Mechanical stimulation initiates intercellular Ca2+ signaling in intact tracheal epithelium maintained under normal gravity and simulated microgravity.
We investigated mechanically induced cell-to-cell Ca2+ signaling in a preparation of rabbit tracheal epithelium close to its in vivo condition. We used confocal microscopy to analyze changes in intracellular free calcium concentration ([Ca2+]i) in intact ciliated tracheal mucosal explants loaded with the Ca2+-indicator dye, fluo-3. When a single cell in the epithelium was transiently stimulated with a microprobe, [Ca2+]i increased in the stimulated cell and then increased in surrounding cells. In the absence of extracellular Ca2+, the [Ca2+]i increases had a smaller amplitude and spread to fewer cells. Treatment of the cells with thapsigargin, in the presence of extracellular Ca2+, more markedly reduced the spread of elevated [Ca2+]i. These results suggest that the propagated [Ca2+]i increases are due to mobilization of Ca2+ from intracellular stores and, possibly, the influx of extracellular Ca2+. The mechanically stimulated [Ca2+]i increases were accompanied by propagated increases in ciliary beat frequency. Since microgravity has been shown to alter signal transduction, we investigated whether simulated microgravity affects the mechanically stimulated cell-to-cell Ca2+ signaling observed in tracheal epithelium. Tissues were maintained for 3-8 d in a rotating wall vessel which simulates microgravity conditions. Cells maintained in simulated microgravity exhibited mechanically induced [Ca2+]i increases not significantly different in magnitude, in speed of propagation, or in the number of cells involved, from tissue maintained at unit gravity. Our results suggest that intercellular Ca2+ signaling coordinates cellular activity, including ciliary beating, within the tracheal epithelium in vivo and that this function is not compromised in microgravity.
Felix
J A
JA
Department of Neurobiology, School of Medicine, University of Calfornia, Los Angeles, Los Angeles, California, USA.
Chaban
V V
VV
Woodruff
M L
ML
Dirksen
E R
ER
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002478:Cells, Cultured; D003627:Data Interpretation, Statistical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D005110:Extracellular Space / Q000378:metabolism; D006112:Gravitation; D007091:Image Processing, Computer-Assisted; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013314:Stress, Mechanical; D019284:Thapsigargin / Q000494:pharmacology; D014132:Trachea / Q000166:cytology; D014893:Weightlessness
D004791:Enzyme Inhibitors; D019284:Thapsigargin; D002118:Calcium