| 20002018 |
Siapich SA, Banat M, Albanna W, Hescheler J, Luke M, Schneider T: Antagonists of ionotropic gamma-aminobutyric acid receptors impair the NiCl2-mediated stimulation of the electroretinogram b-wave amplitude from the isolated superfused vertebrate retina. Acta Ophthalmol. 2009 Nov;87(8):854-65.
PURPOSE: NiCl (2) (15 microM) stimulates the electroretinogram (ERG) b-wave amplitude of vertebrate retina up to 1.5-fold through its blocking of E/R-type voltage-gated Ca (2+) channels. Assuming that such an increase is mediated by blocking the release of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) via ionotropic GABA receptors, we tested the effect of both GABA itself and GABA-receptor antagonists such as (-) bicuculline (1.51-fold increase) and (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA; 1.46-fold increase) on the b-wave amplitude. METHODS: Recording of the transretinal potentials from the isolated bovine retina. RESULTS: GABA (100 microM) reduced the b-wave amplitude only when NiCl (2) (15 microM) was applied first. Each antagonist applied on its own stimulated the b-wave amplitude only partially: subsequent NiCl (2) superfusion caused a small but additional increase, leading to a 1.69- and a 1.88-fold total increase of the amplitude by Ni (2+) plus (-) bicuculline or Ni (2+) plus TPMPA, respectively. Only the application of both antagonists in combination, before superfusing low NiCl (2) (15 microM), completely prevented subsequent stimulation by NiCl (2) with a similar 1.90-fold total increase of b-wave amplitude. Those retina segments that did not respond to NiCl (2) could not be stimulated by (-) bicuculline and vice versa. CONCLUSION: The stimulatory effect of NiCl (2) on the ERG b-wave amplitude is mainly, but not only, mediated by a NiCl (2)-sensitive, Ca (v) 2.3-triggered GABA release acting through ionotropic GABA-A and GABA-C receptors. |
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