Uptake and release of meta-tyramine, para-tyramine, and dopamine in rat striatal slices

The uptakes of high-affinity concentrations (10(-8)M) of meta-tyramine (m-TA), para-tyramine (p-TA), and dopamine (DA) into rat striatal slices have been shown to be inhibited by DNP and ouabain. We now demonstrate that cocaine (5 x 10(-6)M) and low concentrations of sodium ion (26 x 10(-3)M) also reduced these uptakes. The spontaneous efflux and the release [induced by an elevated concentration of potassium ion (5 x 10(-2)M)] of each of the previously accumulated amines were studied in the presence and absence of added calcium ions. The spontaneous efflux of each amine (especially the tyramines) was enhanced by the absence of calcium ions. Part of this enhancement seemed to be due to an inhibition of a calcium-dependent reuptake. The elevated concentration of potassium ion proved to be an effective releaser of each amine; and for DA, such release was decreased by the removal of calcium. For m- and p-TA, however, the removal of calcium either did not reduce or completely abolished the releases depending upon the duration of the calcium removal. The significance of these findings is discussed.