Cytosolic calcium transients: spatial localization and role in Drosophila photoreceptor cell function.
Drosophila phototransduction is a phosphoinositide-mediated and Ca(2+)-regulated signaling cascade ideal for the dissection of feedback regulatory mechanisms. To study the roles of intracellular Ca2+ ([Ca2+]i) in this process, we developed novel techniques for the measurement of [Ca2+]i in intact photoreceptors. We genetically engineered flies that express a UV-specific rhodopsin in place of the normal rhodopsin, so that long wavelength light can be used to image [Ca2+]i changes while minimally exciting the photoreceptor cells. We show that activation with UV generates [Ca2+]i increases that are spatially localized to the rhabdomeres and that are entirely dependent on the influx of extracellular Ca2+. Application of intracellular Ca2+ chelators of varying affinities demonstrates that the Ca2+ influx initially generates a large-amplitude transient that is crucial for negative regulation. Internal Ca2+ stores were revealed by discharging them with thapsigargin. But, in contrast to proposals that IP3-sensitive stores mediate phototransduction, thapsigargin does not mimic or acutely interfere with photoexcitation. Finally, we identify a photoreceptor-specific PKC as essential for normal kinetics of [Ca2+]i recovery.
Ranganathan
R
R
Department of Biology, University of California at San Diego, La Jolla 92093-0649.
Bacskai
B J
BJ
Tsien
R Y
RY
Zuker
C S
CS
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics / Q000378:metabolism*; D004553:Electric Conductivity; D005110:Extracellular Space / Q000378:metabolism; D005818:Genetic Engineering; D007700:Kinetics; D018613:Microscopy, Confocal; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure; D011493:Protein Kinase C / Q000378:metabolism; D012243:Rhodopsin / Q000235:genetics / Q000528:radiation effects; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014466:Ultraviolet Rays
D013729:Terpenes; D019284:Thapsigargin; D012243:Rhodopsin; D011493:Protein Kinase C; D002118:Calcium