Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB282

Poster Communications

Participation of the purinergic receptor P2X7 in modulation of rod- and cone-mediated electroretinographic responses

P. Kupenova1, E. Popova1, L. Vitanova1

1. Physiology, Medical University-Sofia, Sofia, Bulgaria.

The purinergic receptor P2X7 (P2X7R) is widely distributed in both neurons and glial cells of the retina. Its contribution to the electroretinographic (ERG) a- and b-waves has been proved by the results of application of the relatively selective agonist BzATP. The aim of our study was to clarify the P2X7R-mediated effects of the endogenous ATP on the ERG responses. Our interest was focused mostly on the comparison of the P2X7R-mediated effects on the ON (b-wave) and OFF (d-wave) responses as well as on the rod-driven and cone-driven responses. For this purpose, we studied the effects of the selective P2X7R antagonist A438079 on the frog (Rana ridibunda) ERG responses to stimuli of long (5 s) duration allowing for separation of ON and OFF responses. White diffuse light stimuli, varying within an intensity (I) range of 11 log units, were presented in the dark or under a rod-saturating background. Pure rod-driven responses were obtained by using very dim white stimuli below the cone threshold. Dark red stimuli (> 670 nm) were applied in order to isolate pure cone-driven responses in the dark. The antagonist A438079 was applied in 200 μM concentration by perfusion of frog eyecup preparations. The eyecups were prepared after anesthetizing the frogs with 500 mg/l tricaine methanesulfonate in the bathing water, followed by decapitation and pithing (AVMA Guidelines for the Euthanasia of Animals: 2013). Standard ERG recording (0.1-1000Hz bandwidth) was made. When a single photoreceptor type was stimulated in the dark, the amplitude of both ON (b-wave) and OFF (d-wave) responses was diminished by A438079. (RM-ANOVA; p<0.01, N=14 for rod responses; p<0.01(b-wave), p<0.001(d-wave), N=7 for cone responses). The effect was maximal at the lowest I and gradually diminished with increasing I. Different result was obtained when stimuli, activating both rods and cones, were applied. In the dark, mesopic stimulation produced enhancement, rather than diminution, of the b-wave amplitude (RM-ANOVA; p<0.001, N=14). In the same I range, the effect on the d-wave did not change its sign (the d-wave amplitude was diminished). Similar result was obtained under photopic background, when low-intensity cone stimulation was presented on the background of maximal, although not dynamic, rod response. The b-wave amplitude was increased (RM-ANOVA; p<0.01, N=12), while that of the d-wave was decreased (p<0.001, N=12), although the d-wave diminution was less than that obtained in the dark (p<0.01). The effect on the a-wave was always a small diminution of its amplitude, mostly in the lower I part of the dynamic range. Our results show that the endogenous ATP, through its P2X7R, potentiates the pure rod- and pure cone-driven responses to weak light stimuli. They also demonstrate that P2X7R is involved in rod-cone signal interaction, most likely at a postreceptoral level.

Where applicable, experiments conform with Society ethical requirements