Role of Kir4.1 (Kcnj10) in the Regulation of Salt‐Induced Hypertension
Authors: Manis Anna D. , Levchenko Vladislav , Alvarez Santiago , Geurts Aron M. , Dwinell Melinda R. , Hodges Matthew R. , Staruschenko Alexander , Palygin Oleg 
Published: April 2020

In the kidney, Kir4.1 (Kcnj10) and Kir5.1 (Kcnj16) are highly expressed in the aldosterone sensitive distal nephron (ASDN), a major target for multiple hormones controlling blood pressure. These basolateral inwardly rectifying potassium channel subunits assemble to form both heteromeric Kir4.1/Kir5.1 channels and homomeric Kir4.1 channels. These channels control the transepithelial voltage, fine‐tune renal electrolyte homeostasis and contribute to long‐term blood pressure control, correspondingly. To study the role of Kir4.1 containing channels in the renal control of blood pressure, renin‐angiotensin‐aldosterone system (RAAS) balance, and salt‐sensitive (SS) hypertension, we created a Kcnj10 knockout (SSKcnj10−/−) on the Dahl SS rat background. The SSKcnj10−/− rat was created using CRISPR/Cas9 mutagenesis, resulting in a single base pair insertion in exon 2 of the Kcnj10 gene and producing a frameshift in Kir4.1 protein translation after only 26 amino acids. Homozygous SSKcnj10−/− rats were hypokalemic, had reduced heart, kidney, and body weights, and did not survive more than 3 weeks after birth. Mass spectrometry based quantification of serum RAAS peptides revealed increased Ang I (1631 vs. 560 pM), Ang 1–5 (499 vs. 69 pM), and Ang 1–7 (598 vs. 42 pM) levels in SSKcnj10−/− rats compared to age‐matched SSKcnj10+/+ controls. No differences were observed in serum Ang II, Ang III, Ang IV, or aldosterone levels. In addition, ACE activity represented by the Ang II to Ang I ratio was decreased in SSKcnj10−/− rats (0.58 vs. 1.1). The increases in alternative RAS axis peptides (Ang 1–5 and Ang 1–7) and decrease in ACE activity in SSKcnj10−/− rats are suggestive of a low blood pressure phenotype, however, their limited survival precluded blood pressure measurement. Heterozygous (SSKcnj10+/−) developed normally and showed no changes in serum electrolytes. Although survival rate of both male and female SSKcnj10+/− rats was dramatically lower compared to SSKcnj10+/+ rats, they were able to survive much longer than SSKcnj10−/− rats (21 vs. 83 days on average, respectively) with dietary K+ supplementation (HK; 1.41% K+), allowing for telemetric blood pressure measurement. We found no differences in baseline blood pressure under control conditions (LS+HK; 123±2 vs 125±4, mmHg), but salt‐induced (HS, 4% NaCl) elevations in blood pressure were significantly attenuated in SSKcnj10+/− rats fed a HS diet (149±6 vs 183±9 mmHg for SSKcnj10+/− and SSKcnj10+/+ rats, respectively). Furthermore, after 3 weeks on HS, SSKcnj10+/− rats showed decreased diuresis (25±5 vs 38±2, ml/day) and improved albuminuria (6.0±4.0 vs 17.2±7.6, Alb/Cre ratio) compared to SSKcnj10+/+ rats. Our results demonstrate that renal Kir4.1 containing channels mediate salt‐sensitive increases in blood pressure through regulation of potassium homeostasis, modulation of alternative RAS axis hormones, and control of renal salt handling in the ASDN.Support or Funding InformationSupported by the National Institutes of Health grants R35 HL135749, R56 DK121750, R24 HL114474, and F31 DK122647