Shoichi Asano (1), Toshio Matsuda (1), Yukiko Nakasu (1), Sadaaki Maeda (2), Hiroyuki Nogi (1) and Akemichi Baba (1,*)
(1) Department of Pharmacology, Faculty of Pharmaceutical Sciences, (2)
Department of Pharmacology, Faculty of Dentistry, Osaka University, Osaka
565, Japan
(*) To whom correspondence should be addressed.
Abstract: [3H]Serotonin (5-HT) uptake by synaptosomes of rat
brain was dose-dependently inhibited by nitric oxide (NO) donors such as
sodium nitroprusside (SNP), 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine,
3-morpholinosydnonimine and S-nitroso-L-cysteine (NO-CYS). The inhibitory
effect was blocked by reduced hemoglobin. The effect was not mimicked by
ferrocyanide and ferricyanide. 8-Bromoguanosine 3',5'-cyclic monophosphate
(8-bromo cGMP) did not affect [3H]5-HT uptake into rat cortical synaptosomes.
The reduced activity of [3H]5-HT uptake into the cortical synaptosomes pretreated
with NO-CYS was partially reversed by washing the preparation after the
treatment. Kinetic analysis showed that NO-CYS (100 microM) decreased the
Vmax value without any change in the Km value. NO-CYS did not affect the
specific binding of [3H]paroxetine, a ligand that binds to the 5-HT transporter,
in membranes. NO-CYS and SNP, like iodoacetic acid and sodium cyanide, decreased
the ATP content in cortical synaptosomes, but the effect on ATP content
was not related to that on [3H]5-HT uptake. These findings suggest that
NO inhibits reversibly [3H]5-HT uptake into rat brain synaptosomes without
affecting the recognition site of the 5-HT transporter in a cGMP-independent
manner, and the observed effect is not due to its metabolic effect.
Keywords: Serotonin (5-HT), Uptake, Nitric oxide (NO), S-Nitroso-L-cysteine
(NO-CYS), Synaptosome