RT Journal Article
SR Electronic
T1 Calcium-Dependent Inhibition of Synaptosomal Serotonin Transport by the  α<sub>2</sub>-Adrenoceptor Agonist  5-Bromo-<em>N</em>-[4,5-dihydro-1<em>H</em>-imidazol-2-yl]-6-quinoxalinamine  (UK14304)
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 956
OP 965
DO 10.1124/jpet.102.047134
VO 305
IS 3
A1 Twum-Ampofo Ansah
A1 Sammanda Ramamoorthy
A1 Sylvia Montañez
A1 Lynette C. Daws
A1 Randy D. Blakely
YR 2003
UL http://jpet.aspetjournals.org/content/305/3/956.abstract
AB Termination of serotonergic transmission is the function of the plasma membrane 5-hydroxytryptamine (serotonin, 5-HT) transporter (SERT), which is also a high-affinity target in vivo for antidepressants, amphetamines, and cocaine. Studies show that SERT is regulated by protein kinase- and phosphataselinked pathways. In contrast, receptor-linked modulation of SERT is only minimally defined. Because noradrenergic stimulation is reported to influence 5-HT release, we explored possible presynaptic adrenoceptor-mediated regulation of SERT. In mouse forebrain synaptosomes, α2-adrenoceptor agonists, particularly 5-bromo-N-[4,5-dihydro-1H-imidazol-2-yl]-6-quinoxalinamine (UK14304), triggered a concentration- and time-dependent decrease in 5-HT transport. In contrast, 5-HT uptake was unaffected by pharmacological α1-adrenoceptor activation. Kinetically, UK14304 significantly decreased the apparent substrate affinity, Km without altering transport capacity, Vmax. At concentrations of UK14304 supporting maximal inhibition of SERT in synaptosomes, no effect on SERT in transfected cells was observed, suggesting that UK14304 acts indirectly to reduce SERT activity. The effect of UK14304 on 5-HT uptake was not shared by other Na+ and Cl—-dependent transporters. UK14304-mediated inhibition of SERT function was yohimbine-sensitive, as was inhibition triggered by norepinephrine, and was abolished in the absence of added Ca2+. Moreover, UK14304 effects were attenuated by voltage-sensitive Ca2+ channel antagonists, consistent with a role for Ca2+ in UK14304 effects. In agreement with altered 5-HT transport activity in vitro, in vivo chronoamperometry studies revealed that UK14304 significantly prolonged 5-HT clearance. Our findings suggest that UK14304 modulates SERT function in vitro and in vivo via signaling pathways, possibly supported by an influx of Ca2+ through voltage-sensitive Ca2+ channels. The American Society for Pharmacology and Experimental Therapeutics