The effect of glucose on chloride uptake by Chlorella : II. Effect of intracellular acidification on chloride uptake.

Glucose at 5 mM inhibited chloride uptake by Chlorella fusca in the light and in the dark by 30±10% and acidified the cell interior by 0.2 units (measured with 5.5-dimethyl-oxazolidine-2.4-dione; DMO). Neither effect was shown by the glucose analogues 3-O-methylglucose and 6-desoxyglucose which are transported into the cell but not metabolized. As it was surmised that inhibition of Cl(-) transport was the result of intracellular acidification, the action of other agents on Cl(-) transport and intracellular pH was examined. The Tris salts of the permeant acids DMO and propionic acid inhibited Cl(-) transport. The concentration and pH dependence of this effect were consistent with the free acids being the effective agents. At pH 6.7 the 15 mM Tris salts has about the same effect on Cl(-) transport as 5 mM glucose. Under these conditions the intracellular pH (measured by the DMO method) was lowered by 0.2 units with glucose as well as, in presence of the Tris salts. When the algae were gassed with 1.5% CO2 in air, Cl(-) uptake in the light was depressed to 40-50% and the intracellular pH was lowered by 0.4 units. On the basis of these observations and the results from the preceding study, inhibition of Cl(-) transport by glucose is interpreted as inhibition of an ATP-dependent Cl(-)/OH(-) exchange by intracellular acidification, due to glucose metabolism.