Abstract
Purpose :
Regarding the functional role of horizontal cells (HCs) in the retina, three mechanisms have been extensively studied at the cone pedicle, including GABA mediated feedback, hemichannel dependent current modulation, and pH effect on calcium current. But, it is yet unclear the functional contribution of HCs in the rod visual pathway. This study tested the hypothesis that HCs may modulate the output signals at the rod synaptic terminal by combining at least two of the three previously mentioned mechanisms.
Methods :
Adult, healthy, mouse strain of wild-type C57BL/6J was used for electroretinogram (ERG) and immunohistochemical (IHC) labeling. The physiological study was carried out on dark-adapted (> 12 hours) animals in vivo by recording binocular responses of the rod-mediated ERG signals in response to low intensity full-field light stimuli (≤ 0.01 cd.s/m2) after the right eye of each animal was intravitreally injected with 1 μL of a solution containing GABA (100 mM), Glutamate (100 mM), Bicuculline (10 mM), DNQX (30 mM), APB (25 mM), HEPES (25 mM), TPMPA (5 mM) or the combination of those compounds. Meanwhile, the left eye was injected with 1 μL of PBS solution. We also performed a study about the localization and colocalization of molecular proteins in the retina, including calbindin, GABA, and anion exchanger 3 (AE3).
Results :
The rod response was abolished by APB and relevantly diminished by TPMPA. Experimental stimulation of HCs membrane receptors by GABA and glutamate produced a significant increase in the rod response (p < 0.05), the injection of its antagonists (Bicuculline and DNQX) produced a significant decrease in the rod response (p < 0.01). The rod response showed a statistically significant roll-off decrease since the acid-base condition of the triadic synaptic cleft is justified by intraocular injection of HEPES, whose pH was adjusted to 7.2, 7.4, and 7.6. In the IHC study, it was found that calbindin was localized in the outer plexiform layer, and both GABA and AE3 colocalized with calbindin.
Conclusions :
HCs modulate the transmission of light signaling received in the rod visual pathway in the first synapse by strictly sticking to the pH regulation in the synaptic cleft, whose pH condition is determined by the flux of HCO3-, which is controlled by GABAergic HCs′ membrane receptors.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.