| Abstract: | Ammonium and methylammonium ions greatly increase the rate ofCl– transport in Chara corallian. This effect is dependenton the pH of the bathing solution. The amine-stimulated Cl–influx is small at pH 5·5, increases to a maximum atpH 6·5–7·5, and decreases again as the pHis raised to 8·5. Increased Cl– influx is accompaniedby an increase in cytoplasmic pH, as calculated from the distributionof 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 presenceof amine. As external pH is increased above 7·3, cytoplasmicpH also increases, with progessively less effect of amine. Although the relationship between Cl– influx and cytoplasmicpH is not simple, the results provide evidence in accord withthe 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 inthe regulation of membrane transport in Chara is discussed. |
