title: Symmetric pH dependence of buffering power in giant fused cells from frog kidney proximal tubule.
abstract: This study measures the intrinsic buffering power (beta(i)) of giant fused cells from the proximal kidney tubule of the frog (Rana ridibunda) as a function of intracellular pH (pHi). We monitored pHi and transmembrane potential difference during acid or alkaline cell loading, achieved by removal of NH4Cl-containing solutions or CO2-HCO3(-)-equilibrated solutions, respectively, in the absence of extracellular Na+. Data were well fit by the equation for a single, monoprotic buffer with a maximum beta(i) at a pHi of 7.39 +/- 0.06 and a total buffer concentration of 30.7 +/- 1.6 mM (means +/- SD). From pHi measurements obtained during CO2-HCO3- exposure, we also calculated the buffering power afforded by the CO2-HCO3- pair, and we show its increasing contribution to total buffering power at increasing PCO2 and pHi. To our knowledge, this is the first report of a cell type in which intrinsic cell buffers can be adequately approximated as a single monoprotic buffer with a negative logarithm of apparent dissociation constant in the normal physiological range and essentially symmetric dependence on pHi in both acid and alkaline ranges.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale Unité 467, Faculté de Médecine Necker-Enfants Malades, Université Paris V,France.
authors.forename: P
authors.initials: P
authors.lastname: Bouyer
authors.forename: M
authors.initials: M
authors.lastname: Cougnon
authors.forename: S R
authors.initials: SR
authors.lastname: Thomas
authors.forename: P
authors.initials: P
authors.lastname: Hulin
authors.forename: T
authors.initials: T
authors.lastname: Anagnostopoulos
authors.forename: G
authors.initials: G
authors.lastname: Planelles
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates; D002021:Buffers; D002245:Carbon Dioxide; D002459:Cell Fusion; D004563:Electrochemistry; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D008954:Models, Biological; D010477:Perfusion; D011895:Rana ridibunda
chemical_list: D001639:Bicarbonates; D002021:Buffers; D000643:Ammonium Chloride; D002245:Carbon Dioxide