Conductive properties of the rabbit outer medullary collecting duct: outer stripe

Segments of the outer medullary collecting duct were dissected from the outer stripe of the rabbit kidney (OMCDo) and perfused in vitro. The conductive properties of the tubule epithelium and individual cell membranes were determined by means of cable analysis and intracellular voltage-recording microelectrodes. The transepithelial voltage (VT) and resistance (RT) averaged -10.7 +/- 2.5 mV, lumen negative, and 28.5 +/- 2.9 k omega X cm (n = 27), respectively. Two cell types could be defined by their electrophysiological properties. One cell type (n = 7) had a mean basolateral membrane voltage (Vbl) of -30.1 +/- 2.4 mV, a fractional resistance of the apical membrane (fRa = Ra/Ra + Rbl) near unity (0.99 +/- 0.01), and a predominantly Cl(-)-selective basolateral cell membrane. The second cell type (n = 27) had a mean Vbl of -63.7 +/- 2.7 mV, a fRa of 0.81 +/- 0.02, and a predominantly K+-selective basolateral cell membrane. The present study focused on defining the conductive properties of this latter cell type. Amiloride (10(-5) M) and BaCl2 (2 mM) were used as probes of apical cell membrane Na+ and K+ conductive pathways, respectively. Amiloride increased fRa from 0.80 +/- 0.02 to 0.98 +/- 0.01 (n = 12), whereas BaCl2 increased fRa from 0.77 +/- 0.03 to 0.82 +/- 0.03 (n = 9). The conductive properties of the basolateral cell membrane were assessed by ion substitutions of the bath solution. A 10-fold increase in the bath [K+] depolarized Vbl by 34.9 +/- 1.9 mV (n = 16) in less than 1 s, indicating that this membrane was predominantly K+ selective.(ABSTRACT TRUNCATED AT 250 WORDS)