Stimulation of Noradrenaline Release by T-588, a Cognitive Enhancer, in PC12 Cells

Previously, we reported that (R)-(-)-1-(benzo[b]thiophen-5-yl)-2-[2-(N,N- diethylamino)ethoxy] ethanol hydrochloride (T-588), a novel putative cognitive enhancer, stimulated noradrenaline (NA) release from rat cerebral cortical slices. In this study, we investigated the effects of T-588 compared to other secretagogues on NA release from PC12 cells. Addition of as little as 10 microM T-588 stimulated [3H]NA release in a dose-dependent and an extracellular Ca(2+)-independent manner from PC12 cells. Ten micromolar ionomycin-, 300 microM adenosine-5'-O-(gamma-thiotriphosphate)- and 10 microM forskolin-induced extracellular Ca(2+)-dependent [3H]-NA release was further enhanced by 30 microM T-588. Cytosolic synaptophysin and 25-kDa synaptosome-associated protein immunoreactivity was increased by addition of T-588 in a dose-dependent manner. Interestingly, increases in synaptic vesicle-related proteins triggered by T-588 had a 4-min lag time and were completely dependent on extracellular CaCl2. These findings suggest that T-588 stimulates NA release from PC12 cells in a Ca(2+)-independent manner. T-588 also induced the translocation of synaptic vesicles in a Ca(2+)-dependent manner.