title: Loop diuretic-sensitive potassium flux pathways of rat glomerular mesangial cells.
abstract: Glomerular mesangial cells are smooth muscle-like contractile cells that mediate hormonal regulation of glomerular filtration. To gain better understanding of ionic events that accompany contraction/relaxation of these cells, flux pathways of K+ and their regulation by vasoactive agents were investigated in cultured rat mesangial cells using 86Rb+ as a tracer. Of total 86Rb+ influx (16.6 +/- 0.6 nmol x mg protein -1 x min-1), 46% was inhibited by 2 mM ouabain. Loop diuretics inhibited 43% of ouabain-insensitive 86Rb+ influx (3.9 +/- 0.2 nmol x mg protein-1 x min-1). Half-maximum inhibition was observed at 2 and 0.4 microM for furosemide and bumetanide, respectively. Loop diuretic-sensitive 86Rb+ influx was dependent on extracellular Na+ and Cl-; a hyperbolic dependency on extracellular Na+ was noted with apparent Michaels constant of 39 mM while a sigmoidal dependency on extracellular Cl- was present, which, assuming 1:1:2 stoichiometry for Na(+)-K(+)-Cl-, produced an apparent mean affinity constant of 64 mM. Moreover, a fraction of amiloride-insensitive 22Na+ influx was found to be sensitive to furosemide and dependent on extracellular K+ and Cl-, further indicating the presence of Na(+)-K(+)-Cl- cotransport. Efflux of 86Rb+ followed first-order kinetics, of which 60% was inhibitable by furosemide. Manipulations of extracellular osmolarity revealed that these furosemide-sensitive 86Rb+ flux pathways were coordinately regulated in response to osmotic stress. Concentration-dependent stimulation of Na(+)-K(+)-Cl- cotransport-mediated 86Rb+ influx was induced by two vasoconstrictors, angiotensin II (ANG II) and arginine vasopressin (AVP), and by a vasodilator, atrial natriuretic peptide (ANP).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pediatrics, Veterans Administration Medical Center, Nashville, Tennessee.
authors.forename: T
authors.initials: T
authors.lastname: Homma
authors.forename: R L
authors.initials: RL
authors.lastname: Hoover
authors.forename: R C
authors.initials: RC
authors.lastname: Harris
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology*; D002478:Cells, Cultured; D004232:Diuretics / Q000494:pharmacology*; D005665:Furosemide / Q000494:pharmacology*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
chemical_list: D004232:Diuretics; D002034:Bumetanide; D010042:Ouabain; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D012413:Rubidium; D011188:Potassium