Subcellular organization of agonist-evoked Ca(2+) waves in the blowfly salivary gland.
We have studied the subcellular organization of intra- and intercellular Ca(2+)waves elicited by the neurohormone 5-hydroxytryptamine (5-HT) in intact blowfly salivary glands by using Ca(2+)-sensitive fluorescent probes and confocal microscopy. 5-HT (3 nM) elicited repetitive Ca(2+)waves (1) that were initiated at Ca(2+)-release sites close to the basal plasma membrane, (2) that sequentially spread to the cell apex and (3) that, after a delay of 0.7 +/- 0.20 s at the cell boundaries, spread into adjacent cells. [Ca(2+)](i)increases in the adjacent cells were first detectable at those portions of the lateral plasma membrane that faced a previously activated cell. Electron microscopy revealed that the sites of Ca(2+)wave transmission between the cells are correlated with the distribution of gap junctions that cluster in the basal cell portions. The ensuing intracellular Ca(2+)wave propagated at constant velocity (27 +/- 7.3 microm/s) in the lateral cell plane. Moreover, a basally to apically propagating wavefront was detectable at the cell membrane that bordered on the neighbor that provided the excitatory signal, whereas [Ca(2+)](i)increased simultaneously both apically and basally at the opposite lateral cell border. Overall, the subcellular patterns of Ca(2+)wave propagation differed from the patterns observed in mammalian secretory epithelial cells. The findings impose some constraints on the functional significance of intra- and intercellular Ca(2+)waves and potential mechanisms underlying 5-HT-evoked fluid secretion.
Zimmermann
B
B
Institut für Zoophysiologie und Zellbiologie, Universität Potsdam, D-14471 Potsdam, Germany.zimmerm@rz.uni-potsdam.de
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004175:Diptera; D016166:Free Radical Scavengers / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D012469:Salivary Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology
D016166:Free Radical Scavengers; D012701:Serotonin; D002118:Calcium