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R. Frazao, R. Heidelberger, D. W. Marshak; Histamine Effects on Dopaminergic Amacrine Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1854. doi: https://doi.org/.
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The experiments were designed to test the hypothesis that dopaminergic amacrine cells are among the targets of histamine released from retinopetal axons in mouse retina.
Dopaminergic amacrine cells were isolated from transgenic mice (C57BL/TH::RFP), expressing red fluorescent protein and plated onto glass coverslips. Cells were loaded for 45 minutes in darkness at 22° C with Fura 2 acetoxymethyl ester (1 µM), and then the coverslips were mounted on the stage of an inverted microscope with epifluorescent illumination. The cells were superfused with HEPES-buffered saline solutions containing histamine, histamine receptor 1 (HR1) antagonists or agonists in a moist oxygen atmosphere at 20 °C. Free intracellular calcium was determined from the ratio of the fluorescence signals excited at the wavelengths 360 and 380 nm. Mean calcium levels were analyzed using paired t-tests.
Superfusion of histamine leads to an increase in mean [Ca++]i of the dopaminergic amacrine cells. The effect was dose-dependent and maximal at 5 µM. Superfusion of 5µM histamine produced an increase in mean [Ca++]i in 79% of the cells analyzed; the increase in mean [Ca++]i was 65%, on average with this dose. The HR1 antagonist pyrilamine blocked the effects of 5 µM histamine when applied at 50 µM. The selective HR1 agonist 2-(3-trifluoromethylphenyl) histamine dihydrogenmaleate applied at 5 µM significantly increased mean [Ca++]i.
The results indicate that the effects of histamine on the dopaminergic cells are mediated by HR1, as predicted in a recent anatomical study of mouse retina.
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