Effects of albuterol enantiomers on ciliary beat frequency in ovine tracheal epithelial cells

Abstract

Frohock, Jeffrey I., Corrine Wijkstrom-Frei, and Matthias Salathe. Effects of albuterol enantiomers on ciliary beat frequency in ovine tracheal epithelial cells. J Appl Physiol 92: 2396-2402, 2002. First published February 8, 2002 10.1152/japplphysiol.00755.2001.-␤ 2-Adrenergic agonists stimulate ciliary beat frequency (CBF), an integral part of mucociliary clearance. To evaluate the differential effects of albuterol enantiomers and their racemic mixture on ciliary function, CBF and intracellular calcium were measured at room temperature from single ovine airway epithelial cells with use of digital videomicroscopy. Baseline CBF was 7.2 Ϯ 0.2 (SE) Hz (n ϭ 80 measurements). R-albuterol (10 M to 1 mM) stimulated CBF in a dose-dependent manner to maximally 24.4 Ϯ 5.4% above baseline. Racemic albuterol stimulated CBF to maximally 12.8 Ϯ 3.6% above baseline, a significantly lower increase compared with R-albuterol alone, despite identical R-enantiomer amounts in both groups. Simultaneous recordings of intracellular calcium concentration and CBF from single cells indicated that the CBF increase in response to R-albuterol was mediated through ␤-receptors and stimulation of protein kinase A, in a calcium-dependent and -independent fashion. S-albuterol had a negligible effect on CBF and did not change intracellular calcium. Together, these results suggest that R-albuterol is more efficacious than racemic albuterol in stimulating CBF. Thus S-albuterol may interfere with the ability of R-albuterol to increase CBF. airway; calcium; beta-agonists; signaling ␤-AGONISTS HAVE BEEN SHOWN to stimulate the mucociliary transport rate (4, 5, 22), and thus they are used clinically to improve mucociliary clearance (10, 14, 15, 18), a major airway host defense mechanism. Ciliary beating is an integral part of the mucociliary transport apparatus, and it has been well established that ␤ 2 -adrenergic agonists stimulate ciliary beat frequency (CBF) in a variety of airway epithelial cells (11,27,33,34). Therefore, the increase in CBF is believed to be the main contributor to higher mucociliary transport rates seen after ␤ 2 -agonist administration. Albuterol, the most commonly used ␤ 2 -agonist in a clinical setting, possesses two stereoisomers due to an asymmetric carbon adjacent to the aromatic ring. The R-enantiomer binds to the ␤ 2 -adrenoceptor, leading to cAMP production, whereas the S-enantiomer has an over 100-fold lower affinity to the receptor. In addition, some recent data indicate that the S-enantiomer may have properties not usually associated with ␤ 2 -agonists, such as smooth muscle contraction through intracellular calcium concentration ([Ca 2ϩ ] i ) elevation (13) and other side effects (for review, see Ref. 8). Usually, racemic albuterol mixtures are used in a clinical setting. These mixtures bring with them the potential for divergent responses of different cellular functions for each of the enantiomers. We therefore conducted a study to compare the effects of the two enantiomers as well as the racemic mixture of albut...

<i>In Vitro</i> Evaluation of the Ciliary Beat Frequency of the Rat Nasal Epithelium Using a High-Speed Digital Imaging System

“…Stimulation of cAMP-dependent PKA seems to play an important role as the next step in the β-AR signaling pathway to stimulate CBF. Many β-adrenergic agonists such as isoproterenol, [24][25][26][27] SBM, 22,28) TBl, 11,13) fenoterol, 29) and salmeterol 30,31) have been used in previous studies, but SBM and TBL were used in the present study to confirm the validity of our in vitro evaluation system. It has been reported that R-SBM and racemic SBM increased CBF by 24 and 13%, respectively, in a dose-dependent manner (10 µm to 1 mm).…”

“…20) Many investigators have extensively studied the regulation of CBF using ciliated epithelial cells and have clarified that β-adrenergic agonists stimulate the CBF of ciliated epithelial cells. 21) β-Adrenergic agonists have been shown to have various effects on epithelial cells, such as the stimulation of CBF 21,22) and chloride secretion toward the airway lumen, 23) which could contribute to the enhanced mucociliary function by β-adrenergic agonists. It has been reported that β-AR activation in ciliated cells increased CBF through the fol- lowing two mechanisms: a calcium-coupled mechanism and calcium-independent mechanism.…”

(R)-Albuterol Elicits Antiinflammatory Effects in Human Airway Epithelial Cells via iNOS

“…After expansion, passage-2 NHBE cells were seeded on plastic 6-or 12-well culture plates at a density of 1.0 ϫ 10 4 cells/cm 2 . Medium (modified bronchial epithelial cell basal medium) was changed every other day until cultures were 80-90% confluent, at which time the cells were incubated in medium, from which bovine pituitary extract and human recombinant epidermal growth factor were removed for 24 h to force cells into a quiescent, nonproliferative state.…”

Real-time analysis of cAMP-mediated regulation of ciliary motility in single primary human airway epithelial cells

“…Agonists of G␣ s -coupled receptors and forskolin that increase intracellular cAMP through stimulation of transmembrane adenylyl cyclases (tmACs) all stimulate CBF, and these effects can be blocked with inhibitors of cAMP-dependent protein kinase A (PKA) (Di Benedetto et al, 1991;Frohock et al, 2002;Lansley et al, 1992;Sanderson and Dirksen, 1989;Tamaoki et al, 1989b;Verdugo et al, 1980;Wyatt et al, 1998;Yang et al, 1996). In analogy to the situation in Paramecium (Hamasaki et al, 1991;Hamasaki et al, 1989), cAMP possibly regulates CBF by activating PKA localized to the axoneme by its A kinase anchoring protein (Kultgen et al, 2002).…”