Na+ selective channels in the apical membrane of rabbit late proximal tubules (pars recta)
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- Gögelein, H. & Greger, R. Pflugers Arch. (1986) 406: 198. doi:10.1007/BF00586683
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Using the patch-clamp technique, Na+ selective channels were observed in the luminal membrane of rabbit straight proximal tubule segments. In the cell-attached configuration (NaCl-Ringers in pipette and bath) influx of Na+ ions from the pipette into the cell through fluctuating channels was observed was observed. The current-voltage curve of these Na+ channels yielded a zero-current potential of 84.3±30.9 mV (n=10), reflecting the electrochemical driving force for Na+ influx under resting conditions. The single channel conductance was 12.0±2.1 pS (n=13). In inside-out oriented cell-excised patches the single channel conductance was not significantly different with NaCl-Ringers on both sides. At clamp potentials ranging from +50 mV to −50 mV the single channel current was ohmic and channel kinetics were independent of the voltage. With KCl-Ringers on the bath side (corresponding to cell interior), the zero current potential was 62±19 mV (n=4), indicating a high selectivity of Na+ over K+ ions. Addition of 10−5 mol/l amiloride to the bathing solution decreased the mean channel open time slightly. This effect was more pronounced with 10−4 mol/l amiloride, whereas the single channel conductance was unaffected by the diuretic. 10−3 mol/l amiloride caused a complete block of the channel. It is concluded that amiloride sensitive Na+ channels, with similar properties to those observed in tight epithelia, contribute to Na+ reabsorbtion in the straight portion of proximal tubules.