ENDOTHELIN RECEPTORS IN SYNAPSES OF THE OUTER PLEXIFORM LAYER

VANESA TORBIDONI, MARÍA IRIBARNE, ANGELA M. SUBURO

Nashville, Tennessee.

Simposio; Neuroprotective Strategies in Degenerative Eye Disease; 2006

We described presence of endothelin receptors, ET-A and ET-B, in the outer plexiform layer (OPL) of mouse retina. After light-induced degeneration of photoreceptors, endothelinergic structures disappear from the OPL. Besides, blocking ET receptors we reduced photoreceptor apoptosis induced by light. Our purposes were to identify cells in OPL bearing ET receptors and to study the stress activated protein kinase/Jun N-terminal kinase phosphorilated (Phospho-SAPK/JNK) after 1 day of continuous illumination. BALB-c mice were maintained under 12hours light (bellows 60 lux)/ 12hours dark or under 1500 lux during 1 day. Retinal sections were double labeled with ET-A or ET-B sera and with antibodies against the synaptic protein SV2 (marker of photoreceptor terminals) or a phosphorylated epitope of the 200kd neurofilament (NF-200, marker for horizontals) or Protein kinase C (PKC, marker for rod bipolar cells). We studied Phospho-SAPK/JNK by immunohistochemistry and western blot. In animals under basal illumination conditions, ET-A immunofluorescence demonstrated a layer of varicosities in OPL. Photoreceptor processes labeled with SV-2 presented similar appearance. However there was not co-localization between these markers. Neither NF-200 nor PKC colocalized with ET-A   Vanesa Torbidoni, Página 2, 28/07/2008 Young Investigator Travel Award Application   terminals of OPL. ET-B selectively colocalized with NF-200, indicating its presence in horizontal cells. Under basal conditions, Phospho-SAPK/JNK was detected in ganglion axons, Inner plexiform layer and in horizontal-like-structure of the OPL. After 1 day of continuous illumination, the same immunoreactivity was observed, although new immunoreactivity appeared in cell bodies of the Inner nuclear layer (INL). Western blot showed an increase of Phospho-SAPK/JNK expression after 1 day of illumination respect to the basal conditions. In conclusion, ET-A receptor could be located on bipolar processes of cone pathway and ET-B in horizontal cell. Endothelinergic-signaling could occur on synaptic triad affecting neuronal functions. The increase of Phospho-SAPK/JNK after 1 day of continuous illumination could imply stressing signaling triggered by dyeing photoreceptors affecting INL cells.