Hyaluronic Acid in Cultured Ovine Tracheal Cells and Its Effect on Ciliary Beat Frequency In Vitro

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Abstract
Hyaluronic acid (hyaluronan, or HA) is secreted by submucosal glands, but its function in airway secretions other than influencing the rheology of mucus is not fully understood. HA is known to modulate cell behavior and to enhance sperm motility. Because sperm tails and cilia have the same microtubular structure, we studied the effect of HA on ciliary beat frequency (CBF) in vitro. CBF of cultured ovine airway epithelial cells was measured continuously by digital video microscopy. After removal of endogenous HA by hyaluronidase, cells were exposed to 50 to 100 microg/mL of HA at different times in culture. No change in CBF in response to HA was seen in cells cultured less than 7 days. After 7 days, however, 6 of 10 measured cells (from three different sheep) showed a transient CBF increase from a baseline of 6.4 +/- 0.3 Hz (mean +/- SE) to 7.4 +/- 0.4 Hz or 16% above baseline (p < 0.05). At these time points (but not before), cytochemical staining was positive for endogenous HA using a biotinylated HA-binding protein. These data suggest that HA can increase CBF of tracheal epithelial cells only late in culture when HA is able to bind to an unspecified cell surface structure. Because this binding has a physiological effect, we hypothesize that it is an HA-binding receptor, that is either transiently expressed late in culture or initially destroyed by the protease treatment for cell dispersion.