Comparison of the Effects of Ammonia and Methylamine on Chloride Transport and Intracellular pH inChara corallina

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Abstract
Ammonium and methylammonium ions greatly increase the rate of Cl− transport in Chara corallian. This effect is dependent on the pH of the bathing solution. The amine-stimulated Cl− influx is small at pH 5·5, increases to a maximum at pH 6·5−7·5, and decreases again as the pH is raised to 8·5. Increased Cl− influx is accompanied by an increase in cytoplasmic pH, as calculated from the distribution of DMO. When the external pH lies between 5·5 and 7·3, cytoplasmic pH in the absence of amine is 7·65−7·70, with an increase of 0·15−0·25 in the presence of amine. As external pH is increased above 7·3, cytoplasmic pH also increases, with progessively less effect of amine. Although the relationship between Cl− influx and cytoplasmic pH is not simple, the results provide evidence in accord with the hypothesis that Cl− transport in Chara involves H+—Cl− symport, or the equivalent OH−—Cl− antiport. The possible role of cytoplasmic pH as a factor involved in the regulation of membrane transport in Chara is discussed.

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