Amphetamine (AMPH) elicits its behavioral effects by acting on the dopamine (DA) transporter (DAT) to induce DA efflux into the synaptic cleft. We previously demonstrated that a human DAT construct in which the first 22 amino acids were truncated was not phosphorylated by activation of protein kinase C, in contrast to wild-type (WT) DAT, which was phosphorylated. Nonetheless, in all functions tested to date, which include uptake, inhibitor binding, oligomerization, and redistribution away from the cell surface in response to protein kinase C activation, the truncated DAT was indistinguishable from the full-length WT DAT. Here, however, we show that in HEK-293 cells stably expressing an N-terminal-truncated DAT (del-22 DAT), AMPH-induced DA efflux is reduced by approximately 80%, whether measured by superfusion of a population of cells or by amperometry combined with the patch-clamp technique in the whole cell configuration. We further demonstrate in a full-length DAT construct that simultaneous mutation of the five N-terminal serine residues to alanine (S/A) produces the same phenotype as del-22—normal uptake but dramatically impaired efflux. In contrast, simultaneous mutation of these same five serines to aspartate (S/D) to simulate phosphorylation results in normal AMPH-induced DA efflux and uptake. In the S/A background, the single mutation to Asp of residue 7 or residue 12 restored a significant fraction of WT efflux, whereas mutation to Asp of residues 2, 4, or 13 was without significant effect on efflux. We propose that phosphorylation of one or more serines in the N-terminus of human DAT, most likely Ser7 or Ser12, is essential for AMPH-induced DAT-mediated DA efflux. Quite surprisingly, N-terminal phosphorylation shifts DAT from a “reluctant” state to a “willing” state for AMPH-induced DA efflux, without affecting inward transport. These data raise the therapeutic possibility of interfering selectively with AMPH-induced DA efflux without altering physiological DA uptake.

Evidence suggests that protein kinase C (PKC) and intracellular calcium are important for amphetaminestimulated outward transport of dopamine in rat striatum. In this study, we examined the effect of select PKC isoforms on amphetamine-stimulated dopamine efflux, focusing on Ca 2؉ -dependent forms of PKC. Efflux of endogenous dopamine was measured in superfused rat striatal slices; dopamine was measured by high performance liquid chromatography. The non-selective classical PKC inhibitor Gö 6976 inhibited amphetamine-stimulated dopamine efflux, whereas rottlerin, a specific inhibitor of PKC␦, had no effect. A highly specific PKC␤ inhibitor, LY379196, blocked dopamine efflux that was stimulated by either amphetamine or the PKC activator, 12-O-tetradecanoylphorbol-13-acetate. None of the PKC inhibitors significantly altered [3 H]dopamine uptake. PKC␤ I and PKC␤ II , but not PKC␣ or PKC␥, were coimmunoprecipitated from rat striatal membranes with the dopamine transporter (DAT). Conversely, antisera to PKC␤ I and PKC␤ II but not PKC␣ or PKC␥ were able to co-immunoprecipitate DAT. Amphetamine-stimulated dopamine efflux was significantly enhanced in hDAT-HEK 293 cells transfected with PKC␤ II as compared with hDAT-HEK 293 cells alone, or hDAT-HEK 293 cells transfected with PKC␣ or PKC␤ I . These results suggest that classical PKC␤ II is physically associated with DAT and is important in maintaining the amphetamine-stimulated outward transport of dopamine in rat striatum.

In this study the surface features and the radar backscatter associated with break ing waves generated by a uniform flow past a stationary submerged hydrofoil were examined. The level of energy dissipation due to breaking was varied by changing the foil angle of attack. Time series of surface elevation profiles were obtained for the breaking crest region and the following waves. Radar backscatter (X-band) was also measured for an incidence angle of 45° with the radar looking both upwave and downwave for hh and vv polarizations. These measurements were compared to model predictions of radar backscatter using the surface elevation data as inputs to the model.The breaking crest region exhibited the largest surface disturbances, as measured by the temporal variance of the surface elevation. The maximum in the variance was associated with large low-frequency disturbances in the 'toe' region. Downstreammoving waves appear just ahead of the crest and, due primarily to interaction with the spatially varying current set up by the stationary wave, decrease in amplitude by an order of magnitude as they propagate downstream. These surface disturbances remain at a low level thereafter. A maximum radar cross-section per unit area of about 0.5 was observed near the breaking crest, for both hh and vv polarization in the upwave look direction. The maximum value for the upwave look direction was about twice as large as for the downwave look direction. Downstream of the breaking crest, the radar cross-section decreased rapidly and then leveled off, and an increasing difference between the vv and hh backscatter was observed as the overall backscatter level decreased. Near the second crest, there was a small increase in the height variance and in the radar cross-section.The surface-elevation measurements were used as inputs for a Bragg-scattering model and the expected radar backscatter was calculated. The variations in the observed radar cross-section downstream of the breaking crest are satisfactorily ex plained by the Bragg model when surface-tilt effects are taken into account. However, the backscatter from the breaking crest itself is not accurately predicted since, in this region, the small-scale surface roughness exceed the limits of validity for the Bragg model. In trod u ctionThe use of remote sensing data for observing various dynamical processes in the upper ocean hinges on the relationship between those processes and the remotely sensed variables. For the case of microwave radar remote sensing, the remotely sensed

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