The effect of K(+)-conductance-blocking substances on the occurrence of retinal spreading depression.
Retinal spreading depression (SD) has been thought to be generated by an abnormal increase in [K+]o in the inner plexiform layer. When a retina isolated from bullfrog was immersed in a medium conditioned for SD (low Cl- Ringer's solution), spontaneous SDs periodically occurred at a fixed interval in the dark. The effect of K(+)-conductance blocking substances (Ba2+, Cs+, TEA and 4-AP) on the occurrence of SD was studied using the concomitant changes in the field potential (spreading depression potential; SDP) as an index. These substances increased the frequency of occurrence and decreased the amplitude of the potential. According to the Müller cell theory of SDP, an increase in [K+]o depolarizes the Müller cells and the resulting extracellular current generates the potential change. Since the small amplitude of the SDP reflects the decreased K+ current, it may be said that the K(+)-buffering capacity of the Müller cells was partially reduced by the substances and that the frequency of the SD occurrence consequently increased in order to clear accumulating [K+]o from neurons with the decreased buffering capacity. The present results lend a good support to the current Müller cell theory for the occurrence of SDP.
Zoological Institute, Faculty of Science, Hiroshima University, Japan.
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Fujimoto
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Yanase
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D003864:Depression, Chemical; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects; D011892:Rana catesbeiana; D012160:Retina / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002586:Cesium; D001464:Barium; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium