Transport of tetraethylammonium by rabbit renal brush-border and basolateral membrane vesicles

Brush-border and basolateral membrane vesicles (BBMV and BLMV, respectively) from rabbit renal cortex were used to study transport of the organic cation, tetraethylammonium (TEA). Outwardly directed proton gradients stimulated uptake of TEA into BBMV and supported concentrative accumulation. Furthermore, an inwardly directed H⁺ gradient accelerated TEA efflux from BBMV. These data suggest that TEA transport in BBMV involved exchange with H⁺. The J(max) and K(t) for TEA transport into BBMV under pH equilibrium conditions (pH 7.5) were 2.1 nmol·mg^-1·min^-1 and 0.15 mM, respectively. Under pH gradient conditions (6.0(in):7.5(out)), J(max) increased by 270% with no effect on K(t). Uptake of TEA into BBMV was stimulated by an inside-positive electrical potential difference (PD), although exchange of TEA for H⁺ appeared to be one for one. In BLMV, H⁺ gradients had little effect on TEA uptake and were incapable of supporting concentrative transport. The J(max) and K(t) for TEA transport in BLMV were 0.33 nmol·mg^-1·min^-1 and 0.37 mM, respectively. Inside-negative PDs stimulated this uptake, suggesting that it involved an electrically conductive pathway. TEA transport in BBMV and BLMV was inhibited by amiloride and cimetidine, although p-aminohippuric acid was without effect. Thus, secretion of TEA involves carrier-mediated transport steps at both the luminal and peritubular membranes, although an active step is not evident in isolated BLMV.