Ionic currents of channels that are permeable to monovalent and divalent cations.
The cation-selective channel from Tetrahymena cilia is permeable to both monovalent and divalent cations. The single channel conductance in mixed solutions of K+ and Ca2+ was determined by the Gibbs-Donnan ratio of K+ and Ca2+, and the binding sites of this channel were considered to be always occupied by two potassium ions or by one calcium ion under the experimental conditions: 5-90 mM K+ and 0.5-35 mM Ca2+ (Oosawa and Kasai, 1988). A two-barrier model for the channel was introduced and the values of Michaelis-Menten constants and maximum currents carried by K+ and Ca2+ were calculated using this model. Single channel current amplitudes and reversal potentials were calculated from these values. The calculated single-channel currents were compared with those obtained experimentally. The calculated reversal potentials were compared with the resting potentials of Tetrahymena measured in various concentrations of extracellular K+ and Ca2+. The method of calculation of ionic currents and reversal potentials presented here is helpful for understanding the properties of the channels permeable to both monovalent and divalent cations.
Oosawa
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Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D002414:Cations, Monovalent; D002923:Cilia / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D013768:Tetrahymena / Q000378:metabolism
D002413:Cations, Divalent; D002414:Cations, Monovalent; D007473:Ion Channels; D011188:Potassium; D002118:Calcium