title: Effects of urinary ouabain-like factors and vanadium diascorbate on calcium mobilization in porcine inner medullary collecting duct cells: comparison with the effects of ouabain and vasopressin.
abstract: It is speculated that ouabain-like factors (OLF) play a role in the pathogenesis of volume-dependent hypertension. In previous studies we isolated a more polar OLF-1 and a more apolar OLF-2 from the urine of healthy subjects after 5 days on a high sodium intake (>400 mmol/day) by gel chromatography (Sephadex G-25 and G-10) and reverse-phase HPLC. We subsequently identified the chemical structure of OLF-2 as vanadium (V(IV)) diascorbate. OLF-1, OLF-2, and vanadium diascorbate inhibited dose-dependently porcine Na-K-ATPase in vitro. Because the inner medullary collecting duct (IMCD) plays a crucial role in the long-term regulation of body fluid volume, in the present study we investigated the effects of urinary OLF-1 and OLF-2, and of vanadium diascorbate in comparison to ouabain and vasopressin (AVP) on calcium mobilization, ie, on free calcium concentration [Ca2+]i, in cultured porcine IMCD cells. [Ca2+]i was determined by the fura-2 method in IMCD cells isolated by hypotonic treatment and density gradient centrifugation from fresh porcine kidneys. Assuming an approximate molecular weight (MW) of 400 for OLF-1 and OLF-2, OLF-1 (10(-4) mol/L) produced a slow increase in [Ca2+]i from 39 +/- 10 to 169 +/- 21 nmol/L (n = 7 ) after 4 min. Similarly, OLF-2 (10(-4) mol/L) resulted in an increase in [Ca2+]i from 74 +/- 20 to 216 +/- 52 nmol/L (n = 7) after 4 min. Vanadium diascorbate (MW 403) dose-dependently increased [Ca2+]i . At a concentration of 10(-6) mol/L it increased [Ca2+]i from 46 +/- 5 to 149 +/- 9 nmol/L (n = 5) after 4 min. A similar slow increase in [Ca2+]i was found with ouabain (10(-6) mol/L), which increased [Ca2+]i from 61 +/- 22 to 180 +/- 29 nmol/L (n = 5) after 4 min in contrast to AVP (10(-7) mol/L), which rapidly increased [Ca2+]i from 48 +/- 10 to 299 +/- 32 nmol/L (n = 4) within 30 sec. Thus, OLF-1, OLF-2, and Vanadium diascorbate, the active component of OLF-2, reveal similar effects as ouabain on IMCD cells, ie, they produce a slow increase in [Ca2+]i as expected from inhibition of Na-K-ATPase. The physiologic or pathologic roles of these and additional OLF in body fluid and blood pressure regulation and in hypertension have yet to be evaluated.
authors.affiliation: The Renal Section, Medical Policlinic, University of Bonn, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Kramer
authors.forename: A
authors.initials: A
authors.lastname: Bäcker
authors.forename: H
authors.initials: H
authors.lastname: Meyer-Lehnert
mesh_terms: D000328:Adult; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D001685:Biological Factors / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009942:Organometallic Compounds / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D012076:Renal Agents / Q000494:pharmacology; D013552:Swine; D014700:Verapamil / Q000494:pharmacology
chemical_list: D001685:Biological Factors; D002121:Calcium Channel Blockers; D009942:Organometallic Compounds; D012076:Renal Agents; C095018:vanadium diascorbate; D001127:Arginine Vasopressin; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D010042:Ouabain; D005707:Gallic Acid; D014700:Verapamil; D001205:Ascorbic Acid; D002118:Calcium