Genetic Deficit of SK3 and IK1 Channels Disrupts the Endothelium-Derived Hyperpolarizing Factor Vasodilator Pathway and Causes Hypertension

Abstract

Background-It has been proposed that activation of endothelial SK3 (K Ca 2.3) and IK1 (K Ca 3.1) K ϩ channels plays a role in the arteriolar dilation attributed to an endothelium-derived hyperpolarizing factor (EDHF). However, our understanding of the precise function of SK3 and IK1 in the EDHF dilator response and in blood pressure control remains incomplete. To clarify the roles of SK3 and IK1 channels in the EDHF dilator response and their contribution to blood pressure control in vivo, we generated mice deficient for both channels. Methods and Results-Expression and function of endothelial SK3 and IK1 in IK1Ϫ/Ϫ /SK3 T/T mice was characterized by patch-clamp, membrane potential measurements, pressure myography, and intravital microscopy. Blood pressure was measured in conscious mice by telemetry. Combined IK1/SK3 deficiency in IK1Ϫ/Ϫ /SK3 T/T (ϩdoxycycline) mice abolished endothelial K Ca currents and impaired acetylcholine-induced smooth muscle hyperpolarization and EDHFmediated dilation in conduit arteries and in resistance arterioles in vivo. IK1 deficiency had a severe impact on acetylcholine-induced EDHF-mediated vasodilation, whereas SK3 deficiency impaired NO-mediated dilation to acetylcholine and to shear stress stimulation. As a consequence, SK3/IK1-deficient mice exhibited an elevated arterial blood pressure, which was most prominent during physical activity. Overexpression of SK3 in IK1Ϫ/Ϫ /SK3 T/T mice partially restored EDHF-and nitric oxide-mediated vasodilation and lowered elevated blood pressure. The IK1-opener SKA-31 enhanced EDHF-mediated vasodilation and lowered blood pressure in SK3-deficient IK1 ϩ/ϩ /SK3 T/T (ϩdoxy-cycline) mice to normotensive levels. Conclusions-Our study demonstrates that endothelial SK3 and IK1 channels have distinct stimulus-dependent functions, are major players in the EDHF pathway, and significantly contribute to arterial blood pressure regulation. Endothelial K Ca channels may represent novel therapeutic targets for the treatment of hypertension.

Recycling of the Ca2+-activated K+ Channel, KCa2.3, Is Dependent upon RME-1, Rab35/EPI64C, and an N-terminal Domain

“…Indeed, uncoupling of the gap junctions attenuated the acetylcholine-induced hyperpolarization of the underlying smooth muscle, consistent with a direct current flow between cells (10). Recent evidence, using double KCa2.3/ KCa3.1 knock-out mice, demonstrates that KCa3.1 deficiency attenuates the acetylcholine-induced, EDHF-mediated vasodilation, whereas KCa2.3 knock-out impairs the NO-mediated dilation induced by acetylcholine (9). Additionally, KCa3.1 appears to play a critical role in the propagation of the acetylcholine-induced dilation along the arterioles (13).…”

“…Similarly, Kohler and co-workers (8) demonstrated that the targeted knock-out of KCa3.1 in mice resulted in an attenuated endothelium-derived hyperpolarizing factor (EDHF) 2 response and mild arterial hypertension. Recent studies using mice deficient in both KCa2.3 and KCa3.1 have confirmed the critical role these channels play in the EDHF response and hence blood pressure regulation (9).…”

Low intravascular pressure activates endothelial cell TRPV4 channels, local Ca 2+ events, and IK Ca channels, reducing arteriolar tone

“…The underlying hyperpolarization is generated by two subtypes of K Ca channels found in the EC, but not SMC, membrane, the small (SK Ca ,K Ca 2.3) and intermediate (IK Ca, K Ca 3.1) conductance forms that may be activated independently of each other (3). The physiological importance of independent activation is apparent from studies with K Ca 3.1-deficient mice in which the mean blood pressure is raised by ∼7 mmHg, but further elevated by disrupting both K Ca channels (4). In mesenteric resistance arteries, IK Ca channels are focused within EC projections through the internal elastic lamina (IEL) termed myoendothelial junctions (MEJs).…”

Pharmacological gating modulation of small- and intermediate-conductance Ca2+-activated K+channels (KCa2.x and KCa3.1)

“…[23][24][25] In contrast, K Ca 3.1 channels in endothelial cells and cells of the immune system, such as T-lymphocytes, are activated by more global Ca 2C signals like Ca 2C released from intracellular stores or by the refilling influx through store operated Ca 2C channels like transient receptor potential channels (TRPs) and Ca 2C release activated channels (CRAC). 26,27 K Ca 3.1 is a major component of the endothelial derived hyperpolarizing (EDH) response 28,29 and important for cell proliferation and cytokine release in lymphocytes. 27,30,31 Positive Modulation of K Ca 2/K Ca 3.1 Channels…”

“…62,63 Mice deficient in K Ca 3.1 and/or K Ca 2.3 exhibit impaired EDH responses and show a~10 mmHg increase in mean arterial blood pressure, 28,29 while SKA-31 lowers blood pressure in normotensive and hypertensive mice as well as in conscious, normotensive dogs. 29,38,64 Since the blood pressure lowering effect of SKA-31 is absent in KCa3.1 ¡/¡ mice and higher doses of SKA-31 induce sedation and lower heart rate through central K Ca 2 channel activation, 65 it seems desirable to identify K Ca 3.1 selective positive gating modulators in order to help investigate whether such compounds could be developed into a new class of endothelial targeted antihypertensives. 63 This objective recently seems to have been achieved with the demonstration that the K Ca 3.1 selective SKA-121 lowers blood pressure in normotensive and hypertensive mice without affecting heart rate.…”