Pendrin-null mice develop severe hypokalemia following dietary Na+ and K+ restriction: role of ENaC.

Pendrin is an intercalated cell Cl-/[Formula: see text] exchanger thought to participate in K+-sparing NaCl absorption. However, its role in K+ homeostasis has not been clearly defined. We hypothesized that pendrin-null mice will develop hypokalemia with dietary K+ restriction. We further hypothesized that pendrin knockout (KO) mice mitigate urinary K+ loss by downregulating the epithelial Na+ channel (ENaC). Thus, we examined the role of ENaC in Na+ and K+ balance in pendrin KO and wild-type mice following dietary K+ restriction. To do so, we examined the relationship between Na+ and K+ balance and ENaC subunit abundance in K+-restricted pendrin-null and wild-type mice that were NaCl restricted or replete. Following a NaCl-replete, K+-restricted diet, K+ balance and serum K+ were similar in both groups. However, following a Na+, K+, and Cl--deficient diet, pendrin KO mice developed hypokalemia from increased K+ excretion. The fall in serum K+ observed in K+-restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. The fall in serum K+ observed in K+-restricted pendrin KO mice was enhanced with ENaC stimulation but eliminated with ENaC inhibition. However, reducing ENaC activity also reduced blood pressure and increased apparent intravascular volume contraction, since KO mice had lower serum Na+, higher blood urea nitrogen and hemoglobin, greater weight loss, greater metabolic alkalosis, and greater NaCl excretion. We conclude that dietary Na+ and K+ restriction induces hypokalemia in pendrin KO mice. Pendrin-null mice limit renal K+ loss by downregulating ENaC. However, this ENaC downregulation occurs at the expense of intravascular volume.NEW & NOTEWORTHY Pendrin is an apical Cl-/[Formula: see text] exchanger that provides renal K+-sparing NaCl absorption. The pendrin-null kidney has an inability to fully conserve K+ and limits renal K+ loss by downregulating the epithelial Na+ channel (ENaC). However, with Na+ restriction, the need to reduce ENaC for K+ balance conflicts with the need to stimulate ENaC for intravascular volume. Therefore, NaCl restriction stimulates ENaC less in pendrin-null mice than in wild-type mice, which mitigates their kaliuresis and hypokalemia but exacerbates volume contraction.

Changing Demographics of NIDDK-Funded Physician-Scientists Doing Kidney Research.

BACKGROUND AND OBJECTIVES: Although US physician-scientists have made enormous contributions to biomedical research, this workforce is thought to be getting smaller. However, among kidney researchers, changes have not been fully quantified. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We mined National Institutes of Health RePORTER to explore demographic changes of early-career and established physician and nonphysician principal investigators doing kidney-focused research. We searched for National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)-funded K series and R01 awards focused on the kidney that were active between 1990 and 2020 and determined if their emphasis was basic or clinical science. We then used public databases available on the internet to determine if these funded investigators were physicians or nonphysicians, the year in which they received either their MD (physicians) or their terminal graduate degree (nonphysicians), their sex, and whether they received their terminal degree from a US or international institution. RESULTS: Kidney-focused R01-funded principal investigators are aging, particularly among physicians. Moreover, the relative representation of physicians among both early-career and established principal investigators is falling, particularly among those doing basic science research. In contrast, the number and relative representation of nonphysician-scientists are increasing. There is also greater representation of women and international graduates among physician and nonphysician R01-funded, kidney-focused NIDDK investigators. However, although there are greater numbers of women physician principal investigators doing both basic as well as clinical research, women physician principal investigators are increasingly more likely to do clinical rather than basic science research. CONCLUSIONS: The physician-scientist workforce is increasingly made up of women and international medical graduates. However, the physician-scientist workforce is older and represents a smaller proportion of all principal investigators, particularly among those doing basic science research.