Tetraethylammonium transport by isolated perfused snake renal tubules

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Abstract
Tetraethylammonium (TEA) transport was studied in isolated perfused snake (Thamnophis spp.) proximal renal tubules. Unidirectional lumen-to-bath .**GRAPHIC**. and bath-to-lumen .**GRAPHIC**. fluxes exhibited saturation kinetics, but .**GRAPHIC**. also exhibited an apparent diffusive component and .**GRAPHIC**. did not. .**GRAPHIC**. exceeded .**GRAPHIC**. at all concentrations studied, resulting in net TEA secretion. Transport into cells across both luminal and peritubular membranes was apparently against an electrochemical gradient and was inhibited by cyanide. Km for .**GRAPHIC**. (5.9 .mu.M) was about 1/3rd Km for .**GRAPHIC**. (19.9 .mu.M), indicating greater affinity of the luminal transporter for TEA; but Vmax for .**GRAPHIC**. (153 fmol .cntdot. min-1 .cntdot. mm-1) was about 6 times Vmax for .**GRAPHIC**. (27 fmol .cntdot. min-1 .cntdot. mm-1), indicating a greater capacity of the peritubular transporter for TEA, which could account for net TEA secretion. .**GRAPHIC**. was inhibited by N-methylnicotinamide (NMN) in the bath, but .**GRAPHIC**. was inhibited initially and then apparently transstimulated by NMN in the lumen, indicating possible countertransport. .**GRAPHIC**. but not .**GRAPHIC**. was significantly reduced by replacement of Na with sucrose, indicating possible Na dependency of the luminal transporter. All data indicate active (either primary or secondary) TEA transport at both luminal and peritubular membranes but net transepithelial transport in the bath-to-lumen direction.