Light-evoked and kainic-acid-induced disc shedding by rod photoreceptors: differential sensitivity to extracellular calcium. J Comp Neurol 1986 Sep 08;251(2):185-97
Date
09/08/1986Pubmed ID
3491094DOI
10.1002/cne.902510205Scopus ID
2-s2.0-0022549366 (requires institutional sign-in at Scopus site) 16 CitationsAbstract
In order to study the light and Ca2+ dependence of disc shedding by rod photoreceptors, we have used eyecups prepared from adult Rana pipiens frogs that had been kept in constant light for 4 days. Disc shedding was initiated by a treatment involving 1 hour of darkness followed by exposure to light or by treatment with kainic acid. Maximal L-evoked disc shedding occurred quickly (within 30-60 minutes) after light onset and could be triggered by brief (15 minutes) exposure to light. L-evoked disc shedding was completely blocked by omission of Ca2+ from culture medium or by treatment with 3mM Co2+ or 12 mM Mg2+ in the presence of Ca2+ (2 mM). The response was also blocked by the organic Ca2+ antagonist nifedipine. Experiments designed to distinguish between Ca2+ dependence of the dark- or light-dependent processes necessary for shedding suggest that voltage-sensitive channels mediate a Ca2+-dependent process involved in light-triggering. Kainic acid caused a dose-dependent stimulation of disc shedding under lighting conditions (continuous culture in light or darkness) that did not normally result in a significant response in the absence of the drug. Disc shedding induced by kainic acid was similar in time course and magnitude to that induced by light. However, kainic-acid-induced disc shedding was not inhibited by medium Ca2+ reduction or by the presence of Co2+. The latter observation suggests that kainic acid activates disc shedding directly, by-passing the Ca2+-dependent process involved in the L-evoked response. The Ca2+-dependent process may involve release of an effector of disc shedding that is mimicked by kainic acid.
Author List
Besharse JC, Spratt G, Forestner DMMESH terms used to index this publication - Major topics in bold
AnimalsCalcium
Circadian Rhythm
Intracellular Membranes
Kainic Acid
Light
Nifedipine
Phagosomes
Photic Stimulation
Photoreceptor Cells
Rana pipiens
