Characterization of Prostaglandin E₁ Transport in Rat Renal Brush-border Membrane

Abstract

  Transport of prostaglandin E₁ (PGE₁) was investigated in rat renal brush-border membrane vesicles. The uptake of [³H]PGE₁ was sensitive to osmosis and temperature. This uptake was saturable and mediated by high-affinity (K_m=2.1 μM)/low-capacity (V_max=17.4 pmol/mg protein/30 sec) and low-affinity (K_m=526.5 μM)/high-capacity (V_max=1032.5 pmol/mg protein/30 sec) transport systems. [³H]PGE₁ uptake was Na⁺-independent and inhibited by various eicosanoids including PGE₂ and PGF_2α. Bromcresol green and sulfobromophthalein, potent inhibitors of prostaglandin transporter (PGT), significantly decreased [³H]PGE₁ uptake. Uptake was also inhibited by indomethacin and probenecid, which reportedly have little effect on PGT. Benzylpenicillin and taurocholate decreased the uptake of [³H]PGE₁. Like p-[¹⁴C]aminohippurate (PAH) uptake by vesicles, the uptake of [³H]PGE₁ was stimulated by an inside-positive membrane potential, created by applying an inward K⁺ gradient and valinomycin. However, the uptake of [³H]PGE₁ was not inhibited by PAH, suggesting that PAH and PGE₁ are transported by separate transport systems. [³H]PGE₁ uptake was not stimulated by outwardly directed gradients of Cl^- nor unlabeled PGE₁, indicating that an anion exchanger may not be involved in PGE₁ transport. These findings suggest that the transport of PGE₁ in rat renal brush-border membrane is mediated by specific transport system(s), at least in part, by a potential-sensitive transport system.