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KV7 potassium channels: A focus on human intra-pulmonary arteries

Brennan, Sean

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

Name of the University: The University of ManchesterCandidate’s name: Sean BrennanDegree Title: Pharmacology PhDDate: 30/09/2013Pulmonary arterial hypertension (PAH) is a disease in which pulmonary vascular resistance increases. The cell membrane of pulmonary artery smooth muscle cells (PASMC) in PAH patients is depolarised, resulting in disrupted Ca2+ signalling leading to smooth muscle constriction and PASMC proliferation and migration.In rat pulmonary artery (PA) smooth muscle the KV7 K+ channels, encoded by the KCNQ genes, have been proposed to contribute to the resting K+ current, promoting low resting tone by maintaining a negative membrane potential and low intracellular Ca2+. KV7 channel activating drugs have the potential to counteract the dysfunctional signalling during PAH by causing hyperpolarisation. This study set out to determine if the KV7 channels are expressed in human PA and if so whether they can alter vascular tone, PASMC proliferation and/or migration due to their ability to reduce intracellular Ca2+ indirectly. The effects of KV7 K+ channel modulators on human PA tone were measured using myography, while KCNQ gene expression was examined with quantitative PCR. Markers of proliferation (5-bromo-2’-deoxy-uridine (BrdU) and Ki67 antigen), were used to measure PASMC proliferation, while migration was assessed using the scratch-wound assay. Human PASMCs express all KCNQ genes, except KCNQ2. The KV7 channel blockers XE991, linopirdine and (-)chromanol 293B, constricted PAs. The KV7 channel activators retigabine and zinc pyrithione (ZnPy) relaxed PAs pre-constricted with agonists. The retigabine response was enhanced in PAs constricted with Bay K 8644, abolished in ionomycin constricted PAs and reduced in the presence of 90 mM K+, suggesting inhibition of voltage-gated Ca2+ influx. Similar experiments on rat PAs suggest that only part of the ZnPy-induced relaxation can be attributed to KV7 channel activation. The KCNQ5 gene remained in cultured PASMCs while no KV7 channel modulator altered proliferation or migration. Thus KV7.5 channels could possibly be a marker of differentiated PASMCs and/or be involved in the regulation of cell phenotype. The results imply that KV7 channels play a role in regulating PA tone and Ca2+ signalling in PA smooth. It is concluded that although KCNQ5 transcripts are preserved in proliferating PASMC, it is unlikely they play a role in PASMC proliferation or migration. In summary, KV7 channel activators may be useful in the treatment of PAH since they can prevent vasoconstriction.