Ok. Babourina et al., Chloride uptake by oat coleoptile parenchyma described by combined influx and efflux transport systems, AUST J PLAN, 25(8), 1998, pp. 929-936
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-].