Entry of Methylammonium and Ammonium Ions intoCharaInternodal Cells

This is the authors' abstract. We don't add key points for this paper.

Low concentrations of ammonia and methylamine greatly affect membrane transport by, and the electrical properties of, cells of Chara corallina (=C. australis). In the presence of these amines, influx of Cl− and efflux of K+ increase and a large depolarizing current flows through the cell membrane. Measurements with [14C]methylamine show that methylamine is absorbed rapidly over a wide pH range, and that the absorption isotherm is complex. Methylamine influx is not affected by presence or absence of Cl−, K+, or Na+, but is decreased by addition of NH4+⁠. The depolarizing current is associated with a small increase in membrane conductance, except at high pH, and both these effects are reversible. The current shows saturation with increasing amine concentration; when methylamine is 10–12 times more concentrated than ammonia, it produces a current of the same magnitude. The results show that the amines enter the cells as cations (⁠NH4+ or CH3NH3+⁠) except where external pH is high, and that a specific, selective electrogenic porter is involved. There is no need to invoke active transport, as there is no evidence that internal amine concentrations exceed the equilibrium (Nernst) concentrations.