The purpose of this study is to evaluate the impact of genetic variants of OATP 1B3 or MRP 2 on the systemic disposition of endogenously formed CCK-8 and to determine the influence of a single-dose of the transporter inhibitor rifampin (600 mg) on the systemic disposition of endogenously formed CCK-8. Endogenous CCK-8 secretion will be induced by a single-dose standardized liquid mixed meal.