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INFLUENCE DE LA TENEUR RELATIVE EN POTASSIUM ET EN SODIUM DE MILIEU EXTÉRIEUR SUR LA DIFFÉRENCE DE POTENTIEL ÉLECTROCHIMIQUE DES CHLORURES CHEZ NITELLA

J. LEFÈBVRE and C. GILLET
Bulletin de la Société Royale de Botanique de Belgique / Bulletin van de Koninklijke Belgische Botanische Vereniging
T. 104, Fasc. 1 (1971), pp. 137-149
Stable URL: http://www.jstor.org/stable/20792795
Page Count: 13
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INFLUENCE DE LA TENEUR RELATIVE EN POTASSIUM ET EN SODIUM DE MILIEU EXTÉRIEUR SUR LA DIFFÉRENCE DE POTENTIEL ÉLECTROCHIMIQUE DES CHLORURES CHEZ NITELLA
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Abstract

Effects of the sodium and potassium external concentration on the chloride electrochemical potential difference of Nitella. — The chloride electrochemical potential difference, membrane potential and electrical resistance of Nitella flexilis were measured at 3°C and 20°C in solutions where glucuronate is progressively substituted for chloride. The predominant cation is K⁺ or Na⁺ following the experiments but the ionic strength of the medium is kept constant at 1,1 mM. Cells pretreated in Ca-free medium are used throughout the experiments. The vacuolar concentrations are 64 mM K⁺, 43 mM Na⁺ (flame photometry) and 80 mM Cl⁻ (electrotitrimetric titration). Membrane potential and resistance are little affected by variations of chloride in the external medium but large changes occur in the chloride electrochemical potential difference. The internal chloride concentration for the whole cell calculated from the values of these parameters decreases or increases with [Cl]o in an unexpected way with the reputed low permeability of the membrane to Cl ions. A double reciprocal plot of [Cl]i and [Cl]o for both the temperatures shows that the penetration of chlorides into Nitella is easier when Na⁺ is more abundant in the external medium and that this phenomenon is linked with the metabolic energy. The discrepancy between the chloride concentration measured by titration and microelectrode and the large variations of cellular chloride activity are discussed. The more likely explanation is that the thermodynamic active chlorides are only a part of the total chloride pool. The lack of effects on membrane potential is compared with the same stability observed when vacuolar sap is exchanged with artificial solutions where chlorides ions are varied.

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