Na<sup>+</sup>/H<sup>+</sup> exchanger 3 is in large complexes in the center of the apical surface of proximal tubule-derived OK cells
Bibliographic record
Abstract
Cell biological approaches were used to examine the location and function of the brush border (BB) Na(+)/H(+) exchanger NHE3 in the opossum kidney (OK) polarized renal proximal tubule cell line. NHE3 epitope tagged with the vesicular stomatitis virus glycoprotein epitope (NHE3V) was stably expressed and called OK-E3V cells. On the basis of cell surface biotinylation studies, these cells had 10-15% of total NHE3 on the BB. Intracellular NHE3V largely colocalized with Rab11 and to a lesser extent with EEA1. The BB location of NHE3V was examined by confocal microscopy relative to the lectins wheat germ aggluttinin (WGA) and phytohemagluttin E (PHA-E), as well as the B subunit of cholera toxin (CTB). The cells were pyramidal, and NHE3 was located in microvilli in the center of the apical surface. In contrast, PHA-E, WGA, and CTB were diffusely distributed on the BB. Detergent extraction showed that total NHE3V was largely soluble in Triton X-100, whereas virtually all surface NHE3V was insoluble. Sucrose density gradient centrifugation demonstrated that total NHE3V migrated at the same size as approximately 400- and approximately 900-kDa standards, whereas surface NHE3V was enriched in the approximately 900-kDa form. Under basal conditions, NHE3 cycled between the cell surface and the recycling pathway through a phosphatidylinositol (PI) 3-kinase-dependent mechanism. Measurements of surface and intracellular pH were obtained by using FITC-WGA. Internalization of FITC-WGA occurred largely into the juxtanuclear compartment that contained Rab11 and NHE3V. pH values on the apical surface and in endosomes in the presence of the NHE3 blocker, S3226, were elevated, showing that NHE3 functioned to acidify both compartments. In conclusion, NHE3V in OK cells exists in distinct domains both in the center of the apical surface and in a juxtanuclear compartment. In the BB fraction, NHE3 is largely in the detergent-insoluble fraction in lipid rafts and/or in large heterogenous complexes ranging from approximately 400 to approximately 900 kDa.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".