The contributions of voltage- and time-dependent potassium conductances to the electroretinogram in rabbits
The electroretinogram (ERG) is generated by light-induced electrical activity in retinal cells. Since potassium ions and potassium conductances play a major role in determining the membrane potential of cells, changes in these are expected to affect the amplitude and pattern of the ERG. We recorded the ERG responses and the isolated P-III waves of rabbits after intraocular injections of specific blockers for potassium channels. 4-aminopyridine (4-AP) did not cause any noticeable changes in the ERG while tetraethylammonium chloride (TEA) induced time-dependent effects. Short-term (1–2 h) effects were expressed as significant augmentation of the b-wave with little change in the a-wave. At longer periods of follow-up, the a-wave increased in amplitude while the b-wave decreased. TEA augmented the amplitude of the isolated P-III wave. These effects of TEA can be explained by TEA-induced depolarization of the photoreceptors. Cesium ions and barium ions induced substantial augmentation of the b-wave. Barium but not cesium ions reduced the isolated P-III component of the ERG probably by blocking the potassium channels in the Müller cells. The augmentation of the b-wave by both barium or cesium ions is inconsistent with the Müller cells hypothesis for the ERG b-wave.(Received July 17 1998)
(Accepted February 7 1999)
Key Words: Retina; Electroretinogram; Delayed rectifier; Inward rectifier; Rabbit.
c1 Correspondence and reprint requests to: Ido Perlman, Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, P.O. Box 9649, Haifa 31096, Israel. E-mail: email@example.com
p1 Present address: W.K. Kellogg Eye Center, University of Michigan, Ann Arbor, Michigan, U.S.A.