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, NCC, ENaC channels/transporters and RAAS in the kidney and the role of these mechanisms in 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, NCC and ENaC activity, sodium/potassium homeostasis, and the effect of a mineralocorticoid receptor inhibitors will be tested in SSKcnj10-/- and SSKcnj16-/- rats. 2) To determine if pharmacological inhibition of Kir4.1/Kir5.1 attenuates salt-induced hypertension. Our preliminary and published experiments revealed that nortriptyline, an FDA-approved second-generation tricyclic antidepressant, significantly decreases Kir4.1/Kir5.1-mediated K+- selective conductance and modulates ENaC activity in CCD cells. Using novel specific compounds, such as VU992, VU690, and VU726 in WT and SSKcnj16-/- rats, we will determine the viability of Kir4.1/Kir5.1 as a pharmacological target to regulate sodium-potassium homeostasis in the body. We hypothesize that direct modulation of basolateral Kir channel 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.
The heteromeric inwardly rectifying Kir4.1/Kir5.1 channels primary underlie the basolateral K+ conductance in the aldosterone-sensitive distal nephron. We propose that these channels are critical molecular determinants of electrolyte balance in the kidney and play an essential role in the mechanisms causing salt-sensitive hypertension and potassium imbalance. Herein, we will test this hypothesis using a combination of ex vivo and in vivo approaches, newly developed pharmacological tools and novel Kir4.1 and Kir5.1 knockouts generated on the background of the Dahl salt-sensitive rat.
