Local osmotic gradients drive the water flux associated with Na <sup>+</sup> /glucose cotransport
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Bibliographic record
Abstract
It recently was proposed [Loo, D. D. F., Zeuthen, T., Chandy, G. & Wright, E. M. (1996) Proc. Natl. Acad. Sci. USA 93, 13367--13370] that SGLT1, the high affinity intestinal and renal sodium/glucose cotransporter carries water molecules along with the cosubstrates with a strict stoichiometry of two Na(+), one glucose, and approximately 220 water molecules per transport cycle. Using electrophysiology together with sensitive volumetric measurements, we investigated the nature of the driving force behind the cotransporter-mediated water flux. The osmotic water permeability of oocytes expressing human SGLT1 (L(p) +/- SE) averaged 3.8 +/- 0.3 x 10(-4) cm x s(-1) (n = 15) and addition of 100 microM phlorizin (a specific SGLT1 inhibitor) reduced the permeability to 2.2 +/- 0.2 x 10(-4) cm x s(-1) (n = 15), confirming the presence of a significant water permeability closely associated with the cotransporter. Addition of 5 mM alpha-methyl-glucose (alpha MG) induced an average inward current of 800 +/- 10 nA at -50 mV and a water influx reaching 120 +/- 20 pL cm(-2) x s(-1) within 5-8 min. After rapidly inhibiting the Na(+)/glucose cotransport with phlorizin, the water flux remained significantly elevated, clearly indicating the presence of a local osmotic gradient (Delta pi) estimated at 16 +/- 2 mOsm. In short-term experiments, a rapid depolarization from -100 to 0 mV in the presence of alpha MG decreased the cotransport current by 94% but failed to produce a comparable reduction in the swelling rate. A mathematical model depicting the intracellular accumulation of transported osmolytes can accurately account for these observations. It is concluded that, in SGLT1-expressing oocytes, alpha MG-dependent water influx is induced by a local osmotic gradient by using both endogenous and SGLT1-dependent water permeability.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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 it