SYMMETRICAL 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 f used cells from the proximal kidney tubule of the frog (Rana ridibunda ) as a function of intracellular pH (pH(i)). We monitored pH(i) and tr ansmembrane potential difference during acid or alkaline cell loading, achieved by removal of NH4Cl-containing solutions or CO2-HCO3--equili brated solutions, respectively, in the absence of extracellular Na+. D ata were well fit by the equation for a single, monoprotic buffer with a maximum beta(i) at a pH(i) of 7.39 +/- 0.06 and a total buffer conc entration of 30.7 +/- 1.6 mM (means +/- SD). From pH(i) measurements o btained during CO2-HCO3- exposure, we also calculated the buffering po wer afforded by the CO2-HCO3- pair, and we show its increasing contrib ution to total buffering power at increasing Pco(2) and pH(i). 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 buf fer with a negative logarithm of apparent dissociation constant in the normal physiological range and essentially symmetric dependence on pH (i) in both acid and alkaline ranges.