{'fraction_non_alphanumeric': 0.06844281120808451, 'fraction_numerical': 0.026182820395039046, 'mean_word_length': 4.792553191489362, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Altered electrolyte homeostasis in mice with collecting‐duct‐principal‐cell select knockout of the mammalian‐target‐of‐rapamycin (mTOR)

The mammalian‐target‐of‐rapamycin (mTOR) is a central sensor of energy status in many cell types. One of its primary regulators is insulin. In cell culture, mTOR has been demonstrated to play a role in insulin activation of the epithelial sodium channel (ENaC). To assess the role of mTOR on electrolyte homeostasis by the collecting duct (CD), we generated mice with CD‐principal‐cell select mTOR knockout (KO) by Cre‐lox recombination using the aquaporin‐2 promoter to drive Cre‐recombinase. No differences in body or kidney weights between KO and wild‐type (WT) littermates were observed. Adaptation to a low‐sodium (Na+) diet was assessed in young, male mice. As compared to WT, KO mice (n = 8/genotype) fed the low Na+ diet for one‐week had significantly lower plasma potassium (K+) levels (mM): 4.97 ± 0.24 (wild‐type, WT) versus 3.89 ± 0.14 (KO), p < 0.005, with no significant differences in plasma chloride (Cl−) or Na+. Likewise, no significant differences were found between genotypes for urine excretion of Na+, K+, or Cl− on days 1–3 of the low‐Na+ diet; however, there was a strong trend for a relatively higher urine K‐to‐Cl ratio on day 2 in the KO: 1.64 ± 0.18 (WT) versus 2.26 ± 0.24 (KO), p = 0.053 suggesting impaired homeostatic balance between K+ and Na+ in the KO. A benzamil‐sensitivity test was applied to KO and WT mice, as an assessment of basal ENaC activity, by administering 4.3 mg/kg·bw benzamil, intraperitoneally, and collecting urine for 4 hours. KO mice had significantly reduced urine Cl− concentrations (mM), as well as, absolute excretion of both Na+ and Cl− (mmol/4 hours), as compared to the WT, suggesting reduced basal ENaC activity. However, their urinary ratio of Na‐to‐Cl was higher: 1.37± 0.07 (WT) versus 1.71± 0.11 (KO), p = 0.023, supporting independent and distinct regulation of these two electrolytes by the mTOR pathway. Overall, these findings support a role for mTOR in the modulation of CD electrolyte homeostasis by ENaC and related but distinct Cl− and K+ transporters and channels.