Characterization of vinpocetine effects on DA and DOPAC release in striatal isolated nerve endings.
The effect of vinpocetine, a nootropic drug with anti-ischemic potential, on the release of DA and its main metabolite, DOPAC, was investigated in striatum isolated nerve endings under resting and depolarized conditions. Vinpocetine does not modify the baseline release of DA or the exocytotic release of DA evoked by high K(+), but inhibits the release of DA evoked by veratridine reversal of the DA transporter. In addition to these results, which confirm the vinpocetine selective blockade of voltage-sensitive presynaptic Na(+) channels (VSSC) previously reported [Neurochem. Res. 24 (1999) 1585], vinpocetine increases DOPAC release either under resting, veratridine or high K(+) depolarized conditions. This latter effect, which does not involve VSSC, was characterized. The parallel determination of the released and retained catecholamine concentrations revealed that vinpocetine increases DOPAC release at the expense of internal DA in a dose-dependent manner (low microM range). In contrast to vinpocetine, the selective MAO-A inhibitor, clorgyline, increases DA and decreases DOPAC formation. The combined action of vinpocetine and clorgyline does not indicate, however, that the activation of MAO is the mechanism responsible for the increase in DOPAC caused by vinpocetine. Reserpine, although more potent and efficient than vinpocetine, qualitatively exerts the same pattern of changes on DA and DOPAC concentrations. It is concluded that, in addition to the inhibition of presynaptic VSSC permeability, which selectively inhibits the transporter-mediated release of all neurotransmitters, vinpocetine increases DOPAC by impairing the vesicular storage of DA. Our results indicate that the cytoplasm extravesicular DA is metabolized by MAO to DOPAC. Most of the DOPAC formed is exported to the extracellular medium.
Trejo
F
F
Instituto de Investigaciones Biomédicas, Apartado Postal 70228, Ciudad 04510, D.F., Universitaria, Mexico.
Nekrassov
V
V
Sitges
M
M
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism*; D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D003010:Clorgyline / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D008297:Male; D008562:Membrane Glycoproteins; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D026901:Membrane Transport Proteins; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D017072:Neostriatum / Q000187:drug effects* / Q000378:metabolism; D009419:Nerve Tissue Proteins; D011188:Potassium / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012110:Reserpine / Q000494:pharmacology; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology; D014748:Vinca Alkaloids / Q000494:pharmacology*
D018759:Adrenergic Uptake Inhibitors; D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008996:Monoamine Oxidase Inhibitors; D009419:Nerve Tissue Proteins; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D014748:Vinca Alkaloids; D015102:3,4-Dihydroxyphenylacetic Acid; C013983:vinpocetine; D014701:Veratridine; D012110:Reserpine; D003010:Clorgyline; D011188:Potassium; D004298:Dopamine