The Effect of the Glucose Substitution Through Succinate on the ERG of the Isolated Superfused Vertebrate Retina

Abstract

Purpose : Succinate is a key intermediate to regenerate chemical energy as GTP/ATP in the tricarboxylic acid cycle. Our objective was to replace the glucose as primary energy source in our perfusion solution for isolated vertebate retinae with succinate and to register the ERG-changes

Methods : In a serum-free nutrient medium (NM) containing (in mM) 120 NaCl, 2 KCl, 0.1 MgCl₂, 0.15 CaCl₂, 1.5 NaH₂PO₄, 13.5 Na₂HPO₄ and 5 glucose, the latest was replaced with 7 mM Succinate (SM, succinate medium). Isolated bovine retinae were mounted in a temperature-controlled recording chamber and initially perfused with NM. Electric field potentials were recorded using Ag/AgCl-electrodes, to obtain the photoreceptor potential after each flash of light. After reaching stable ERG amplitude, SM was administered for 60 minutes. Thereupon, SM was washed out during 60 min reperfusion with the NM. Light intensities of 1 Lux (n=6) and 10 Lux (n=11) were used. To block transsynaptic signal transduction in another series of experiments 1 mM L-aspartate was added during the whole perfusion: 1 Lux (n=4) and 10 Lux (n=6). ERG-changes before, during and after ethambutol-application were calculated and plotted

Results : In all retinae (n=27) SM caused a complete inhibition of the negative a-wave, this effect was reversible after wash-out with NM. However, 11 retinae (40,7%) showed during SM-perfusion a positive ERG amplitude. This effect was observed either in non-aspartate (6 of 17) or aspartate (5 of 10) group, as well as either at 1 Lux (5 of 10) or 10 Lux (6 of 17) light intensities

Conclusions : In 40,7% of retinae by application of SM a novel positive shift in the ERGs was observed, most likely through depolarization of receptor cells, because this effect was also seen in the presence of L-aspartate. Most probably the light perception may have occured through melanopsin-expressing photosensitive retinal ganglion cells (pRGCs), a pathway known to depolarize receptor cells. Alternatively, succinate-receptor mediated interaction with ion channels may also explain the experimental observations

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.