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Vol. 296, Issue 3, 931-938, March 2001
Department of Pharmacology and Neuroscience Program, University of
Colorado Health Sciences Center, Denver, Colorado
The dopamine (DA) transporter (DAT) regulates dopaminergic synaptic
transmission by controlling extracellular levels of DA. Thus,
understanding signaling mechanisms that alter DAT function is critical
for understanding dopaminergic neurotransmission. We have expressed the
human DAT (hDAT) in Xenopus laevis oocytes to test the
hypothesis that protein tyrosine kinases (PTKs) acutely regulate DAT
function by altering cell surface expression of the transporter. Using
a relatively high concentration of DA (10 µM), we found that several
PTK inhibitors, namely, genistein, lavendustin A, and tyrphostin 25 (10 µM), decreased DA uptake velocity by 58, 41, and 30% of control,
respectively. Furthermore, genistein potently inhibited DA uptake with
a Ki = 68 nM. Kinetic analysis confirmed that genistein decreased the Vmax
of the DAT, with no change in Km. The
effects of PTK inhibition on hDAT-associated currents were also
measured. All three PTK inhibitors attenuated substrate
transport-associated currents to similar extents as DA uptake. In
contrast, the potent Src inhibitor
4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) did not significantly inhibit either DA uptake or
transport-associated currents. PTK inhibitors decreased hDAT-associated
leak currents, however in a more variable manner than for uptake and
transport-associated currents. Genistein also decreased cell surface
binding of [3H]WIN 35,428 to hDAT by 48% of control.
Together, these data provide several lines of evidence suggesting that
PTK inhibition rapidly reduces hDAT activity via redistribution of the
transporter away from the cell surface. Thus, PTKs likely represent
another component of cellular signaling cascades that acutely regulate
neurotransmitter transporters.
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