Intracellular electrical potentials in the rabbit collecting ducts perfused in vitro

Cortical collecting ducts (CCD) and inner stripe of outer medullary collecting ducts (OMCD) of the rabbit were perfused in vitro and the electrical potential was measured with 0.5 M KCl-filled conventional microelectrodes. In CCD, the transepithelial potential (Vte) was -1.9 +/- 0.5 (S.E.) mV and the intracellular potential (Vb) was -74.5 +/- 1.3 mV, while in OMCD, Vte was +2.0 +/- 0.4 mV and Vb was -24.6 +/- 1.0 mV. Acute reduction of peritubular HCO3- concentration from 25 to 5 mM (from pH 7.4 to 6.9) decreased Vb slowly but markedly from -26.3 +/- 1.8 to -18.9 +/- 1.6 mV (p less than 0.001) in OMCD, while it depolarized Vb slightly in CCD (from -75.6 +/- 1.9 to -74.3 +/- 2.1 mV, P less than 0.05). Acute peritubular pH reduction with HCO3- -free HEPES-buffered solution also depolarized Vb of OMCD from -24.7 +/- 2.1 to -15.9 +/- 1.6 mV (p less than 0.001). Although the mechanism(s) of Vb depolarization in OMCD is unclear at the moment, this depolarization suggests that OMCD is responsive to peritubular pH alterations. The results of this study provide the evidence that the collecting duct is heterogeneous in Vb values and its response to the peritubular pH change.