BIOGENIC-AMINE FLUX MEDIATED BY CLONED TRANSPORTERS STABLY EXPRESSED IN CULTURED-CELL LINES - AMPHETAMINE SPECIFICITY FOR INHIBITION AND EFFLUX

LLC-PK1 cells have been stably transfected with cDNAs encoding the hum an norepinephrine transporter (NET), rat dopamine transporter (DAT), a nd rat serotonin transporter. Using these cell lines, the specificity of each transporter toward agents that inhibit substrate influx and st imulate substrate efflux across the plasma membrane was examined. With 1-methyl-4-phenylpyridinium as a substrate for DAT and NET and seroto nin as a substrate for the serotonin transporter, each transporter dem onstrated a distinct pattern of inhibition by a panel of amphetamine d erivatives and analogs, including amphetamine, methamphetamine (also k nown as ''ecstasy''), p-chloroamphetamine, 3,4-methylenedioxymethamphe tamine, methylphenidate (ritalin), and 5-methoxy-6-methyl-2-aminoindan . For each cell line expressing a single biogenic amine transporter, e fflux of the accumulated substrate was stimulated by amphetamine deriv atives, and this efflux was blocked by mazindol, an inhibitor of all t hree transporters. Of the amphetamine derivatives tested, some caused efflux at concentrations similar to those that inhibited transport. Ot her derivatives were much less effective at stimulating efflux than at inhibiting uptake. Methylphenidate caused little or no efflux, althou gh it blocked uptake mediated by both NET and DAT. Other inhibitors of transport, such as cocaine, mazindol, citalopram, and nisoxetine, fai led to stimulate efflux from these cells at concentrations that inhibi ted influx. The results suggest that potency toward individual plasma membrane biogenic amine transporters and the ability to release accumu lated amine substrates are independent properties of each amphetamine derivative.