ISSN:
1432-1351
Keywords:
Fly photoreceptor
;
Light adaptation
;
Calcium
;
Sodium
;
Pigment granule
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary Ion-selective microelectrodes inserted into the compound eyes of Calliphora were used to monitor the changes in extracellular concentration of Ca2+ and Na+ (Cao, Nao) brought about by a 1-min exposure to white light (maximal luminous intensity ≈0.1 cd/cm2). Using Ringer solution as the reference (Ca2+ = 1 mM), the dark concentration of the calcium in the retina was found to be (1.4 ± 0.4) mM (n=12). Stimulation with light reduces Cao. At intensities near maximal the Cao signal is phasic, reaching a transient minimum about 6 s after light onset $$(\Delta {\text{Ca}}_{\text{o}} {\text{ = }} - 6.28\% \pm 1.6\% ,{\text{ }}n = 20)$$ and then rising to a nearly stable plateau below the dark level (-3.3% ± 2.6%). Cao signals measured in the white-eyed mutant (chalky), which lacks pigment granules, are comparable to those in the wild type. Conclusions: (a) There are no extracellular Ca2+ binding sites that regulate light adaptation, such as were postulated by Hochstrate and Hamdorf (1985). (b) Ca2+ influx into the photoreceptors seems to be necessary for light adaptation, (c) The pigment granules have no major function in intracellular calcium regulation. The time course of the Nao signals resembles that of the Cao signals. Because the percentage concentration change is small, light-induced extracellular Na+-depletion cannot contribute to a reduced response amplitude at light adaptation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00206994
