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Homocysteate‐Evoked Release of Acetylcholine from the Rabbit Retina
Author(s) -
Linn David M.,
Massey Stephen C.
Publication year - 1996
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1996.66010153.x
Subject(s) - acetylcholine , kainate receptor , cholinergic , retina , nmda receptor , biophysics , biology , agonist , pharmacology , receptor , chemistry , biochemistry , neuroscience , ampa receptor
The cholinergic amacrine cells of the rabbit retina can be labeled with [ 3 H]choline and the activity of the cholinergic population monitored by following the release of [ 3 H]acetylcholine. It has been proposed that l ‐homocysteate may be the main endogenous transmitter released onto cholinergic amacrine cells by bipolar cells. Therefore, we have examined the effects of the isomers of homocysteate on the release of [ 3 H]acetylcholine. In magnesium‐free medium, d ‐homocysteate was slightly more potent than the l ‐isomer. The addition of magnesium, which blocks responses mediated by NMDA receptors, preferentially reduced but did not eliminate, the response to l ‐homocysteate. 2‐Amino‐7‐phosphonoheptanoate, a potent NMDA antagonist, preferentially blocked l ‐homocysteate evoked responses. 6,7‐Dinitroquinoxaline‐2,3‐dione, a potent kainate antagonist, preferentially blocked d ‐homocysteate‐evoked responses. Therefore, in the rabbit retina, l ‐homocysteate is an NMDA‐preferring agonist, whereas d ‐homocysteate is a kainate‐preferring agonist. In addition, we found that l ‐homocysteate can activate the physiologically activated kainate receptor but only when used in millimolar concentrations and under conditions that minimize NMDA‐receptor activation. However, the low potency of l ‐homocysteate combined with low affinity for the glutamate transporter, lack of immunocytochemical localization in bipolar cells, and low retinal content place serious limitations on the role of l ‐homocysteate at the bipolar‐to‐cholinergic amacrine cell synapse.