Light-induced extracellular changes of calcium and sodium concentrations in the Planarian ocellus.
Ion-selective double-barreled microelectrodes inserted into a planarian ocellus were used to monitor the ocellus potential and the changes in extracellular concentrations of Ca2+ (Ca(o)) and Na+ (Na(o)) caused by a 0.5-sec light flash or sustained (120s) illumination. Ca(o) and Na(o) were slightly decreased following a flash. Sustained illumination caused a biphasic change in Ca(o) (a rapid decrease followed by a slow increase) and a tonic decrease in Na(o). When Na+ in the planarian saline was replaced by Li+ or choline+, the increase in Ca(o) was prevented: sustained illumination induced only a decrease in Ca(o). These results suggest that illumination induces influxes of both Ca+ and Na+ into planarian photoreceptors, and that the Ca2+ influx is rapidly followed by a Na-dependent Ca2+ efflux due to Na-Ca exchange.
Department of Biology, Osaka Medical College, Takatsuki, Osaka, Japan. bio002@art.osaka-med.ac.jp
K
K
Azuma
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004563:Electrochemistry; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism*; D008027:Light; D009994:Osmolar Concentration; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology / Q000528:radiation effects; D010932:Planarians / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D002118:Calcium