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Light-induced changes of extracellular ions and volume in the isolated chick retina–pigment epithelium preparation

Published online by Cambridge University Press:  07 July 2001

A.V. DMITRIEV
Affiliation:
Departments of Physiology and Ophthalmology, University of California, San Francisco
V.I. GOVARDOVSKII
Affiliation:
Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
H.N. SCHWAHN
Affiliation:
Department of Pathophysiology of Vision and Neuroophthalmology, University Eye Hospital, Tübingen, Germany
R.H. STEINBERG
Affiliation:
Departments of Physiology and Ophthalmology, University of California, San Francisco

Abstract

To better understand the mechanisms of extracellular space volume regulation and their possible effects on retinal function, light-induced changes in the concentrations of the principal extracellular ions (Na+, K+, Ca2+, and Cl) were measured with ion-sensitive microelectrodes in the chick retina–pigment epithelium–choroid preparation. Changes of extracellular space volume were assessed by measuring the concentration of an impermeant marker, tetramethylammonium. In the inner retina, transient ON/OFF Na+ decrease was about twice as large as K+ increase, and the charge difference was compensated by a decrease in Cl concentration. The ion changes were accompanied by extracellular space-volume decreases here. In the subretinal space, [Na+]o increase was about twice as large as K+ decrease, yet [Cl]o also decreased; this was accompanied by a sustained extracellular space-volume increase. The ionic changes in the inner retina are consistent with a model of extracellular space-volume regulation which assumes that neuronal depolarization causes net uptake of NaCl, cell swelling, and extracellular space shrinkage. However, to prevent the apparent violation of electroneutrality in the subretinal space, our simple model should be expanded to include the involvement of unidentified anion(s). Substantial changes in the subretinal space volume may influence interaction between the neural retina and pigment epithelium. Among ionic changes, only the light-induced [K+]o decrease around the photoreceptors and the [Ca2+]o increase near the photoreceptor bodies and synaptic terminals are large enough (−25% and 7.5%, respectively) to be likely candidates for integrated intercellular signaling.

Type
Research Article
Copyright
1999 Cambridge University Press

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