Ca2+ sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure-induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) required to sustain this view is not currently available. Here, we determined whether Ca

The role of ATP-regulated K+ channels in protecting the myocardium against ischemia/reperfusion damage was explored using glibenclamide and pinacidil to block and activate the channels, respectively. Electrical and mechanical activity of arterially perfused guinea pig right ventricular walls was recorded simultaneously via an intracellular microelectrode and a force transducer. The preparations were subjected to either 1) 20 minutes of no-flow ischemia with or without glibenclamide (1 and 10 microM) followed by reperfusion, or 2) 30 minutes of no-flow ischemia with or without pinacidil (1 and 10 microM) followed by reperfusion. No-flow ischemia for 20 minutes produced changes in electrical and mechanical activity that were completely reversed on reperfusion; resting membrane potential declined by 13 +/- 1.2 mV, action potential duration at 90% repolarization (APD90) decreased by 62%, and developed tension fell by greater than 95%, but resting tension did not change significantly. Glibenclamide (10 microM) had no effect on activity during normal perfusion, but during ischemia, resting membrane potential fell slightly further (17 +/- 1.8 mV) and APD90 declined by only 24%. Developed tension declined more slowly and to a lesser extent, but resting tension rose significantly between 10 and 20 minutes of ischemia. Reperfusion of glibenclamide-treated tissues elicited arrhythmias (extrasystoles and tachycardia), and the preparations failed to recover mechanical function. Glibenclamide at 1 microM produced qualitatively similar effects, albeit less severe. After 30 minutes of no-flow ischemia in untreated tissues, resting tension increased by approximately 130% during the no-flow period. Reperfusion caused arrhythmias (extrasystoles, tachyarrhythmias, and fibrillation) and failed to restore resting or developed tension to preischemic levels. Pinacidil at 1 microM did not affect electrical or contractile function, but at 10 microM it had a negative inotropic effect, decreasing APD90 and developed tension by 5% and 18%, respectively. Both concentrations of the drug caused a faster and greater decline in APD90 during the no-flow period. Resting tension did not change during 30 minutes of no-flow ischemia in the presence of pinacidil, and reperfusion led to 85% and complete recovery of electrical and mechanical activity at 1 and 10 microM, respectively. The data indicate that glibenclamide enhances whereas pinacidil reduces myocardial damage caused by ischemia/reperfusion. The results are consistent with the hypothesis that activation of ATP-regulated K+ channels during ischemia is an important adaptive mechanism for protecting the myocardium when blood flow to the tissue is compromised.

Abstract-KCNQ4-encoded voltage-dependent potassium (Kv7.4) channels are important regulators of vascular tone that are severely compromised in models of hypertension. However, there is no information as to the role of these channels in responses to endogenous vasodilators. We used a molecular knockdown strategy, as well as pharmacological tools, to examine the hypothesis that Kv7.4 channels contribute to ␤-adrenoceptor-mediated vasodilation in the renal vasculature and underlie the vascular deficit in spontaneously hypertensive rats. Quantitative PCR and immunohistochemistry confirmed gene and protein expression of KCNQ1, KCNQ3, KCNQ4, KCNQ5, and Kv7.1, Kv7.4, and Kv7.5 in rat renal artery. Isoproterenol produced concentration-dependent relaxation of precontracted renal arteries and increased Kv7 channel currents in isolated smooth muscle cells. Application of the Kv7 blocker linopirdine attenuated isoproterenolinduced relaxation and current. Isoproterenol-induced relaxations were also reduced in arteries incubated with small interference RNAs targeted to KCNQ4 that produced a Ϸ60% decrease in Kv7.4 protein level. Relaxation to isoproterenol and the Kv7 activator S-1 were abolished in arteries from spontaneously hypertensive rats, which was associated with Ϸ60% decrease in Kv7.4 abundance. This study provides the first evidence that Kv7 channels contribute to ␤-adrenoceptor-mediated vasodilation in the renal vasculature and that abrogation of Kv7.4 channels is strongly implicated in the impaired ␤-adrenoceptor pathway in spontaneously hypertensive rats. These findings may provide a novel pathogenic link between arterial dysfunction and hypertension. The link between renal dysfunction and primary hypertension is well established, with increased renal artery resistance elevating blood pressure through the renin-angiotensin system 4 and sodium retention. 5 Moreover, it is widely recognized that altered sympathetic effects on the renal artery are strongly implicated in the initiation and perpetuation of the hypertensive state with dysfunction of the ␤-adrenoceptor pathway a dominant feature.6-11 However, little is known about the molecular mechanisms that contribute to renal artery vasospasm and decreased ␤-adrenoceptor-mediated dilation. Potassium (K ϩ ) channels regulate resting membrane potential in smooth muscle cells (SMCs) and are, thus, key determinants of smooth muscle contractility.12 Recently, our laboratory demonstrated that voltage-gated K ϩ channels encoded by KCNQ4 (Kv7.4) were drastically downregulated in the aorta and mesenteric artery of 2 different models of hypertension, spontaneously hypertensive rats (SHRs) and angiotensin II perfused mice. 13 If a similar situation occurred in the renal artery, then the associated vasospasm and arterial stenosis would lead to reduced perfusion of the kidney and activation of the renin-angiotensin system. Although KCNQ gene expression and the functional role of Kv7 channels have been established in a number of different vascular beds, [14][15][16][17][18] there...

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.