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  • Title: Characterization of apical and basolateral membrane conductances of rat inner medullary collecting duct.
    Author: Stanton BA.
    Journal: Am J Physiol; 1989 May; 256(5 Pt 2):F862-8. PubMed ID: 2719119.
    Abstract:
    Initial segments of the inner medullary collecting duct of the rat were perfused in vitro, and the electrophysiological properties of the apical and basolateral membranes were examined with KCl-filled microelectrodes. The fractional resistance of the apical membrane (FRa = Ra/Ra + Rbl) and the transepithelial resistance (RT) were estimated by cable analysis. In control tubules the transepithelial voltage (VT) averaged -2.2 mV, and the voltage across the basolateral membrane (Vbl) averaged -51.1 mV. RT was 11.9 k omega.cm (72.8 omega.cm2), and FRa was 0.94. Pretreatment of the rats with deoxycorticosterone (DOC)-pivalate for 7-10 days did not alter these electrophysiological properties. In control tubules, amiloride in the lumen (10(-5) M) changed VT from -3.0 to +1.4 mV and increased Vbl from -49.4 to -53.8 mV, RT from 12.5 to 13.6 k omega.cm, and FRa from 0.92 to 0.98. Thus the apical membrane is conductive to Na+. An increase of the bath K+ concentration from 4 to 15 mM caused an 18.8 mV depolarization of Vbl: barium in the bath also depolarized Vbl. A fivefold decrease in the [HCO3-] in the bath depolarized Vbl by 13.1 mV. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) blocked this depolarization. Thus the basolateral membrane is conductive to K+ and HCO3-. Experiments with ouabain revealed a Na+-K+-ATPase in the basolateral membrane. Taken together, the results support a model in which electrogenic Na+ absorption is driven by the Na+-K+-ATPase in the basolateral membrane, with passive movement of Na+ occurring through an amiloride-sensitive conductive pathway in the apical membrane.
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