FLOW CYTOMETRIC DETERMINATION OF INTRACELLULAR FREE POTASSIUM CONCENTRATION

A flow cytometric assay has been developed for determination of intrac ellular free potassium concentration ([K+](i)), Investigated cells, lo aded with the fluorescent pH indicator 2', 7bis-(2-carboxyethyl)-5(and -6)-carboxyfluorescein (BCECF), are incubated in the presence of niger icin, and the intracellular pH is measured, The ionophore maintains th e same ratio value [H+]/[K+] on both sides of the cytoplasmic membrane , so [K+](i) can be evaluated from the measured intracellular pH (pH(i )) and the known parameters of the buffer, Application of the method r evealed that the intracellular potassium concentration is significantl y higher in lymphocytes than in proliferating cells of HUT-78, U266, a nd JY cell lines, A surprisingly low (GO mM) [K+](i) concentration was observed with sperm cells of common carp, This method allows measurem ents on individual cells, provides data of excellent statistics, and s till does not require large amounts of material, These features offer remarkable advantages over other techniques used for intracellular Kmeasurements, such as steady-state fluorescence, atom absorption photo metry, or energy-dispersive x-ray analysis. (C) 1997 Wiley-Liss, Inc.