocker 4-aminopyridine (1 mM) or the KATP blocker glibenclamide (10 μM). Relaxation caused by the adenylyl cyclase activator forskolin was also inhibited by linopirdine (pEC50, 7.7±0.3 vs. 8.4±0.1 vehicle control; n=3-4; P<0.001). The results from this study confirm that inhibition of Kv7.1 channels does not alter basal vascular tone. However, direct activation of Kv7.1 channels causes potent vasodilatation. Moreover, Kv7.1 channel activity appears to contribute to β-adrenoceptor-mediated relaxation in rat mesenteric artery.
Where applicable, experiments conform with Society ethical requirements