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Background and Purpose: Inwardly rectifying K+ (Kir) channels located on the basolateral membrane of epithelial cells of the distal nephron play a crucial role in K+ handling and BP control, making these channels an attractive target for the treatment of hypertension. The purpose of the present study was to determine how the inhibition of basolateral Kir4.1/Kir5.1 heteromeric K+ channel affects epithelial sodium channel (ENaC)‐mediated Na+ transport in the principal cells of cortical collecting duct (CCD). Experimental Approach The effect of fluoxetine, amitriptyline and recently developed Kir inhibitor, VU0134992, on the activity of Kir4.1, Kir4.1/Kir5.1 and ENaC were tested using electrophysiological approaches in CHO cells transfected with respective channel subunits, cultured polarized epithelial mCCDcl1 cells and freshly isolated rat and human CCD tubules. To test the effect of pharmacological Kir4.1/Kir5.1 inhibition on electrolyte homeostasis in vivo and corresponding changes in distal tubule transport, Dahl salt‐sensitive rats were injected with amitriptyline (15 mg·kg−1·day−1) for 3 days. Key Results: We found that inhibition of Kir4.1/Kir5.1, but not the Kir4.1 channel, depolarizes the cell membrane, induces the elevation of intracellular Ca2+ concentration and suppresses ENaC activity. Furthermore, we demonstrate that amitriptyline administration leads to a significant drop in plasma K+ level, triggering sodium excretion and diuresis. Conclusion and Implications: The present data uncover a specific role of the Kir4.1/Kir5.1 channel in the modulation of ENaC activity and emphasize the potential for using Kir4.1/Kir5.1 inhibitors to regulate electrolyte homeostasis and BP. [ABSTRACT FROM AUTHOR]

Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of mi RNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility. [ABSTRACT FROM AUTHOR]

There has been a resurgence of interest in the volume‐regulated anion channel (VRAC) since the recent cloning of the LRRC8A‐E gene family that encodes VRAC. The channel is a heteromer comprised of LRRC8A and at least one other family member; disruption of LRRC8A expression abolishes VRAC activity. The best‐in‐class VRAC inhibitor, DCPIB, suffers from off‐target activity toward several different channels and transporters. Considering that some anion channel inhibitors also suppress mitochondrial respiration, we systematically explored whether DCPIB inhibits respiration in wild type (WT) and LRRC8A‐knockout HAP‐1 and HEK‐293 cells. Knockout of LRRC8A had no apparent effects on cell morphology, proliferation rate, mitochondrial content, or expression of several mitochondrial genes in HAP‐1 cells. Addition of 10 µM DCPIB, a concentration typically used to inhibit VRAC, suppressed basal and ATP‐linked respiration in part through uncoupling the inner mitochondrial membrane (IMM) proton gradient and membrane potential. Additionally, DCPIB inhibits the activity of complex I, II, and III of the electron transport chain (ETC). Surprisingly, the effects of DCPIB on mitochondrial function are also observed in HAP‐1 and HEK‐293 cells which lack LRRC8A expression. Finally, we demonstrate that DCPIB activates ATP‐inhibitable potassium channels comprised of heterologously expressed Kir6.2 and SUR1 subunits. These data indicate that DCPIB suppresses mitochondrial respiration and ATP production by dissipating the mitochondrial membrane potential and inhibiting complexes I‐III of the ETC. They further justify the need for the development of sharper pharmacological tools for evaluating the integrative physiology and therapeutic potential of VRAC in human diseases. [ABSTRACT FROM AUTHOR]

Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility., (© 2014 The Authors. Published under the terms of the CC BY 4.0 license.)