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Old 12-07-2011
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Kidney Calcium in the ascending loop

How does calcium get reabsorbed
in the loop? Goljan says it's through the Na-k-2cl Co transport mechanism....but I remember Raymon mentioning while discussing diuretics in Kaplan pharm that calcium and magnesium are absorbed by getting shunted between cells due to the positive charge in the lumen.
Any one know which one is actually correct?

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Old 12-07-2011
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It is the action of Na-K-2Cl transporter. As K+ was pumped into the cell, an escape route has to be present, which allows a back leak of K+ ions into the lumen. It is called the potassium-selective channel. As the K+ leaves the cell back into the lumen, it is not accompanied by someone (kinda sad). So that's to say that there is positive charge building up in the lumen and HENCE The K+ ions drives both the Ca2+ and Mg2+ from the lumen into the interstitium via the paracellular route (in between the cells). Hope that helps.
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Yes it does...thank you :-)

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Both are correct.......In thick ascending limb of loop of henley, there is Na-K-2CL transporter. Normally this cotransporter is electrically neutral( 2 negative and 2 positive charges transported) but some amount of potassium diffuses back into lumen creating a net positive charge on the luminal side of cells. This lumen positive potential difference pushes the divalent cations(Ca & Mg) thru basolateral sides of loop cells into the interstitium. This is the absorption mechanism of Ca & Mg.
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