PHARMACOLOGY OF Kv7 CHANNELS IN RAT PULMONARY ARTERY

UoM administered thesis: Phd

  • Authors:
  • Mohammed Al-Chawishly

Abstract

the pulmonary artery smooth muscle cells of rat, Kv7 channels are proposed to make an important contribution to the resting membrane potential and the regulation of intrapulmonary artery (IPA) tone. Although Kv7 channels are proposed to mediate cAMP and cGMP linked vasorelaxation; the physiological modulations of their activity in pulmonary artery are not investigated. A recent study (Chadha et al., 2012a) showed that Kv7.1 activators induced relaxation in various vascular beds. However, a later study (Tsvetkov et al., 2017) showed that this relaxation was not mediated via activation of Kv7.1 channels. The aims of this study are to determine whether Kv7.1 proteins are expressed in rat IPA and if so, whether they are functional, and to investigate whether Kv7 channels contribute to cAMP and cGMP induced vasorelaxation. The aim is also to determine whether Kv7 channels have similar contributions in regulating conduit and small artery tone. The effect of pharmacological agents on vessel tension was measured by using myography. Meanwhile, the expression of Kv7 protein was validated using Western blots, and both pharmacological and siRNA knockdown approaches were used to investigate Kv7 channel function. Kv7.4 and Kv7.1 channels are identified in IPA with no detection of Kv7.5 channels. In the absence of pre-tone, Kv7.1 blocker (HMR1556) had no effect on basal tone, and application of Kv7.1 activators (RL-3 and ML277) produced marked relaxation of pre-constricted arteries, but their relaxant effects were impaired by HMR1556. Linopirdine and XE991 produced profound contraction in IPA and significantly shifted the concentration-response curve of isoprenaline and forskolin to the right without affecting the maximum response, but their effect on treprostinil induced relaxation was opposite. Pan Kv7 blockers significantly impaired the maximum response induced by glyceryl trinitrate, sodium nitroprusside and carbachol. They markedly reduced the EC50 of sildenafil without impairing the maximum response. In conduit vessels, linopirdine, sildenafil and treprostinil produced larger responses than in small vessels; however, Kv7 activators produced similar responses in different size vessels. In summary, these data show that Kv7.1 is likely to be functionally active in IPA. Data support a major role for Kv7 in cGMP, not cAMP-mediated dilation. Treprostinil acted more like the cGMP agents than cAMP in the presence of pan Kv7 blockers.

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Original languageEnglish
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Award date1 Aug 2019