Am. J. Respir. Cell Mol. Biol., Volume 18, Number 5, May, 1998 602-610

Mechanical Stimulation Initiates Intercellular Ca²⁺ Signaling in Intact Tracheal Epithelium Maintained under Normal Gravity and Simulated Microgravity

Jennifer A. Felix, Victor V. Chaban, Michael L. Woodruff, and Ellen R. Dirksen

Department of Neurobiology, School of Medicine, University of Calfornia, Los Angeles, Los Angeles, California

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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