title: An increase in intracellular calcium concentration that is induced by basolateral CO2 in rabbit renal proximal tubule.
abstract: Working with isolated perfused S2 proximal tubules, we asked whether the basolateral CO2 sensor acts, in part, by raising intracellular Ca2+ concentration ([Ca2+]i), monitored with the dye fura 2 (or fura-PE3). In paired experiments, adding 5% CO2/22 mM HCO3- (constant pH 7.40) to the bath (basolateral) solution caused [Ca2+]i to increase from 57 +/- 3 to 97 +/- 9 nM(n = 8, P < 0.002), whereas the same maneuver in the lumen had no effect. Intracellular pH (pHi), measured with the dye BCECF, fell by 0.54 +/- 0.08 (n = 14) when we added CO2/HCO3- to the lumen. In 14 tubules in which we added CO2/HCO3- to the bath, pHi fell by 0.55 +/- 0.11 in 9 with a high initial pHi, but rose by 0.28 +/- 0.07 in the other 5 with a low initial pHi. Thus it cannot be a pHi change that triggers the [Ca2+]i increase. Introducing to the bath an out-of-equilibrium (OOE) solution containing 20% CO2/no HCO3-/pH 7.40 caused [Ca2+]i to rise by 62 +/- 17 nM (n = 10), whereas an OOE solution containing 0% CO2/22 mM HCO3-/pH 7.40 caused only a trivial increase. Removing Ca2+ from the lumen and bath, or adding 10 microM nifedipine (L- and T-type Ca2+-channel blocker) or 2 microM thapsigargin [sarco-(endo) plasmic reticulum Ca2+-ATPase inhibitor] or 4 microM rotenone (mitochondrial inhibitor) to the lumen and bath, failed to reduce the CO2-induced increase in [Ca2+]i. Adding 10 mM caffeine (ryanodine-receptor agonist) had no effect on [Ca2+]i. Thus basolateral CO2, presumably via a basolateral sensor, triggers the release of Ca2+ from a nonconventional intracellular pool.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University, School of Medicine, 333 Cedar St., PO Box 208026, New Haven, CT 06520-8026, USA. Patrice.Bouyer@Yale.edu
authors.forename: Patrice
authors.initials: P
authors.lastname: Bouyer
authors.forename: Yuehan
authors.initials: Y
authors.lastname: Zhou
authors.forename: Walter F
authors.initials: WF
authors.lastname: Boron
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009994:Osmolar Concentration; D011817:Rabbits; D012402:Rotenone / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D012402:Rotenone; D002245:Carbon Dioxide; D002110:Caffeine; D019284:Thapsigargin; D009543:Nifedipine; D002118:Calcium