Properties and regulation of pH-dependent cation channels in the apical membrane of cultured proximal tubule cells.
The established opossum kidney (OK) cell line serves as a model system for ion and substrate transport in the renal proximal tubule. Previous experiments on OK cells revealed a channel-mediated Na+ conductance which is regulated by intracellular pH (pHi). In this study we report on patch clamp experiments determining the properties and pHi dependence of a cation channel located in the apical membrane. This channel is selective for sodium over chloride but discriminates poorly between the monovalent cations Na+,K+,Li+ and Cs+. Its open probability (P(o)) rises at depolarising membrane potentials. Under normal conditions the channel is inactive in the cell-attached patch mode and is activated upon excision. However, after excision the channel usually runs down within 30-90 s which cannot be overcome by either altering the Ca(2+)-concentration (10(-3) mol/l, 10(-6) mol/l, Ca(2+)-free) or adding 1 mmol/l Mg-ATP to the bath solution. In the cell-attached patch mode the channel could be activated by decreasing pHi from pH 7.4 to pH 6.5, by either the ammonium prepulse technique or the nigericin K+ method, in more than 50% of the experiments performed. In the renal proximal tubule such a non-selective cation channel would constitute a functional Na+ channel and might therefore support Na+ reabsorption especially during the intracellular acidification due to hormonal inhibition of the Na+/H+ exchanger.
D000818:Animals; D002460:Cell Line; D018118:Chloride Channels / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008564:Membrane Potentials; D009893:Opossums; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000378:metabolism
D018118:Chloride Channels; D007473:Ion Channels; D015222:Sodium Channels