Symmetric pH dependence of buffering power in giant fused cells from frog kidney proximal tubule.
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.
Bouyer
P
P
Institut National de la Santé et de la Recherche Médicale Unité 467, Faculté de Médecine Necker-Enfants Malades, Université Paris V,France.
Cougnon
M
M
Thomas
S R
SR
Hulin
P
P
Anagnostopoulos
T
T
Planelles
G
G
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
D001639:Bicarbonates; D002021:Buffers; D000643:Ammonium Chloride; D002245:Carbon Dioxide