A STUDY OF THE MECHANISM OF NEUROTRANSMITTER RELEASE ENHANCEMENT BY AN ENDOGENOUS OUABAIN-LIKE SUBSTANCE.

M. G. BERSIER; V. MIKSZTOWICZ; C. PEÑA; G. RODRÍGUEZ DE LORES ARNAIZ.

Madison, Wisconsin, EE.UU.

Congreso; XXXVI Congreso de la Sociedad Americana de Neuroquímica (ASN); 2005

Sociedad Americana de Neuroquímica (ASN)

A study of the mechanism of neurotransmitter release enhancement by an endogenous ouabain-like substance   Bersier M. G.1, 2, Miksztowicz V.1, Peña C.3 and Rodríguez de Lores Arnaiz G.1,2.  1Inst Biol Cel y Neuroc “Prof E De Robertis”, Fac Med, 2Cát Farmacol and 3IQUIFIB-CONICET, Fac Farm y Bioq, Universidad de Buenos Aires   Inhibition of sodium pump increases neurotransmitter release. In previous work a soluble brain fraction, termed endobain E, was isolated which shares biological properties with ouabain, including the ability to increase neurotransmitter release. Herein we analysed the potential participation of glutamatergic receptors in such effect and to disclose whether this effect is exerted on exocytosis or on reversion of the aminoacid transporter. Endobain E was isolated from a soluble brain fraction of rat cerebral cortex using an anionic exchange HPLC column. Cerebral cortex Synaptosomes were preincubated in HEPES saline buffer with 1 mM D-[3H]Aspartate (15 min at 37ºC), then incubated in the presence of additions (60 seg) at 37º and radioactivity quantified. Antagonists LY 367385 (selective for mGluR1 subtype) and dizocilpine (selective for ionotropic NMDA receptor) failed to alter the release induced by ouabain and endobain E; MPEP (selective for mGluR5 subtype) highly decreased the release induced by ouabain but failed to modify endobain E effect. These results indicate that mGluR5 is only involved in ouabain effect. Aspartate release assayed at 37º, 25º and 18ºC was respectively 370±30, 296±4 and 261±18 (n= 4) with endobain E and 270±17, 192±55 and 132±18 (n= 4-7) with 1 mM ouabain. Since reduction of incubation temperature decreases endobain E and ouabain effect, the mechanism affected is most likely the reversion of the neurotransmitter transporter.