Glutamate receptors in the retina: Their modulation by polyamines [Receptores de glutamato en la retina: Su regulación por poliaminas]
Por:
Calderón F., López-Colomé A.M.
Publicada:
1 ene 2000
Resumen:
Endogenous polyamines, as spermine and spermidine, are synthesized from ornithine via ornithine decarboxylase (ODC), and putrescine thus formed enters a closed synthetic loop in which putrescine, spermidine, and spermine are essentially interconvertible and extremely long-lived. Polyamine concentration and metabolism as well as ODC are high in developing tissue; an increase in these parameters is observed in nervous tissue upon activation of voltage- or receptor-operated calcium channels. Inhibition of polyamine synthesis by the irreversible ornithine decarboxylase inhibitor difluoromethylornithine abolishes calcium entry through various receptor-linked or voltage-regulated calcium channels, which can be restored by the addition of putrescine. This property would place such compounds in a powerful position in relation to the control of cerebral neurotranssmission. Recently, spermidine and spermine have been postulated as neuromodulators or neurotransmitters. These molecules interact with the N-methyl-D-aspartate (NMDA) type of glutamate receptor, probably as neuromodulators, evoking distinct effects which indicates the presence of more than one polyamine binding-site on this receptor-channel. Two of these effects are related to the coagonist glycine. In the presence of a saturating concentration of glycine, spermine and spermidine induce an increase in whole-cell current, possibly due to an increase in the frequency of NMDA receptor-channel opening; in the presence of subsaturating concentrations of glycine, spermine and spermidine increase the affinity of the NMDA receptors for this amino acid. Little is known regarding the factors that control polyamine activity in the brain, in rat striatum, spermine and spermidine are selectively released by NMDA-receptor activation and by sodium-pump inhibition with ouabain. [3H]spermidine can also be released from brain slices by depolarizing stimuli in a Ca2+-dependent manner. In the retina, excitatory transmission from photoreceptors to bipolar cells, as well as from bipolar cells to ganglion cells uses glutamate as a transmitter, acting through ionotropic (NMDA, AMPA/KA) as well as metabotropic receptors. Recent results demonstrate that tlie eftects evoked by speimine on NMDA receptors from plexiform layers of chick retina, differ from those in o
Filiaciones:
Calderón F.:
Instituto de Fisiologia Celular, Depto. de Neurociencias, Apdo. Postal 70-253, 04510 México D.F., Mexico
López-Colomé A.M.:
Instituto de Fisiologia Celular, Depto. de Neurociencias, Apdo. Postal 70-253, 04510 México D.F., Mexico
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