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Barium reverses the transretinal potassium gradient of the amphibian retina
P A Coleman1, P L Carras, R F Miller
1Ophthalmology Department, Washington University, School of Medicine, St. Louis, MO 63110.
Abstract:
Barium chloride (Ba2+) was added to the bathing medium of the perfused retina-eyecup preparation of the tiger salamander. The electroretinogram (ERG) and intraretinal extracellular potassium activity ([K+]o) were analyzed using a double-barrel electrode, one of which was ion-selective for K+. The action of Ba2+ on the ERG was to attenuate the c-wave/slow PIII complex. In addition, Ba2+ dramatically decreased the [K+]o in the outer retina, enough to reverse the transretinal potassium gradient. These findings, together with the known properties of Müller cell K+ channels, form the basis of an explanation of why Ba2+ blocks slow PIII and not the b-wave of the ERG.