Potassium Transport Across the Membranes ofChara

Abstract

Smith, J. R. and Kerr, R. J. 1987. Potassium transport across the membranes of Chara. IV. Interactions with other cations.—J. exp. Bot. 38: 788–799. The ⁴²K influx ($ϕKin$) and the membrane electrical conductance (G_m were measured simultaneously for intemodal cells of Chara australis bathed in solutions containing different concentrations of various cationic species. It was found that the potassium permeability (P_k,) of the membrane was reduced significantly when the bathing [CaSO₄ exceeded 01 mol m⁻¹. Concentrations of tetra-ethylammonium ions (TEA) exceeding 0·3 mol m⁻³ were found to reduce significantly both $ϕKin$ and $ϕKoff$, but even high concentrations (10 mol m⁻³) usually did not reduce the fluxes by more than a factor of 3. Na⁺ ions were found to be capable of reducing P_K by a factor of 5·6 to a value of ∼ 4 nm s^−1. This appeared to be a minimum value for P_K which was not reduced even if several inhibitory cations were present simultaneously. This suggests that possibly only one of two different modes of K⁺ transport can be inhibited by cations. The possible geometry of the inhibitable K⁺ channel is briefly discussed and the implications of the presence of Na⁺ and Ca²⁺ ions in many common bathing solutions are considered.