A patch clamp study of pharmacological and physiological regulators of large conductance calcium-activated potassium channels in arterial smooth muscle cells

In the 1980s a group of vasodilator drugs were found to possess a common mechanism which involved opening KATP channels located in the cell membrane of smooth muscle cells, leading to vasorelaxation via membrane hyperpolarisation. A number of additional K+ channels have been identified in vascular smooth muscle cells and one of these channels, the large conductance calcium-activated K+ channel (BKCa), is a promising therapeutic target.;This thesis uses the various configurations of the patch-clamp technique to examine the effects of NS1619, nitric oxide (NO) and compounds resulting from the activation of the cGMP signalling pathway by NO, on the activity of ion channels.;Using single smooth muscle cells enzymatically isolated from the rat basilar artery, NS1619 was confirmed as an effective BKCa channel opener and hyperpolarising agent. Studies of the mechanism of action of NS1619 concluded that it has a direct effect on the BKCa channel itself or an associated regulatory site, possibly leading to an increase in the Ca2+-sensitivity of the BKCa channel. NS1619 also blocked at least two other channels, voltage-activated K+ channels and DHP-sensitive Ca2+ channels, and this latter effect almost certainly explains the functional vasorelaxation produced by NS1619 actions which will certainly limit the use of NS1619 in defining physiological roles for BKCa channels.;Nitric oxide activated whole cell currents when applied to single smooth muscle cells, which were blocked by specific BKCa channel blockers. Additional experiments determined that this action of NO could not be explained by a direct effect on BKCa channels but probably occurred by a mechanism involving a phosphorylation reaction catalysed by cGMP-dependent protein kinase. This stimulatory effect of cGMP-dependent protein kinase on BKCa channels may be involved in the vasorelaxation produced by nitric oxide and nitrovasodilators.