Dissociation of parathyroid hormone and cyclic-3', 5'AMP effects on Na-Pi uptake by cells isolated from proximal straight tubules of rat kidney.
Studies in respiratory alkalotic or short-term phosphate deprived rats raised the possibility that in straight portion of proximal tubules (PST) cAMP might be not a mediator of PTH in inhibition of phosphate reabsorption. The present experiments directly compared the sensitivity of Na-dependent phosphate [32P] (Na-Pi) uptake to PTH or cAMP by PCT or PST cells freshly prepared from outer cortex and outer stripe of outer medulla of rat kidney. The purity of the cells was examined by activity of enzymes specific for PST i.e. glutamine synthetase, gamma-glutamyl transpeptidase and creatine kinase, a marker enzyme for medullary thick ascending limb (MTAL) and distal convoluted tubule. Similar inhibition of Na-Pi uptake by 1-34 bPTH by PST and PCT cells was observed: -33.0 and -30.0% (ns), respectively. In contrast, dibutyryl cAMP decreased Na-Pi uptake only by PCT but not by PST cells: -31.0 and -3.6% (p<0.02), respectively. The 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, resulted in slight stimulation of Na-Pi uptake by PST but strong inhibition by PCT cells: 7.8 vs -26.0% (p<0.001). In contrast to PCT in PST cells cAMP seems to play a minor role as a mediator of inhibition of Na-Pi uptake by PTH.
Rybczyńska
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A
Department of Clinical Chemistry, Medical Research Centre PAN, Poland.
Angielski
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S
Hoppe
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D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002469:Cell Separation; D000242:Cyclic AMP / Q000502:physiology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010281:Parathyroid Hormone / Q000494:pharmacology / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D010726:Phosphodiesterase Inhibitors; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; C025076:parathyroid hormone (1-34), bovine; D003994:Bucladesine; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine