The Effect of Hyperosmotic Stress and Protein Kinase A Manipulation on Ciliary Beat Frequency at 20oC

Abstract

Mannitol is sometimes administered as an aerosol to increase mucociliary clearance. The aim of the study was to investigate the role of mannitol on regulation of ciliary beat frequency, a component of mucociliary clearance; and to investigate the interplay between mannitol induced hyperosmotic stress and protein kinase A. Ciliated nasal epithelial cells were collected from ten healthy volunteers undergoing surgery. Using video microscopy, ciliary beat frequency was measured at 20^oC in the presence of protein kinase A modulators with or without 400mM mannitol in medium 199. Protein kinase A activation with db-cAMP (1mM) in isosmotic medium significantly increased ciliary beat frequency (p<0.05) but kinase inhibition was without effect and similar to control. A reversible 75% reduction in ciliary beat frequency occurred when cells were exposed to a hyperosmotic solution of 400mM mannitol in normal culture medium. The ciliary beat frequency under hyperosmotic conditions was slightly lowered further when PKA was activated whereas PKA inhibition had a slight stabilizing effect; almost the opposite of what was observed under isosmotic conditions. In conclusion protein kinase activation in isosmotic medium increases ciliary beat frequency at 20^oC and its inhibition has no effect. Mannitol induced hyperosmotic stress reduces ciliary beat frequency and this reduction is affected by PKA manipulation in a complex manner.