title: Rapid coupling of calcium release to depolarization in Limulus polyphemus ventral photoreceptors as revealed by microphotolysis and confocal microscopy.
abstract: Microphotolysis and confocal microscopy were used to investigate the timing of calcium release and of the electrical response in Limulus polyphemus ventral photoreceptors. The fluorescent dyes Fluo-3 and Calcium Green-5N were used to monitor local Ca2+ elevations. Photolysis of caged inositol trisphosphate (InsP3) close to the plasma membrane of the light-sensitive rhabdomeral (R-) lobe resulted in Ca2+ elevation within 10-20 msec, 20-45 msec before the physiological response to light normally would be detected. Inward ionic current flow and depolarization followed InsP3-induced calcium release within 2.5 +/- 3.3 msec. Voltage-clamping the cells and removal of extracellular Ca2+ did not affect the timing of the Ca2+ elevation that followed the photolysis of caged InsP3 or its relationship to the electrical response. In contrast to the physiological response to light, which only released calcium within the R-lobe, photolysis of InsP3 elevated Cai in both lobes, although with much greater effect in the R-lobe, as compared with the bulk of the A-lobe, suggesting the presence of InsP3-sensitive calcium stores in both lobes. Photolysis of caged calcium [o-nitrophenyl EGTA (NPE)] at the edge of the R-lobe activated an inward ionic current within 1.8 +/- 0.7 msec. This NPE-induced current reversed at a membrane potential of 10 +/- 6 mV in the range typical of that of the light-activated current under physiological conditions. Calcium release, therefore, activates an inward current rapidly enough to contribute to the electrical response to light.
authors.affiliation: Department of Zoology, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: K
authors.initials: K
authors.lastname: Ukhanov
authors.forename: R
authors.initials: R
authors.lastname: Payne
mesh_terms: D000200:Action Potentials; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000528:radiation effects; D000814:Aniline Compounds / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004331:Drosophila melanogaster / Q000502:physiology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000528:radiation effects; D005456:Fluorescent Dyes / Q000032:analysis; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006737:Horseshoe Crabs / Q000502:physiology; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000528:radiation effects; D008832:Microchemistry; D018613:Microscopy, Confocal; D009900:Optic Nerve / Q000502:physiology*; D009930:Organic Chemicals; D018408:Patch-Clamp Techniques; D010782:Photolysis; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology* / Q000648:ultrastructure; D015290:Second Messenger Systems / Q000502:physiology* / Q000528:radiation effects; D013045:Species Specificity; D013873:Thionucleotides / Q000494:pharmacology; D014966:Xanthenes / Q000032:analysis
chemical_list: D000814:Aniline Compounds; D005456:Fluorescent Dyes; D009930:Organic Chemicals; D013873:Thionucleotides; D014966:Xanthenes; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; C071336:calcium green; D006153:Guanosine Diphosphate; C085112:2-nitrophenyl-EGTA; C059715:Fluo-3; D004533:Egtazic Acid; C029273:P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate; C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002118:Calcium