Summary. Ionic channels responsible for excitation of plasmalemma and tonoplast of fresh-water Nitellopsis obtusa were studied using the voltage-clamp technique. Voltage was clamped on each separate membrane. Chloride channels were inhibited with ethacrynic acid. 1. Along with anion (chloride) channels the cation channels have been revealed in the membranes. The corresponding channels are similar in both types of membranes. 2. The cation channels are controlled by membrane voltage being activated under membrane depolarization. The channels possess activation-inactivation kinetics. For N. obtusa characteristic times of activation and inactivation are 0.1 and 0.5 sec, respectively. 3. Conductance of cation channels depends on the type of cation and the orders of conductivity decrease are the following: Rb + >K § >Cs + >Na + >Li + and Ba 2 § > Sr 2 + > Ca 2 + > Mg 2 +. Ratio of conductance for bivalent ions to that of monovalent ones decreases with the increase of normal concentrations. When the external medium contains both mono-and bivalent cations in comparable concentrations, the current is mainly determined by the latter. In natural environment of the algae such conditions are realized for Ca 2+ ions which create the bulk of the inward current through cation channels under cell excitation. That is why we term these channels "calcium" ones. 4. Ca 2 + ions entering the cytoplasm through the calcium channels located in both membranes activate the chloride channels. Ba 2+ and Mg 2+ also activate the chloride channels but to a lesser extent than Ca; § does. Characteristic inactivation time of these channels in N. obtusa is about 1 to 2 sec.

The specific complexes of human alpha-lactalbumin (alpha-LA) with oleic acid (OA), HAMLET and LA-OA-17 (OA-complexes), possess cytotoxic activity against tumor cells but the mechanism of their cell penetration remains unclear. To explore the molecular mechanisms underlying interaction of the OA-complexes with the cell membrane, their interactions with small unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles and electroexcitable plasma membrane of internodal native and perfused cells of the green alga Chara corallina have been studied. The fractionation (Sephadex G-200) of mixtures of the OA-complexes with the vesicles shows that OA-binding increases the affinity of alpha-LA to DPPC vesicles. Calcium association decreases protein affinity to the vesicles; the effect being less pronounced for LA-OA-17. The voltage clamp technique studies show that LA-OA-17, HAMLET, and their constituents produce different modifying effects on the plasmalemmal ionic channels of the Chara corallina cells. The irreversible binding of OA-complexes to the plasmalemma is accompanied by changes in the activation-inactivation kinetics of developing integral transmembrane currents, suppression of the Ca(2+) current and Ca(2+)-activated Cl(-) current, and by increase in the nonspecific K(+) leakage currents. The latter reflects development of nonselective permeability of the plasma membrane. The HAMLET-induced effects on the plasmalemmal currents are less pronounced and potentiated by LA-OA-17. The control experiments with OA and intact alpha-LA show their qualitatively different and much less pronounced effects on the transmembrane ionic currents. Thus, the modification of alpha-LA by OA results in an increase in the protein association with the model lipid bilayer and in drastic irreversible changes in permeability of several types of the plasmalemmal ionic channels.

Caz+ current recordings have been made on Nitella syncurpa cells using the intracellular perfusion and the voltage-clamp technique. TPA (12~O-tetradecanoylphorbol-13-acetate), a substance capable of activating protein kinase C from plasmalemma of Nitella cells, modulates voltage-dependent Ca *+ channels. Polymixin B, inhibitor of protein kinase C, blocks the Nitella plasmalemma Ca *+ channels; the rate of channel blockage depends on the concentration and exposure time of the substance.

The introduction of 1.5 × 10−8 − 10−6 M inositol 1,4,5‐trisphosphate (IP3) into the bathing solution of Nitella syncarpa cells induced: (i) an increase in amplitude of the inward Ca2+ current; (ii) the appearance of an inward Cl− current; (iii) a shift in the threshold for activation of the Cl− channels on hyperpolarization of the membrane to more positive values. These facts suggest that IP3 participates in the causing of changes in the intracellular free Ca2+ concentration and, hence, in the regulation of ionic channels in Nitella syncarpa plasmalemma.

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