Potassium (K+) channels, with their diversity, often tissue-defined distribution, and critical role in controlling cellular excitability, have long held promise of being important drug targets for the treatment of dysrhythmias in the heart and abnormal neuronal activity within the brain. With the exception of drugs that target one particular class, ATP-sensitive K+ (KATP) channels, very few selective K+ channel activators or inhibitors are currently licensed for clinical use in cardiovascular and neurological disease. Here we review what a range of human genetic disorders have told us about the role of specific K+ channel subunits, explore the potential of activators and inhibitors of specific channel populations as a therapeutic strategy, and discuss possible reasons for the difficulty in designing clinically relevant K+ channel modulators.

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Automated patch clamp (APC) instruments enable efficient evaluation of electrophysiologic effects of drugs on human cardiac currents in heterologous expression systems. Differences in experimental protocols, instruments, and dissimilar site procedures affect the variability of IC 50 values characterizing drug block potency. this impacts the utility of Apc platforms for assessing a drug's cardiac safety margin. We determined variability of Apc data from multiple sites that measured blocking potency of 12 blinded drugs (with different levels of proarrhythmic risk) against four human cardiac currents (heRG [i Kr ], hCav1.2 [L-Type I ca ], peak hNav1.5, [Peak I na ], late hNav1.5 [Late I na ]) with recommended protocols (to minimize variance) using five APC platforms across 17 sites. IC 50 variability (25/75 percentiles) differed for drugs and currents (e.g., 10.4-fold for dofetilide block of hERG current and 4-fold for mexiletine block of hNav1.5 current). Within-platform variance predominated for 4 of 12 hERG blocking drugs and 4 of 6 hNav1.5 blocking drugs. hERG and hNav1.5 block. Bland-Altman plots depicted varying agreement across Apc platforms. A follow-up survey suggested multiple sources of experimental variability that could be further minimized by stricter adherence to standard protocols. Adoption of best practices would ensure less variable Apc datasets and improved safety margins and proarrhythmic risk assessments. The characterization of drug effects on human currents using automated patch clamp (APC) platforms employing single-or multi-hole planar patch techniques 1-5 has revolutionized the assessment of electrophysiologic (and potential proarrhythmic) effects of new drug candidates. This increasingly popular experimental approach

Key points The Ca2+ and redox‐sensing enzyme Ca2+/calmodulin‐dependent kinase 2 (CaMKII) is a crucial and well‐established signalling molecule in the heart and brain.In vascular smooth muscle, which controls blood flow by contracting and relaxing in response to complex Ca2+ signals and oxidative stress, surprisingly little is known about the role of CaMKII.The vasodilator‐induced second messenger cAMP can relax vascular smooth muscle via its effector, exchange protein directly activated by cAMP (Epac), by activating spontaneous transient outward currents (STOCs) that hyperpolarize the cell membrane and reduce voltage‐dependent Ca2+ influx. How Epac activates STOCs is unknown.In the present study, we map the pathway by which Epac increases STOC activity in contractile vascular smooth muscle and show that a critical step is the activation of CaMKII.To our knowledge, this is the first report of CaMKII activation triggering cellular activity known to induce vasorelaxation. AbstractActivation of the major cAMP effector, exchange protein directly activated by cAMP (Epac), induces vascular smooth muscle relaxation by increasing the activity of ryanodine (RyR)‐sensitive release channels on the peripheral sarcoplasmic reticulum. Resultant Ca2+ sparks activate plasma membrane Ca2+‐activated K+ (BKCa) channels, evoking spontaneous transient outward currents (STOCs) that hyperpolarize the cell and reduce voltage‐dependent Ca2+ entry. In the present study, we investigate the mechanism by which Epac increases STOC activity. We show that the selective Epac activator 8‐(4‐chloro‐phenylthio)‐2′‐O‐methyladenosine‐3′, 5‐cyclic monophosphate‐AM (8‐pCPT‐AM) induces autophosphorylation (activation) of calcium/calmodulin‐dependent kinase 2 (CaMKII) and also that inhibition of CaMKII abolishes 8‐pCPT‐AM‐induced increases in STOC activity. Epac‐induced CaMKII activation is probably initiated by inositol 1,4,5‐trisphosphate (IP3)‐mobilized Ca2+: 8‐pCPT‐AM fails to induce CaMKII activation following intracellular Ca2+ store depletion and inhibition of IP3 receptors blocks both 8‐pCPT‐AM‐mediated CaMKII phosphorylation and STOC activity. 8‐pCPT‐AM does not directly activate BKCa channels, but STOCs cannot be generated by 8‐pCPT‐AM in the presence of ryanodine. Furthermore, exposure to 8‐pCPT‐AM significantly slows the initial rate of [Ca2+]i rise induced by the RyR activator caffeine without significantly affecting the caffeine‐induced Ca2+ transient amplitude, a measure of Ca2+ store content. We conclude that Epac‐mediated STOC activity (i) occurs via activation of CaMKII and (ii) is driven by changes in the underlying behaviour of RyR channels. To our knowledge, this is the first report of CaMKII initiating cellular activity linked to vasorelaxation and suggests novel roles for this Ca2+ and redox‐sensing enzyme in the regulation of vascular tone and blood flow.

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