P-glycoprotein does not actively transport nicotine and cotinine

The ABCB1 gene transporter P-glycoprotein (P-gp) exists in the blood-brain barrier (BBB) and placenta and limits many drugs passing through the BBB and placenta. Several recent studies have raised confounding results regarding the roles of P-gp in nicotine disposition. To ascertain this question, we examined the effects of nicotine and its major oxidative metabolite, cotinine, on ATPase activity using P-gp containing membranes, in which nicotine and cotinine-stimulated inorganic Pi was used as a marker of the binding affinity of nicotine and cotinine to P-gp. At concentrations ranging from 5 to 1000 microm, both nicotine and cotinine produced modest stimulative effects on ATPase activity in the P-gp containing membrane. The Clint values of nicotine and cotinine were 0.01 and 0.007 minute(-1) x 10(-3), respectively. The positive control, verapamil, at concentrations ranging from 1 to 100 microm, created apparent stimulative effects on ATPase activity, with a Clint value of 1.7 minute(-1) x 10(-3), consistent with previously reported results. The results of the current study suggest that nicotine and cotinine were not actively transported by P-gp out of the cells. The observed carrier-mediated nicotine transport in various cell lines may be mediated by other transporter proteins but not P-gp.