INTRACELLULAR CL- ACTIVITY IN RABBIT PROXIMAL CONVOLUTED TUBULE PERFUSED IN-VITRO - REGULATION BY SODIUM AND EFFECTS OF ANION TRANSPORT INHIBITORS

The mechanism of Cl transport was studied in rabbit proximal convoluted tubules (PCT) perfused in vitro by measuring intracellular Cl activity (A(i Cl)) with double-barreled Cl-selective microelectrodes. Luminal Cl removal decreased A(i Cl) from 27.4 to 23.7 mM (by 3.7 mM), whereas bath Cl removal decreased A(i Cl) from 25.4 to 12.3 mM (by 13.1 mm). Therefore, the basolateral membrane Cl transport was stronger determinant of A(i Cl). Basolateral SITS (I mM) decreased A(i Cl), from 33.9 to 18.7 mM (by 15.2 mM) while 1 mM bath furosemide did not change A(i Cl). Bath SITS mostly abolished the difference between A(i Cl) change by luminal Cl removal and that by bath Cl removal. On the other hand, DIDS (0.5 mm) or furosemide (0.1 mM) in the lumen barely changed A(i Cl). Removal of luminal Na decreased A(i Cl) from 34.6 to 25.4 mM (by 9.2 mM). After luminal Na removal, subsequent bath Na removal increased A(i Cl), initially, and then decreased to a steady-state A(i Cl) (30.3 mM) which was close to equilibrium Cl distribution across the basolateral membrane (28.4 mM). It is concluded that A(i Cl) of PCT is regulated more strongly by basolateral Cl transport, and that Na-dependent Cl transport mechanisms are present at each cell membrane of PCT epithelium.