KCNQ gene expression was previously shown in various rodent blood vessels, where the products of KCNQ4 and KCNQ5, Kv7.4 and Kv7.5 potassium channel subunits, respectively, have an influence on vascular reactivity. The aim of this study was to determine if small cerebral resistance arteries of the rat express KCNQ genes and whether Kv7 channels participate in the regulation of myogenic control of diameter. Quantitative reverse transcription polymerase chain reaction (QPCR) was undertaken using RNA isolated from rat middle cerebral arteries (RMCAs) and immunocytochemistry was performed using Kv7 subunit-specific antibodies and freshly isolated RMCA myocytes. KCNQ4 message was more abundant than KCNQ5 = KCNQ1, but KCNQ2 and KCNQ3 message levels were negligible. Kv7.1, Kv7.4 and Kv7.5 immunoreactivity was present at the sarcolemma of freshly isolated RMCA myocytes. Linopirdine (1 μm) partially depressed, whereas the Kv7 activator S-1 (3 and/or 20 μm) enhanced whole-cell Kv7.4 (in HEK 293 cells), as well as native RMCA myocyte Kv current amplitude. The effects of S-1 were voltage-dependent, with progressive loss of stimulation at potentials of >−15 mV. At the concentrations employed linopirdine and S-1 did not alter currents due to recombinant Kv1.2/Kv1.5 or Kv2.1/Kv9.3 channels (in HEK 293 cells) that are also expressed by RMCA myocytes. In contrast, another widely used Kv7 blocker, XE991 (10 μm), significantly attenuated native Kv current and also reduced Kv1.2/Kv1.5 and Kv2.1/Kv9.3 currents. Pressurized arterial myography was performed using RMCAs exposed to intravascular pressures of 10-100 mmHg. Linopirdine (1 μm) enhanced the myogenic response at ≥20 mmHg, whereas the activation of Kv7 channels with S-1 (20 μm) inhibited myogenic constriction at >20 mmHg and reversed the increased myogenic response produced by suppression of Kv2-containing channels with 30 nm stromatoxin (ScTx1). These data reveal a novel contribution of KCNQ gene products to the regulation of myogenic control of cerebral arterial diameter and suggest that Kv7 channel activating drugs may be appropriate candidates for the development of an effective therapy to ameliorate cerebral vasospasm.

Background-Voltage-gated potassium (K ϩ ) channels encoded by KCNQ genes (Kv7 channels) have been identified in various rodent and human blood vessels as key regulators of vascular tone; however, nothing is known about the functional impact of these channels in vascular disease. We ascertained the effect of 3 structurally different activators of Kv7.2 through Kv7.5 channels (BMS-204352, S-1, and retigabine) on blood vessels from normotensive and hypertensive animals. Methods and Results-Precontracted thoracic aorta and mesenteric artery segments from normotensive rats were relaxed by all 3 Kv7 activators, with potencies of BMS-204352ϭS-1Ͼretigabine. We also tested these agents in the coronary circulation using the Langendorff heart preparation. BMS-204352 and S-1 dose dependently increased coronary perfusion at concentrations between 0.1 and 10 mol/L, whereas retigabine was effective at 1 to 10 mol/L. In addition, S-1 increased K ϩ currents in isolated mesenteric artery myocytes. The ability of these agents to relax precontracted vessels, increase coronary flow, or augment K ϩ currents was impaired considerably in tissues isolated from spontaneously hypertensive rats (SHRs). Of the 5 KCNQ genes, only the expression of KCNQ4 was reduced (Ϸ3.7 fold) in SHRs aorta. Kv7.4 protein levels were Ϸ50% lower in aortas and mesenteric arteries from spontaneously hypertensive rats compared with normotensive vessels. A similar attenuated response to S-1 and decreased Kv7.4 were observed in mesenteric arteries from mice made hypertensive by angiotensin II infusion compared with normotensive controls. Conclusions-In 2 different rat and mouse models of hypertension, the functional impact of Kv7 channels was dramatically downregulated. (Circulation. 2011;124:602-611.)Key Words: hypertension Ⅲ vasodilation Ⅲ KCNQ potassium channels Ⅲ gene expression P rimary hypertension is characterized by raised total peripheral resistance caused by increased arterial tone. 1 Evidence suggests increased vascular tone during hypertension is a result of a more depolarized membrane potential, which has been associated with a rise in intracellular calcium (Ca 2ϩ ). 2,3 As such, an understanding of the K ϩ channels that stabilize the resting membrane potential is crucial for delineating the pathogenesis of hypertension. Clinical Perspective on p 611KCNQ1-5 genes encode for voltage-gated K ϩ channels (Kv7.1 through Kv7.5, respectively) that have an established physiological role in neurons, 4 -7 cardiomyocytes, 8 cochlea, 9 and some epithelia. 10 There is now a growing appreciation that Kv7 channels are important regulators of smooth muscle contractility in rodent and human blood vessels. [11][12][13] In all blood vessels studied, KCNQ1 and KCNQ4 expression appears to dominate, 11,12,14 -18 although our laboratory has shown a truncated variant of KCNQ5 is also readily expressed. 15,19 Modulation of these channels provokes profound changes in vascular smooth muscle membrane potential and consequently vascular tone. [13][14][15][16][17]20 Thus, the non...

