A voltage-dependent and pH-sensitive proton current in Rana esculenta oocytes |
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Authors: | S Humez F Fournier P Guilbault |
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Institution: | (1) Laboratoire de Physiologie Cellulaire, SN3, Université des Sciences et Technologies de LILLE, 59655 Villeneuve d'Ascq, Cedex, France |
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Abstract: | Voltage clamp technique was used to study macroscopic ionic currents in Rana esculenta oocytes. Depolarization steps led to the activation of a single type of outward current (I
out) when contaminant potassium and calcium-dependent chloride currents were pharmacologically inhibited. The voltage threshold of I
out activation was 10 mV and this current, which did not inactivate, presented a deactivation the time constant of 73±21 msec (n=26) corresponding to a membrane voltage of –60 mV. Its reversal potential (E
rev) was dependent on the magnitude of the depolarization and also on pulse duration. These changes in E
rev were thought to reflect intracellular ion depletion occurring during activation of the remaining outward current. Furthermore, the activation threshold of I
out was clearly affected by modifications in extracellular and intracellular H+ concentrations. Indeed, intracellular alkalinization (evoked by external application of ammonium chloride) or extracellular acidification induced a rightward shift in the activation threshold while intracellular acidification (evoked by external application of sodium acetate) or extracellular alkalinization shifted this threshold toward a more negative value. Lastly, I
out was dramatically reduced by divalent cations such as Cd2+, Ni2+ or Zn2+ and was strongly decreased by 4 Aminopyridine (4-AP), wellknown H+ current antagonists already described in many cell types. Therefore, it was suggested that the outward current was prominently carried by H+ ions, which may play a key role in the regulation of intracellular pH and subsequent pH dependent processes in Rana oocyte. |
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Keywords: | Rana esculenta oocytes H+ current pH Voltage clamp |
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