Essential role of Kir4.1/Kir5.1 channels in renal salt handling and blood pressure control

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Enhanced sensitivity of blood pressure to salt intake is present in nearly half of Americans affected by hypertension, including approximately 75% of African American hypertensive patients. Basolateral inwardly rectifying K+ (Kir) channels, specifically Kir4.1 and Kir4.1/Kir5.1 (encoded by Kcnj10 and Kcnj16 genes), play a dominant role in modulating water and electrolyte transport in the aldosterone-sensitive distal nephron. Renal Kir4.1/Kir5.1 heterotetramer is a primary basolateral channel at the distal and collecting ducts principal cells and plays an essential role in the regulation of plasma K+ level and Na+ reabsorption. The malfunction of this channel caused by genetic or medication-related factors can be directly involved in hypokalemic, hyperkalemic and hypertensive pathologies in humans. From the other side, precise pharmacological or genetic modulation of Kir4.1or Kir5.1 subunits may provide a new useful tool to the control of electrolyte balance in the body and will open new ways to treat and prevent the development of salt-sensitive hypertension and kidney damage. The Dahl Salt-Sensitive (SS) rat, a naturally occurring model of salt-sensitive hypertension, recapitulates many aspects of progressive human disease providing key insights into mechanisms underlying salt-sensitivity. We have created two rat models in which Kir4.1or Kir5.1 have been knocked out in the SS rat (SSKcnj10-/- and SSKcnj16- /- rats, respectively), enabling us to assess the role of both Kir4.1and Kir4.1/Kir5.1 channels in the control of K+ homeostasis and the development of salt-sensitive hypertension. Given the reported associations of Kir4.1/Kir5.1 with a variety of cardiorenal diseases, it is important to understand the mechanisms by which Kir4.1/Kir5.1 can influence electrolyte homeostasis, the activity of other channels and transporters, and blood pressure control in the setting of salt-induced hypertension. The Specific Aims of this proposal are 1) To define the dynamic interplay between Kir4.1/Kir5.1, ENaC channels and RAAS in the kidney and relation of these mechanisms to the control of electrolyte balance in the body. Changes in RAAS hormones under high salt and dietary potassium supplements, basolateral membrane potential in individual cells of DCT and CCD tubules, ENaC channel activity, sodium/potassium homeostasis and effect of the inhibitor mineralocorticoid (aldosterone) receptor will be tested on SSKcnj10-/- and SSKcnj16-/- rats. 2) To determine if pharmacological inhibition of Kir4.1/Kir5.1 is beneficial for salt- induced hypertension. Our preliminary experiments revealed that nortriptyline, an FDA-approved second- generation tricyclic antidepressant, significantly decreases Kir4.1/Kir5.1 -mediated K+-selective conductance and modulate ENaC activity in CCD cells. Additionally, we will use novel compounds specific for Kir4.1 channel, like VU992, in WT and SSKcnj16-/- rats to delineate the critical role of Kir channels as a pharmacological target for Na+/K+ homeostasis in the body. We hypothesize that direct modulation of basolateral Kir channels activity will play a protective role in the development of salt-induced hypertension and will lead to the discovery of more effective treatments for high blood pressure.