Chloride uptake by oat coleoptile parenchyma described by combined influx and efflux transport systems

Chloride fluxes for oat coleoptile parenchyma were measured using the MIFE system for non-invasive microelectrode ion flux measurement. The effects on chloride fluxes of membrane potential, external chloride concentration, pH , cation composition of the bathing solution, and the anion channel blocker anthracene-9-carboxylic acid were studied. From the experimental data we propose that the step-like appearance of the chloride uptake curve at concentrations higher than 1 mM is due to combined activity of influx and afflux systems. According to this hypothesis the up take of chloride ions is made by a pH sensitive active transport system wit h V-max = 4000 nmol m(-2) s(-1), K-m = 7 mM [Cl-]. Chloride ions are releas ed from the cell through channels with Gaussian type kinetics, the characte ristics of which are dependent upon the external bathing solution: V-max = -2300 nmol m(-2) s(-1) at 25 mM [Cl-] for CaCl2, and V-max = -2000 nmol m(- 2) s(-1) at 15 mM [Cl-] for KCl; with both curves having the same width of 17 mM [Cl-].