Light-induced changes in extracellular calcium concentration in the compound eye of Calliphora, Locusta and Apis.

Ion-selective microelectrodes inserted into the compound eyes of Calliphora, Locusta and Apis were used to monitor the changes in extracellular concentration of Ca (Ca) brought about by a 1-min exposure to white light (maximal luminous intensity ca. 10 cd/m). In the blowfly retina such stimulation causes a decrease in Ca. At high light intensities the Ca signal is phasic, falling over about 6 s to a transient light-induced minimum (ΔCa= -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 ΔCa of -13.8% ± 1.6% ( n = 10), and at the plateau the Ca decrease is-13.2% ± 1.5%. In honey-bees Ca 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 Ca. Therefore the species differences might be interpreted as a consequence of differences in the intracellular dark concentration of Ca. [ABSTRACT FROM AUTHOR]