title: Electron probe microanalysis of calcium release and magnesium uptake by endoplasmic reticulum in bee photoreceptors.
abstract: Honey bee photoreceptors contain large sacs of endoplasmic reticulum (ER) that can be located unequivocally in freeze-dried cryosections. The elemental composition of the ER was determined by electron probe x-ray microanalysis and was visualized in high-resolution x-ray maps. In the ER of dark-adapted photoreceptors, the Ca concentration was 47.5 +/- 1.1 mmol/kg (dry weight) (mean +/- SEM). During a 3-sec nonsaturating light stimulus, approximately 50% of the Ca content was released from the ER. Light stimulation also caused a highly significant increase in the Mg content of the ER; the ratio of Mg uptake to Ca released was approximately 0.7. Our results show unambiguously that the ER is the source of Ca2+ release during cell stimulation and suggest that Mg2+ can nearly balance the charge movement of Ca2+.
authors.affiliation: Institut für Zoologie, Universität Regensburg, Federal Republic of Germany.
authors.forename: O
authors.initials: O
authors.lastname: Baumann
authors.forename: B
authors.initials: B
authors.lastname: Walz
authors.forename: A V
authors.initials: AV
authors.lastname: Somlyo
authors.forename: A P
authors.initials: AP
authors.lastname: Somlyo
mesh_terms: D000818:Animals; D001516:Bees; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D004577:Electron Probe Microanalysis / Q000379:methods; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000528:radiation effects / Q000648:ultrastructure; D008027:Light; D008274:Magnesium / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D015398:Signal Transduction
chemical_list: D008274:Magnesium; D002118:Calcium