BACKGROUND AND PURPOSEKCNQ-encoded voltage-gated potassium channels (Kv7) have recently been identified as important anti-constrictor elements in rodent blood vessels but the role of these channels and the effects of their modulation in human arteries remain unknown. Here, we have assessed KCNQ gene expression and function in human arteries ex vivo. EXPERIMENTAL APPROACHFifty arteries (41 from visceral adipose tissue, 9 mesenteric arteries) were obtained from subjects undergoing elective surgery. Quantitative RT-PCR experiments using primers specific for all known KCNQ genes and immunohistochemsitry were used to show Kv7 channel expression. Wire myography and single cell electrophysiology assessed the function of these channels. KEY RESULTSKCNQ4 was expressed in all arteries assessed, with variable contributions from KCNQ1, 3 and 5. KCNQ2 was not detected. Kv7 channel isoform-dependent staining was revealed in the smooth muscle layer. In functional studies, the Kv7 channel blockers, XE991 and linopirdine increased isometric tension and inhibited K + currents. In contrast, the Kv7.1-specific blocker chromanol 293B did not affect vascular tone. Two Kv7 channel activators, retigabine and acrylamide S-1, relaxed preconstricted arteries, actions reversed by XE991. Kv7 channel activators also suppressed spontaneous contractile activity in seven arteries, reversible by XE991. CONCLUSIONS AND IMPLICATIONSThis is the first study to demonstrate not only the presence of KCNQ gene products in human arteries but also their contribution to vascular tone ex vivo. LINKED ARTICLEThis article is commented on by Mani and Byron, pp. 38-41 of this issue. To view this commentary visit http://dx

Abstract-Interstitial cells of Cajal (ICCs) were identified in the intact fixed media of the rabbit portal vein (RPV) using c-kit staining. The following experiments were performed using single cell preparations of the enzyme-dispersed vessel. Surviving contacts between the processes of single ICCs and the bodies of smooth muscle cells (SMCs) were observed in electron micrographs and by confocal microscopy. Spontaneous rhythmical [Ca 2ϩ ] i oscillations were observed in ICCs after loading with the calcium indicator fluo-3 and were associated with depolarizations of the ICCs recorded by tight-seal patch pipette. To investigate signal transmission from ICCs to SMCs in dispersed cell pairs, or within small surviving fragments of the ICC network, an ICC was stimulated under voltage-clamp, while changes in [Ca 2ϩ ] i in the stimulated cell as well as in a closely adjacent SMC or ICCs were monitored using fast x-y confocal imaging of fluo-3 fluorescence. After stimulation of single voltage-clamped ICC by a depolarizing step similar in duration to depolarizations associated with spontaneous [Ca 2ϩ ] i oscillations, a depolarization and transient elevation of [Ca 2ϩ ] i was observed in a closely adjacent SMCs after a delay of up to 4 seconds. In contrast, signal transmission from ICC to ICC was much faster, the delay being less than 200 ms. These results suggest that the an ICC may, in addition to generating an electrical signal (such as a slow wave) and thereby acting as a pacemaker for vascular SMCs of RPV, also release some unknown diffusible substance, which depolarizes the SMCs.