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Zusammenfassung:
Ion-selective microelectrodes inserted into the compound eyes of Calliphora, Locusta and Apis were used to monitor the changes in extracellular concentration of Ca2+ (Cao) brought about by a 1-min exposure to white light (maximal luminous intensity ca. 103 cd/m2).
In the blowfly retina such stimulation causes a decrease in Cao. At high light intensities the Cao signal is phasic, falling over about 6 s to a transient light-induced minimum (ΔCao= -6.2% ± 0.4%, n = 20, SE) and then rising to an approximately stable plateau (-3.3% ± 0.6%). In migratory locusts the light-induced minimum corresponds to a ΔCao of -13.8% ± 1.6% (n = 10), and at the plateau the Cao decrease is-13.2% ± 1.5%. In honey-bees Cao at first decreases only slightly, by -2.6% ± 1.0% (n = 10); by the end of the 1-min stimulus the extracellular concentration averages 33.6% ± 14.6% above the dark level.
The results suggest a relationship between the position of the characteristic curve of the photoreceptor in the dark-adapted state, the occurrence of quantum bumps, and light-induced increases or decreases in Cao. Therefore the species differences might be interpreted as a consequence of differences in the intracellular dark concentration of Ca2+.
