Rubidium‐87 magnetic resonance spectroscopy and imaging for analysis of mammalian K<sup>+</sup> transport
Bibliographic record
Abstract
This review summarizes results 87Rb MRS/I studies of K+ transport in mammalian cells, organs and in vivo. It provides a brief description of K+ transport systems, their interactions with Rb+ and evidence that Rb+ is a best K+ congener. 87Rb MR studies have focused mostly on isolated perfused rat and pig hearts and to a lesser extent on kidney, skeletal muscle, salivary gland and red blood cells. The method has been used for three purposes: measurements of kinetics of unidirectional Rb+ uptake and efflux and steady-state Rb+ levels. In cardiovascular studies Rb+ has been used in the absence of shift reagent taking advantage of the predominantly intracellular Rb+/K+ distribution (approximately 20:1). Pharmacological analysis of Rb+ uptake and efflux allowed assessment of the contributions of various transporters to the total Rb+ fluxes in rat hearts. It was confirmed that Na+/K+ ATPase is responsible for the majority of K+ influx since Rb+ uptake is 80% ouabain-sensitive and dependent on the intracellular [Na+]. Energy deprivation caused by low-flow ischemia or metabolic inhibition reduced Rb+ uptake rate. Under normal conditions, Rb+ efflux is mediated mainly by voltage-gated K+ channels with a small contribution from the K+/Na+/2Cl- cotransporter. Intracellular alkalosis and osmotic swelling stimulated Rb+ efflux by activation of the putative K+/H+ antiporter. Activity of ATP-sensitive K+ (K(ATP)) channels was revealed by metabolic (2,4-dinitrophenol, ischemia) or pharmacological (K(ATP) opener, P-1075) stimulation of Rb+ efflux, which was reversed by the K(ATP) blocker, glibenclamide. Mitochondrial K+ transport was evaluated in hearts with saponin-permeabilized myocytes and under hypothermic conditions.Three-dimensional (3-D) spectroscopic MRI of isolated beating pig hearts has been used to obtain time series of Rb+ maps of normal and ischemic/infarcted hearts, which showed lower image intensity in the damaged area. Kinetics of Rb+ uptake in the ischemic areas depended on both regional flow and metabolism. The adrenergic agonist dobutamine stimulated Rb+ uptake in normal areas and did not affect uptake in ischemic areas. Drugs that may affect passive Rb+ transport (bumetanide, pinacidil, glibenclamide) did not change Rb+ uptake either in the normal or ischemic zones. 87Rb-MRI was also able to localize ischemia and infarction in blood-perfused hearts. 87Rb MRS/I is an excellent non-invasive research tool for studies of K+ transport in isolated organs and in vivo.
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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) | 0.002 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| 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 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".