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N.C. Welch, S. Barnes, M.E. Kelly; Uniformly Distributed Calcium Channels in Retinal Müller Cells Exhibit Currents With a Distinctive Pharmacology . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4138.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Müller cells, the principle glia of the retina, express voltage-gated Ca channels. Our previous work suggested that the pharmacology of Müller cell Ca channel currents was distinct, and here we continue to characterize the pharmacological properties as well as determine the distribution of Ca channels in Müller cells. Methods: Acutely dissociated salamander Müller cells were superfused with 10 mM Ba2+ and 15 mM TEA, with Cs+ included in the pipette, to isolate Ca channel currents during whole-cell patch clamp recordings. Laser scanning confocal microscopy was used to visualize the staining pattern resulting from the fluorescent probe DMBODIPY-DHP, a fluorescent-tagged dihydropyridine, ratioed with the membrane dye FM 143. Results: Whole-cell patch clamp characterization of Ca channel currents in isolated Müller cells used Ba2+ as the charge carrier and have been expressed as mean ± standard deviation. The P/Q-channel blocker, agatoxin, reversibly blocked Ca channel currents by 50% ± 16% (500 nM; n=7) while the N-type channel blocker, Ω-conotoxin GVIA, irreversibly blocked Ca channel currents by 54% ± 33% (1 µM; n=10). The L-type Ca channel blockers, diltiazem and verapamil, reduced Ca channel currents by 39% ± 14% (20 µM; n=9) and 38% ± 22% (50 µM; n=8) respectively. The L-type Ca channel facilitator, BayK, did not enhance Ca channel currents in salamander Müller cells but reduced Ca channel current by 28% ± 13% (1 µM; n=5). The spatial distribution of the surface density of dihydropyridine-sensitive channels was found to be homogeneous over the entire Müller cell. Conclusion: L-type calcium channels in retinal Müller cells are evenly distributed over the cell surface of acutely isolated cells. The distinct pharmacology of these channels makes it difficult to subclassify the channel type(s) according to established pharmacological patterns.
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