Abstract
Smith, J. R. and Kerr, R. J. 1987. Potassium transport across the membranes of Chara. IV. Interactions with other cations.âJ. exp. Bot. 38: 788â799. The 42K influx (â ÏKinâ ) and the membrane electrical conductance (Gm 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 (Pk,) of the membrane was reduced significantly when the bathing [CaSO4 exceeded 01 mol mâ1. Concentrations of tetra-ethylammonium ions (TEA) exceeding 0·3 mol mâ3 were found to reduce significantly both ÏKin and ÏKoffâ , but even high concentrations (10 mol mâ3) usually did not reduce the fluxes by more than a factor of 3. Na+ ions were found to be capable of reducing PK by a factor of 5·6 to a value of ⌠4 nm sâ1. This appeared to be a minimum value for PK 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.
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