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 (AiCl) with double-barreled Cl-selective microelectrodes. Luminal Cl removed decreased AiCl from 27.4 to 23.7 mM (by 3.7 mM), whereas bath Cl removal decreased AiCl from 27.4 to 12.3 mM (by 13.1 mM). Therefore, the basolateral membrane Cl transport was stronger determinant of AiCl. Basolateral SITS (1 mM) decreased AiCl from 33.9 to 18.7 mM (by 15.2 mM) while 1 mM bath furosemide did not change AiCl. Bath SITS mostly abolished the difference between AiCl 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 AiCl. Removal of luminal Na decreased AiCl from 34.6 to 25.4 mM (by 9.2 mM). After luminal Na removal, subsequent bath Na removal increased AiCl initially, and then decreased to a steady-state AiCl (30.3 mM) which was close to equilibrium Cl distribution across the basolateral membrane (28.4 mM). It is concluded that AiCl 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.