KCC3a is regulated by HCO3- independently of pendrin

The inactive form of the Cl-/HCO3 exchanger - pendrin in humans results in Pendred syndrome. With dietary Na+ restriction, patients with Pendred syndrome experience significant metabolic alkalosis, hypokalemia, and lower blood pressure. K+ loss is often observed with metabolic alkalemia. K+ loss is also a significant danger for patients, especially those who are taking diuretics, have hypokalemia, or have electrolyte abnormalities. Recently, we discovered the K-Cl cotransporter-3 isoform-a (KCC3a) in intercalated cells that express pendrin. We demonstrated that loss of KCC3a decreased pendrin abundance and alkalemia increased KCC3a abundance. Our findings also suggest that Cl-, secreted by KCC3a, is recycled by pendrin, acting as a driving force for pendrin function. Based on our findings we hypothesized in this follow-up study that KCC3a is regulated by HCO3- independently of pendrin. To test our hypothesis, we examined the KCC3a abundance in pendrin knockout (KO) mice fed a Na+, K+ and Cl- deficient diet that caused K+ loss. We evaluated how the abundance of KCC3a in mice responded to HCO3- challenge with and without high salt diet. Losartan, an angiotensin II receptor type 1 antagonist, was administered to mice to explore the role of angiotensin II (Ang-II) in KCC3a-regulating signaling. To determine the role of HCO3- and aldosterone in KCC3a signaling, we also looked at how KCC3a levels changed to KCl, or K-citrate loading.On a Na+, K+, and Cl- deficient diet, KCC3a abundance was greater in pendrin-KO mice, indicating that this was the cause of the observed K+ loss. In a HCO3- challenge experiment, KCC3a abundance increased with HCO3- both with and without high salt and Losartan did not change KCC3a level, demonstrating an independent response from Ang-II. With K-citrate challenges but not with KCl loading, KCC3a abundance increased, indicating an aldosterone independent and HCO3- mediated response as citrate is metabolized to HCO3-. We also show the mouse cortical collecting duct M-1 cells express KCC3a and that expression is markedly enhanced in the presence of bicarbonate, but not alkaline pH. Taken together, our findings suggest that HCO3- is the primary signaling molecule responsible for increasing KCC3a abundance.Our results demonstrate that HCO3- is the key signaling molecule regulating KCC3a abundance and that, unlike pendrin, the response to increasing KCC3a abundance is not dependent on pendrin. NIH grants: R01DK093501 and R01DK110375, and by International Network of Excellence Leducq Foundation grant: 17CVD05. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.