Changements de la concentration du K⁺induits par un flash dans le vitré prérétinien du porc miniature anesthésié

Abstract

When measured with double-barreled ion-selected microelectrodes, delta K+0 is found to be heterogeneously distributed over the retinal surface. A transient fall (less than or equal to 200 microM) in delta K+0 near an arteriole wall and a transient increase (less than or equal to 500 microM) in zones free of arterioles were observed during light stimulation. In view of these findings the authors assume that the former is due to K+ uptake and transport by perivascular astrocytes, and that the latter is due to K+ siphoning by Müller cells.

Retinal vessel reaction in response to chromatic flickering light

“…Several approaches have been tried to investigate blood flow change in the retina during neuronal stimulation in humans [10,8,12,13,14,17,25,26,27,28,30,31,32,33,39,40,42,37,44,45,52]. In one study the blue-field entoptic technique was used and an increase in retinal white blood cell flux in response to flicker stimulation was reported in healthy volunteers [44].…”

“…Recent investigations with techniques assessing ocular blood flow have shown that such a mechanism operates at the optic nerve head and retina in cats [5,18,38,36,47,51], rabbits [50], mini-pigs [31], primates [2,3,15] and humans [8,9,10,11,12,13,14,17,25,26,27,28,30,32,31,33,39,40,41,42,44,45,52].…”

“…Methods used to assess ocular blood flow parameters in these studies include the labeled deoxyglucose method by Sokoloff [3], the labeled microspheres method [18,51], indirect measurements of neuronal activity from changes in [K+] in the vitreous humor with ion sensitive electrodes [31], measurements with double-tube oxygen electrodes [24], the entoptic blue field technique [44], pulsatile Doppler sonography [30], laser Doppler velocimetry [11,35], laser Doppler flowmetry by Riva [5,10,8,26,40,41], scanning laser Doppler flowmetry (HRF) [30], laser-targeted angiography [49], assessment of retinal vessel diameter off-line from fundus photographs [12,13] and on-line assessment of retinal vessel diameter with the Retinal Vessel Analyzer [20,21,22,32,33,45,52]. It is important to note that all the above mentioned methods are based on different principles assessing only parts of the complex nature of blood flow in the ocular region.…”

Confocal Microscopy and Computer‐assisted Image Reconstruction of Astrocytes in the Mammalian Retina

“…In cat and rat, individual astrocytes can be simultaneously engaged in contacts with both vessels and axonal bundles. In the rat retina, this feature is not readily visible by conventional fluorescence microscopy and the usefulness of confocal microscopy appears evident, since optic nerve humour and the vasculature provided by intercalating astrocytes would accommodate a recent electrophysiological observation in the miniature pig, where, after a light flash, the amplitude of change in extracellular potassium concentration in the preretinal vitreous was found to depend on the distance between the site of measurement and the neighbouring vessel (Poitry-Yamate et al, 1990). This observation has been tentatively explained by an uptake of potassium from the vitreous body by perivascular astrocytes and its release into the vessel.…”