Transport of Clonidine at Cultured Epithelial Cells (JEG-3) of the Human Placenta

PURPOSE: This study was performed to characterize the uptake of the antihypertensive drug clonidine at epithelial cells of the human placenta (JEG-3) and its interaction with other cationic drugs. METHODS: Uptake of [3H]clonidine into cells of the human choriocarcinoma cell line JEG-3 was investigated. RESULTS: Uptake of [3H]clonidine into JEG-3 cells reached its maximum on the eighth day after seeding. Uptake of [3H]clonidine was linear for up to 1 min, Na+ independent, but strongly H+ dependent. The uptake rate of clonidine was saturable with an affinity constant (Kt) of 1.1 mM and a Vmax value of 27 nmol x min(-1) x mg(-1) of protein. Several cationic drugs such as clonidine, quinine, quinidine, and diphenhydramine strongly inhibited the [3H]clonidine uptake with Ki values around 1 mM. CONCLUSIONS: Clonidine is transported across the placental epithelium by a carrier mediated process.