The effect of glucose on chloride uptake by Chlorella : I. General characteristics of chloride transport.

Active Cl(-) uptake by Chlorella fusca was examined by using (36)Cl as a label. Under light/air conditions chloride influx from a 2.4·10(-5) M solution was 4.0±0.04 nmol m(-2)s(-1). After 70±10 min a stationary 380±40 fold accumulation was reached. In dark/air and dark/argon influx and accumulation were reduced to 25±6%, respectively, 5±1.5% of the light/air control. Cl(-) uptake had a broad optimum around pH 7 and showed saturation kinetics with a K M of 1.25·10(-5) M and a v max of 7.0 nmol m(-2)s(-1) in light/air. Br(-) inhibited Cl(-) uptake strongly, J(-), ClO 4 (-) , SO 4 (2-) , and NO 3 (-) had no inhibitory effect. Inhibitor studies with carbonyl cyanide m-chlorophenylhydrazone and N,N'-dicyclohexylcarbodiimide resulted in a good correlation between Cl(-) uptake and ATP level. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea and darkness reduced transport activity without affecting the ATP level.The magnitudes of the pH gradient and the membrane potential across the cell membrane were determined and/or estimated under different conditions. It could be shown that in Chlorella Cl(-) transport cannot proceed via secondary active H(+)/Cl(-) cotransport. In addition, 2H(+)/Cl(-) cotransport seems unlikely for energetic reasons. On the basis of the results of this and the following study, a primary active ATP-driven Cl(-)/OH(-) exchange pump is proposed.