The interaction between the neuroretina and the retinal pigment epithelium : an electrophysiological study of the effects of possible messenger substances and their analogues
Sammanfattning: The retinal pigment epithelium (RPE) is of great importance in photoreceptor homeostasis. The photoreceptors are highly specialized cells which cannot survive without the RPE. It has been postulated that messenger substances are involved in the interaction between the RPE and the inner retina. In the present study, the effects on the light induced electrical responses of the eye of some possible messenger substances and their analogues were investigated. The a-, b- and c-waves of the corneal electroretinogram (ERG) and the standing potential of the eye (SP) were investigated dming simultaneous perfusion of the vitreous cavity of albino rabbit eyes with test substances alternating with a control solution. The contralateral eye of each rabbit was used as a control. To further analyze the effect on the ERG c-wave, a new in vivo method was applied. A microelectrode is advanced through the retina into the subretinal space, enabling recording of the transepithelial potential (TEP) and the slow Pili dming simultaneous perfusion of the vitreous cavity. Phenylephrine, an a.1-adrenergic receptor agonist, in a low concentration increased the c-wave and the SP, whereas clonidine, an o:.z-adrenergic receptor agonist, had similar effects on the c-wave but at higher concentration. The b-wave was also slightly elevated but there was no significant effect on the a-wave. Phenylephrine increased the TEP, while the slow Pili was reduced. These results seem to indicate that a-adrenergicreceptors are present on the apical membrane of the RPE. The effect on the b-wave and the slow Pili suggests a-adrenergic effects also on the inner retina. The stable cyclic AMP analogue, Sp-cAMPS, increased the c-wave amplitude and the SP level There was also an effect on the b-wave, but the a-wave was not affected. Both the TEP and the slow Pili were elevated. The results showed that Sp-cAMPS influences the electrophysiological properties of both the RPE and the inner retina. PhXA41, a PGF2a analogue, which is a new intraocular pressure reducing agent, did not affect the ERG and the SP at low doses. At higher doses, PhXA41 and PGF,. increased the c-wave amplitude and the SP level, while there was no effect on the a- and b-waves. The c-wave elevation was due to a reduction in slow Pili, while the TEP was not affected, indicating that receptor binding sites for PGF2• are present on the Muller cell membrane. Serotonin was shown to affect the c-wave of the ERG and the SP. The c-wave amplitude elevation was caused by an elevation of the TEP while the slow Pili was unaffected. The effects of different serotonin agonists and antagonists were also studied. The results indicate the presence of 5-HTz receptors on the RPE. There is a possibility, however, of other types of serotonin receptors being present on the RPE as well.
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