Origin of positive trans epithelial potential difference in early distal segments of rat kidney

Allen, Glen G.; Barratt, Lindsay J.
April 1985
Kidney International;Apr1985, Vol. 27 Issue 4, p622
Academic Journal
Previous studies from our laboratory indicate that early distal segments of the rat kidney have a positive transepithelial potential difference (PD). The present study investigates the origin of the positive PD. PDS were measured in early distal segments using a technique which allowed simultaneous microperfusion and PD measurement through a single pipette (3 to 6 μm O.D). Microperfusion with artificial plasma ultrafiltrate resulted in a significantly negative mean PD of -4.9 ± 0.7 mV (N = 17), in contrast to a positive free-flow PD of +5.7 ± 1.1 mV (N = 174) (P < 0.001). Addition of amiloride 10-4 M to plasma utirafiltrate changed the PD to +1.7 ± 0.2 mV (N = 25, P < 0.001). In contrast, furosemide 10-4 M had no effect on the perfusion PD. Removal of sodium from the luminal perfusate abolished any effect of amiloride on the perfusion PD, Perfusion with artificial early distal fluid yielded a positive PD of +4.2 ± 0.2 mV (N = 19). Amiloride increased this PD to +8.3 ± 0.7 mV (N = 21, P < 0.001). Subsequent experiments in which the sodium and potassium concentrations of the perfusates were varied indicated that concentration gradients for these ions across the early distal tubule could generate substantial diffusion PDs and that potassium was much more permeant than sodium. In conclusion, (1) the positive PD occurring in the early distal tubule under free-flow conditions is probably generated by inward diffusion of potassium and sodium ions down respective concentration gradients: (2) this positive diffusion PD is of sufficient magnitude to mask the contribution of a component of active electrogenic sodium reabsorption in this segment: (3) active sodium transport in the early distal tubule is inhibited by amiloride but unaffected by furosemide: (4) the positive PD in the rat early distal tubule appears to be generated by mechanisms quite different from those described for the thick ascending limb of the rabbit kidney.


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