Mechanical stimulation initiates intercellular Ca2+ signaling in intact tracheal epithelium maintained under normal gravity and simulated microgravity |
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Authors: | JA Felix VV Chaban ML Woodruff ER Dirksen |
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Affiliation: | Department of Neurobiology, School of Medicine, University of Calfornia, Los Angeles, Los Angeles, California, USA. |
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Abstract: | 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. |
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