Intracellular microelectrode characterization of the rabbit cortical collecting duct

Abstract

Cortical collecting ducts of the rabbit were perfused in vitro and the intracellular potential (Vbl) was measured with KCl-filled microelectrodes. The ratio of apical to basolateral membrane resistance (Ra/Rbl) was estimated from the voltage divider ratio using cable analysis. In control tubules Vbl averaged -84.0 .+-. 2.5 mV and Ra/Rbl was 0.83 .+-. 0.11. Pretreatment of the rabbits with mineralocorticoid caused Vbl to hyperpolarize to -105.8 .+-. 3.1 mV and Ra/Rbl to decrease slightly to 0.62 .+-. 0.10. A 10-fold increase of the luminal [K+] caused a 40.6 .+-. 3.1 mV depolarization of Vbl in control tubules and a 33.0 .+-. 4.2 mV depolarization in tubules from DOCA[deoxycorticosteroid acetate]-pretreated rabbits. Consistent with the existence of a conductive K+ channel at the apical cell membrane, Ra/Rbl decreased in both groups. This apical K+ channel was not sensitive to amiloride but was blocked by Ba2+. Conductive movement of Na+ across the apical membrane was also apparent in that Ra/Rbl increased with amiloride from 0.61 .+-. 0.10 to 1.45 .+-. 0.28. A 10-fold increase in the bath [K+] caused a 28.6 .+-. 3.8 and a 49.4 .+-. 4.4 mV depolarization of Vbl tubules obtained from control and DOCA-pretreated rabbits, respectively. In both groups, Ra/Rbl increased, suggesting that the basolateral cell membrane may contain a conductive K+ channel. Taken together, the results support a model in which the transepithelial reabsorption of Na+ and the transepithelial secretion of K+ are driven by the Na+-K+-ATPase located in the basolateral cell membrane, with passive movement of these ions occurring through separate conductive pathways in the apical cell membrane.