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Doubts
1. What exactly is happening on the "luminal" side of early DCT. ?
I read that Na and Ca share the same site of reabsorption on "NaCl symport".
Is it a "passive" process of calcium reabsorption ? How ?
2.How does PTH help in reabsorption of calcium at the same site on "luminal side" by enhancing adenylate cyclase?
3. Now how does this calcium gets through the "basolateral" side by "active" transport ?
I can't visualise this . Plz help me !!
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Diagram of early distal tubule (where thiazides act ) given in kaplans pharma and goljan pathology (acid base chapter )differ from each other .
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What is the role of
1. CaST ( calcium sensing receptors ) and where are they located ? Do they have role in DCT ?
2. The protein called "calbindin" located on luminal side, what's it role? For passive transport ?
Please someone put it together for me !! Plz
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1. whats happenin is Na-Cl goes into the cell using NaCl symporter (site of thiazide action), Ca goes in using Calcium channel (PTH dependent) from the luminal side. Ca do not share same site with NaCl sympoter, they are two different channels.
2. PTH acts on basal side of cell to enhance adenyl cyclase eventually increasing cAMP which phosphorylates PTH dependent Ca channel on the luminal side such that more Ca flows into the cell.
3. Ca goes into basolateral side by secondary active transport linked to Na. It immediately exchanges itself with Na using Na-Ca antiport, and the Na that enters cell uses Na-K ATPase to exit cell against concentration gradient. So the Ca is using the energy of Na to move against concentration gradient.
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@ndprulz
Thanks so much for the time you put in solving my doubts . Now everything makes sense .
I will add one thing . Goljan (acid base electrolyte) chapter specifically mentions that ca shares the same site as Na on the symporter . That chapter also shows a figure to demonstrate the same thing .
And it mentions that "thiazides diuretics" block the Chloride part of symporter. Thus leaving the symporter open for calcium reabsorption. This is how thiazides decrease the calcium excretion and thus used in treatment of idiopathic hypercalciuria . ( so ca and Na share same site on symporter as per goljan )
