Spectrophotometric detection of monovalent cation flux in cells: fluorescence microscope measurement of acetylcholine receptor-mediated ion flux in PC-12 cells.

A new and convenient spectroscopic method for measuring monovalent cation flux in cells is described. The technique is based on fluorescence quenching of an entrapped fluorophore (anthracene-1,5-dicarboxylic acid) by Cs+. A conventional fluorescence microscope can be used to measure the Cs+ flux. The usefulness of the technique is illustrated by measurement of acetylcholine receptor-mediated Cs+ flux in PC-12 cells, a sympathetic neuronal cell line. The results are the same as those obtained when radioactive tracer ions were used. The technique is applicable to any transmembrane process in which Cs+ can substitute for either Na+ or K+. The method has been developed to identify the different neurotransmitter receptors that control the translocation of monovalent cations and to locate the cells in central nervous system cell preparations that contain these receptors. The advantage of an optical method over tracer ion methods for biochemical and pharmacological studies of transmembrane processes in cells is described.