Interaction of ion-transport mechanisms at the plasmalemma of plant cells

Abstract

At the plasmalemma of freshwater Characeae alga Nitella flexilis, using microelectrode techniques, the membrane mechanisms of ion transport (H⁺ ATPase pump, potassium channels, unselective ionic leakage) were studied with the aim to clarify the structural bases of their interaction and regulation. It was shown that activation of a pump decreases conductance of outward-rectifying potassium channels. Also the reverse effect was detected: blocking of potassium channels by tetraethylammonium causes electrogenic pump activation. The basic ion transport mechanisms were assumed to be located separately at the plasmalemma because of the discrete nature of the molecule structures, and may interact by superposition of local electric fields, generated by each of the ion-transport mechanisms. So the intra-membrane electrical field may vary for different plasmalemma sites. A quantitative model based on the above-mentioned notions was developed. The adequacy of the model was demonstrated. The model describes steady-state non-equilibrium distribution of univalent sodium, cesium, and divalent strontium between cell and medium under different conditions. This let us refuse the traditional suggestion, that “non-equilibrium” distribution of ions is supported by active transport of them.