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Novel properties of the depolarization-induced endogenous sodium conductance in the Xenopus laevis oocyte

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Rettinger,  Jürgen
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Rettinger, J. (1999). Novel properties of the depolarization-induced endogenous sodium conductance in the Xenopus laevis oocyte. Pflügers Archiv: European Journal of Physiology, 437, 917-924. doi:10.1007/s004240050863.


Cite as: https://hdl.handle.net/21.11116/0000-0007-1DAF-5
Abstract
It has been shown by means of the two-microelectrode voltage-clamp technique that in membranes of Xenopus laevis oocytes a Na+-selective permeability can be activated by long-lasting or repetitive depolarization (R.T. Kado and C. Baud, Journal of Physiology, Paris, 77:1113–1117, 1981). In this study the permeability in inside-out giant membrane patches with diameters of 20–30 µm was analysed. Once induced, the Na+ permeability has a voltage-dependent open probability that increases with positive potentials and half-maximally activates at about 0 mV. Sudden changes of membrane potential elicit transient currents with strongly voltage-dependent time constants of from less than 1 ms at –150 mV to several hundreds of milliseconds at positive potentials. In contrast to the on-cell configuration, the permeability ceases completely within a few minutes in the cell-free inside-out configuration. This rundown can be prevented by including MgATP, but not Mg2+ or ATP alone, in the intracellular solution. Intracellular Mg2+ ions, in addition to being a co-factor for ATP in the activation process, decrease the permeability in a dose-dependent manner. Steady-state fluctuation analysis gave no evidence that an increased noise level is caused by open–close kinetics of an ion channel, suggesting that the single-channel conductance is below 1 pS if a channel-like structure is the origin of the endogenous Na+ permeability.