Effects of Ammonia and Methylamine on Cl−Transport and on the pH Changes and Circulating Electric Currents Associated with HCO3−Assimilation inChara corallina

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Abstract
Low concentrations of ammonia and methylamine greatly increase Cl− influx into Chara corallina. Both amines have their maximum effect at pH 6.5–7.5. The amine stimulation of Cl− influx is small below about pH 5.5. Above pH 8.5 there may be inhibition of influx by amines. Concentrations of 10–25 μM ammonia are sufficient to cause the maximum stimulation of Cl− influx; the corresponding methylamine concentrations are 0.1–0.2 mM. It is concluded that entry of amine cations (NH4$ and CH3NH3$), rather than unionized bases (NH3 and CH3NH2), causes Cl− transport to be increased. Increases in rates of Cl− transport are not necessarily accompanied by effects on HCO3$ assimilation and OH− efflux. Measurements of localized pH differences at the cell surface and of circulating electric currents in the bathing solution show that these phenomena are only significantly affected by ammonia at or above 50 μM and by methylamine at or above 1.0 mM. The significance of the effects of amines is assessed in relation to current ideas about transport of Cl−, HCO3−, and OH−.