title: Acute hypotension induced by aortic clamp vs. PTH provokes distinct proximal tubule Na+ transporter redistribution patterns.
abstract: Renal parathyroid hormone (PTH) action is often studied at high doses (100 microg PTH/kg) that lower mean arterial pressure significantly, albeit transiently, complicating interpretation of studies. Little is known about the effect of acute hypotension on proximal tubule Na(+) transporters. This study aimed to determine the effects of acute hypotension, induced by aortic clamp or by high-dose PTH (100 microg PTH/kg), on renal hemodynamics and proximal tubule Na/H exchanger isoform 3 (NHE3) and type IIa Na-P(i) cotransporter protein (NaPi2) distribution. Subcellular distribution was analyzed in renal cortical membranes fractionated on sorbitol density gradients. Aortic clamp-induced acute hypotension (from 100 +/- 3 to 78 +/- 2 mmHg) provoked a 62% decrease in urine output and a significant decrease in volume flow from the proximal tubule detected as a 66% decrease in endogenous lithium clearance. There was, however, no significant change in glomerular filtration rate (GFR) or subcellular distribution of NHE3 and NaPi2. In contrast, high-dose PTH rapidly (<2 min) decreased arterial blood pressure to 51 +/- 3 mmHg, decreased urine output, and shifted NHE3 and NaPi2 out of the low-density membranes enriched in apical markers. PTH at much lower doses (<1.4 microg.kg(-1).h(-1)) did not change blood pressure and was diuretic. In conclusion, acute hypotension per se increases proximal tubule Na(+) reabsorption without changing NHE3 or NaPi2 subcellular distribution, indicating that trafficking of transporters to the surface is not the likely mechanism; in comparison, hypotension secondary to high-dose PTH blocks the primary diuretic effect of PTH but does not inhibit the PTH-stimulated redistribution of NHE3 and NaPi2 to the base of the microvilli.
authors.affiliation: Dept. of Physiology and Biophysics, Univ. of Southern California Keck School of Medicine, 1333 San Pablo St., Los Angeles, CA 90089-9142, USA.
authors.forename: Patrick K K
authors.initials: PK
authors.lastname: Leong
authors.forename: Li E
authors.initials: LE
authors.lastname: Yang
authors.forename: Harrison W
authors.initials: HW
authors.lastname: Lin
authors.forename: Niels H
authors.initials: NH
authors.lastname: Holstein-Rathlou
authors.forename: Alicia A
authors.initials: AA
authors.lastname: McDonough
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D003250:Constriction; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005919:Glomerular Filtration Rate; D007022:Hypotension / Q000139:chemically induced* / Q000503:physiopathology*; D015151:Immunoblotting; D007677:Kidney Function Tests; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010281:Parathyroid Hormone / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D010281:Parathyroid Hormone; C493556:Slc34a1 protein, rat; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D012964:Sodium; D000242:Cyclic AMP