WALZ, B and BAUMANN, O and ZIMMERMANN, B and CIRIACYWANTRUP, EV (1995) CAFFEINE-SENSITIVE AND RYANODINE-SENSITIVE CA2+-INDUCED CA2+ RELEASE FROM THE ENDOPLASMIC-RETICULUM IN HONEYBEE PHOTORECEPTORS. JOURNAL OF GENERAL PHYSIOLOGY, 105 (4). pp. 537-567. ISSN 0022-1295,
Full text not available from this repository.Abstract
Light stimulation of invertebrate microvillar photoreceptors causes a large rapid elevation in Ca-i, shown previously to modulate the adaptational state of the cells. Ca-i rises, at least in part, as a result of Ins(1,4,5)P-3-induced Ca2+ release from the submicrovillar endoplasmic reticulum (ER). Here, we provide evidence for Ca2+-induced Ca2+ release (CICR) in an insect photoreceptor. In situ microphotometric measurements of Ca2+ fluxes across the ER membrane in permeabilized slices of drone bee retina show that (a) caffeine induces Ca2+ release from the ER; (b) caffeine and Ins(1,4,5)P-3 open distinct Ca2+ release pathways because only caffeine-induced Ca2+ release is ryanodine sensitive and heparin insensitive, and because caffeine and Ins(1,4,5)P-3 have additive effects on the rate of Ca2+ release; (c) Ca2+ itself stimulates release of Ca2+ via a ryanodine-sensitive pathway; and (d) cADPR is ineffective in releasing Ca2+. Microfluorometric intracellular Ca2+ measurements with fluo-3 indicate that caffeine induces a persistent elevation in Ca-i. Electrophysiological recordings demonstrate that caffeine mimics all aspects of Ca2+-mediated facilitation and adaptation in drone photoreceptors. We conclude that the ER in drone photoreceptors contains, in addition to the Ins(1,4,5)P-3-sensitive release pathway, a CICR path way that meets key pharmacological criteria for a ryanodine receptor. Coexpression of both release mechanisms could be required for the production of rapid light-induced Ca2+ elevations, because Ca2+ amplifies its own release through both pathways by a positive feedback. CICR may also mediate the spatial spread of Ca2+ release from the submicrovillar ER toward more remote ER subregions, thereby activating Ca2+-sensitive cell processes that are not directly involved in phototransduction.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | LIMULUS VENTRAL PHOTORECEPTORS; CYCLIC ADP-RIBOSE; JUNCTIONAL TERMINAL CISTERNAE; INDUCED CALCIUM RELEASE; DRONE APIS-MELLIFERA; FAST SKELETAL-MUSCLE; SEA-URCHIN EGGS; INOSITOL TRISPHOSPHATE; SARCOPLASMIC-RETICULUM; INTRACELLULAR CALCIUM; |
| Depositing User: | Dr. Gernot Deinzer |
| Last Modified: | 19 Oct 2022 08:38 |
| URI: | https://pred.uni-regensburg.de/id/eprint/52668 |
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