Although the phenotypes of many membrane-excitation mutants of Paramecium are best expressed in Na+-containing solutions, little is known about the role of Na+ in membrane excitation in Paramecium. By measuring 22Na fluxes, we have shown that: (a) The total cellular Na+ content is equivalent to a cytoplasmic concentration of 3--4 mM, if the Na+ concentration is uniform throughout the cell. (b) The kinetics of Na+ uptake can be divided into a saturable Na+ uptake with an apparent Km = 0.15 mM and a nonsaturable Na+ uptake seen at higher Na+ concentrations up to 20 mM. (c) The rate of Na+ uptake in high Na+ solutions is correlated with the duration of backward swimming and membrane excitation in wild type Paramecium and the mutants fast-2 and paranoiac. (d) Na+ uptake is inhibited at 4 degrees C. From these results, we postulate that Na+ uptake is faster when the membrane is depolarized than when it is at the resting potential level.
Article| May 01 1979
Sodium uptake and membrane excitation in Paramecium.
H G Hansma
Online Issn: 1540-8140
Print Issn: 0021-9525
J Cell Biol (1979) 81 (2): 374–381.
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H G Hansma; Sodium uptake and membrane excitation in Paramecium.. J Cell Biol 1 May 1979; 81 (2): 374–381. doi: https://doi.org/10.1083/jcb.81.2.374
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