The mechanism mediating regenerative intercellular Ca2+ waves in the blowfly salivary gland.
Intercellular Ca2+ signaling in intact salivary glands of the blowfly Calliphora erythrocephala was studied by fluorimetric digital imaging combined with microinjection of putative messenger molecules. Iontophoretic injection of D-myo-inositol 1,4, 5-trisphosphate (InsP3) into salivary gland cells evoked regenerative intercellular Ca2+ waves that spread through the impaled cell and several rows of surrounding cells. Ca2+ increases induced by microinjection of Ca2+ ions were confined to the injected cells and their nearest neighbors. Depletion of intracellular Ca2+ stores by thapsigargin pre-treatment did not alter the time course of the Ca2+ increase caused by Ca2+ injection. However, activation of Ca2+ release became clearly evident when Ca2+ was injected in the presence of serotonin (5-HT). Under these conditions, injection of Ca2+ triggered intercellular Ca2+ waves that consecutively passed through >10 cells. The phospholipase C inhibitor U73122 blocked 5-HT-induced Ca2+ increases but did not affect InsP3-dependent Ca2+ spiking and intercellular Ca2+ wave propagation. The results demonstrate that propagation of agonist-evoked Ca2+ waves in the blowfly salivary gland requires supra-basal [InsP3] but does not depend on feedback activation of phospholipase C. We conclude that the intra- and intercellular transmission of these Ca2+ waves is mediated by diffusion of Ca2+ and Ca2+-induced Ca2+ release via the InsP3 receptor channel.
Zimmermann
B
B
Institut für Zoophysiologie und Zellbiologie, Universität Potsdam, D-14471 Potsdam, Germany. zimmerm@rz.uni-potsdam.de
Walz
B
B
D000818:Animals; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D004058:Diffusion; D004175:Diptera / Q000378:metabolism*; D004789:Enzyme Activation; D004963:Estrenes / Q000494:pharmacology; D005246:Feedback; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000008:administration & dosage / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008845:Microinjections; D011760:Pyrrolidinones / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D012469:Salivary Glands / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D015220:Calcium Channels; D004963:Estrenes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011760:Pyrrolidinones; D018160:Receptors, Cytoplasmic and Nuclear; D012702:Serotonin Antagonists; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D012701:Serotonin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D002118:Calcium