ENDOTHELIN RECEPTORS IN SYNAPSES OF THE OUTER PLEXIFORM LAYER

VANESA TORBIDONI, MARÍA IRIBARNE, MAURICIO CASTAÑEDA, ANGELA M. SUBURO

Buenos Aires, Argentina.

Congreso; XVII International Congress of Eye Research; 2006

International Society for Eye Research

We have described presence of endothelin-1 and its receptors, ET-A and ET-B, in different sites of the mouse retina, including the retinal pigment epithelium (RPE), the outer plexiform layer (OPL), astrocytes, the ganglion cell layer (GCL) and vascular endothelia. After light induced retinal degeneration, we have observed that endothelinergic structures disappear from the outer plexiform layer (OPL) but ET-1 and ET-B increase in astrocytes. Besides, increases of ET-A were observed in the outer plexiform layer of retinas treated with endotoxin. Our purpose was identified cells in OPL bearing ET receptors, possible sites of endothelinergic signaling. We also evaluated changes in ET receptors 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 200 kd neurofilament (marker for horizontals). In animals under basal illumination, ET-A immunofluorescence demonstrated a layer of regularly distributed varicosities in OPL. Photoreceptors processes labeled with SV-2 presented similar appearance. However there was not colocalization between these markers. RT-97 neither colocalized with ET-A terminals of the OPL. ET-B immunofluorescence selectively colocalized with RT-97 immunofluorescence, indicating its presence in horizontal cells. No changes could be detected in ET-A or ET-B at the OPL after exposure to 1,500 lux during 24 hours but this exposure increased ET-B immunofluorescence in Müller cells. These data suggest that ET-A receptor could be located on bipolar processes of OPL and ET-B in horizontal cells. Endothelinergic-signaling could exist in the synaptic triad affecting neuronal functions. After 1 days of continuous illumination ET-B increased in Müller probably reflecting changes of endothelin levels.