title: Induced alterations in calcium uptake rate in normoxic rate proximal tubules.
abstract: This study is well-oxygenated, freshly isolated rat proximal tubules (RPT), examined the effects of several drugs that alter the transmembrane K+ and Na+ gradients across cell membranes, including valinomycin (VAL), amphotericin B (AMPHO), and ouabain (OUAB). The effects of high extracellular potassium chloride (KCl) concentrations (45 mM) and low extracellular sodium concentration (100mM) were also studied. After 10 min of drug exposure Ca2+ uptake rate (nmol/mg/min) increased from 2.7 to 3.8 with VAL (p < .02), from 2.9 to 3.7 with AMPHO (p < .05), from 3.6 to 4.1 with OUAB (p < .05), and from 3.2 to 4.8 with 45 mM KCl (p < .001). Ca2+ uptake rate was sustained at these high levels at 20 min in all treated RPT except those exposed to OUAB. LDH release averaged less than 15% in control tubules and did not increase significantly except in RPT treated with VAL, where LDH release at 10 min was 48% and at 20 min was 57% (both p < .001). Of importance, only in VAL-treated RPT did ATP decrease to low levels (6.7 nmol/mg in control to 2.0 +/- 0.3 nmol/mg in VAL, p < .001). Treatment with verapamil reduced Ca2+ uptake rates at 10 min in VAL-treated RPT (from 3.8 to 3.1, p < .02, in AMPHO-treated RPT (from 3.8 to 3.1 p < .001), in OUAB-treated tubules (from 4.0 to 3.4, p < .01), and in KCl-treated RPT (from 3.7 to 3.2, p < .01). These results indicate that acute changes in the transmembrane ion gradient in RPT are accompanied by increased Ca2+ uptake rates. Ca2+ uptake rates are also increased during O2 deprivation in RPT, a situation in which the transmembrane ion gradient is likewise altered. The increased Ca2+ uptake rate observed in the present study and during hypoxia may have a common basis, that is, altered transmembrane ion gradients or some function thereof.
authors.affiliation: Department of Medicine, University of Colorado School of Medicine, Denver 80262, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Burke
authors.forename: J K
authors.initials: JK
authors.lastname: Joseph
authors.forename: D
authors.initials: D
authors.lastname: Bunnachak
authors.forename: A
authors.initials: A
authors.lastname: Almeida
authors.forename: J F
authors.initials: JF
authors.lastname: Wetzels
authors.forename: L
authors.initials: L
authors.lastname: Yu
authors.forename: A
authors.initials: A
authors.lastname: Kribben
authors.forename: E
authors.initials: E
authors.lastname: Wieder
authors.forename: R W
authors.initials: RW
authors.lastname: Schrier
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D007476:Ionophores; D014634:Valinomycin; D010042:Ouabain; D000666:Amphotericin B; D000255:Adenosine Triphosphate; D012964:Sodium; D007770:L-Lactate Dehydrogenase; D011188:Potassium; D002118:Calcium