Proceedings of The Physiological Society
University of Edinburgh (2011) Proc Physiol Soc 25, C15 and PC15
Effects of Kv7 potassium channel modulators on human intra-pulmonary artery
S. Brennan1, R. Oliveira1, A. Gurney1
1. FLS, University of Manchester, Manchester, United Kingdom.
Pulmonary arterial hypertension (PAH) is a progressive disease with increasingly debilitating symptoms and survival of only a few years (McLaughlin et al, 2004). Kv7 potassium channels were recently implicated in the regulation of membrane potential in rodent pulmonary artery smooth muscle cells (PASMC) and pulmonary artery constriction (Joshi et al 2006; Joshi et al 2009. Presumably as a consequence of this role, the Kv7 channel opener flupirtine was beneficial in two independent mouse models of PAH (Morecroft et al, 2009). To determine if Kv7 channel activation could be beneficial in humans, we have now investigated the effects of Kv7 modulators on distal pulmonary arteries isolated from human lung samples. Intra-pulmonary arteries (iPA, <1mm diameter) were dissected from normal lung tissue collected during tumour resection from lung cancer patients. RT-PCR was performed on RNA isolated from iPAs from separate patients, using primers directed against each of the five KCNQ genes that encode Kv7 channels. RT-PCR products were confirmed by sequencing. Myography experiments were conducted to measure the effects on isometric tension of the Kv7 blockers, linopirdine and XE991, and the activators, retigabine and flupirtine. pEC50 values were measured by fitting the Hill equation to concentration-effect data obtained for each vessel. All data is expressed as the mean ± S.E.M with concentrations in molar unless stated. The dependence of constrictor effects on voltage-gated calcium influx was investigated using the L-type calcium channel blocker, nifedipine. RT-PCR detected KCNQ subunits 1,3, 4 and 5, although there was variability among individual patients. The Kv7 blockers produced concentration-dependent constriction of human iPAs, with pEC50 values of 6.3 ± 0.3 (N=9) for linopirdine and 5.3 ± 0.2 (N=13) for XE991. The Kv7 openers flupirtine and retigabine both produced concentration-dependent dilation of agonist pre-constricted vessels, with pEC50 values of 4.5 ± 0.4 (N=4) and 5.3 ± 0.2 (N=4), respectively. Preliminary experiments show that 100nM nifedipine suppressed the vasoconstrictor actions of 1µM XE991 and 5µM linopirdine. We conclude that some Kv7 channel subunits are expressed at the mRNA level in human iPAs. Functional Kv7 channels are likely to be expressed in human PASMCs, because known modulators of Kv7 channel activity were able to alter the tone of the vessels in the predicted manner and constrictor effects depended on voltage-gated calcium entry into PASMC. The data therefore supports the idea of Kv7 channels as a drug target in the treatment of PAH.
Where applicable, experiments conform with Society ethical requirements