Effect of cAMP on ciliary function in rabbit tracheal epithelial cells

Abstract

To study the effect of adenosine 3',5'-cyclic monophosphate (cAMP) on respiratory ciliary activity, we measured ciliary beat frequency (CBF) of rabbit tracheal epithelium by a photoelectric method in response to cAMP analogues and agents that can increase endogenous cAMP production. Addition of 8-bromo-cAMP dose dependently enhanced CBF, with the maximal increase and the concentration necessary to produce a half-maximal response (KD) being 31.0 +/- 3.4% (SE) (P less than 0.001) and 3.2 +/- 1.5 x 10(-7) M, respectively. Other structurally dissimilar cAMP analogues dibutyryl cAMP and chlorophenylthio-cAMP likewise caused increases in CBF. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and the adenylate cyclase stimulator forskolin also augmented CBF in a dose-dependent fashion and were accompanied by the increases in intracellular concentrations of cAMP. Ciliary discoordination was not observed in any of the experiments. These results suggest that cAMP may accelerate mucociliary clearance through the activation of ciliary motility and that intracellular cAMP levels appear to be an important determinant for the lung mucociliary transport functions.

Interplay between the NO pathway and elevated [Ca2+]i enhances ciliary activity in rabbit trachea

“…The discrepancy between our findings and those of Kobayashi et al may be due to the relatively high concentration of TPA used by the latter. Direct activation of PKA by dB-cAMP induced a relatively small enhancement of CBF (•20%), in agreement with previously reported results (Tamaoki et al 1989). A similar response was obtained after the addition of forskolin (FmaxÏFo = 1·3).…”

“…Similarly, dB-cAMP enhanced CBF by 20% and did not influence [Ca¥]é (n = 6 coverslips from 5 rabbits). These results confirm previous findings that direct activation of PKA by dB-cAMP in mammalian ciliary cells produces a small (•20-30%) enhancement in CBF (Tamaoki et al 1989). However, inhibiting PKA failed to attenuate the biphasic rise of [Ca¥]é or CBF enhancement induced by extracellular ATP (n = 3 coverslips from 2 rabbits; data not shown).…”

“…However, when [Ca¥]é was directly elevated by exposing an ¬_NAME-treated cell to ionomycin (1 ìÒ), CBF increased 2_fold, mimicking the effects of ionomycin on untreated cells (cf. rows 1 and 5 in Table 1 Adenylyl cyclase andÏor protein kinase A are not involved in ciliary activation by ATP It has been reported that several isoenzymes of adenylyl cyclase (AC) can be directly activated by Ca¥ (Antoni, 1997), thereby stimulating production of cAMP, a wellknown activator of CBF (Bonini et al 1988;Tamaoki et al 1989). In order to determine whether extracellular ATP enhanced CBF through a cAMP-dependent pathway, three experimental approaches were used: in the first, the cells were exposed to forskolin (25 ìÒ), a direct activator of AC; in the second, the cells were exposed to dibutyryl-cAMP (dB_cAMP, 100-400 ìÒ); and in the third approach, the cells were pre-treated with Rp-cAMPS (100 ìÒ), a potent PKA inhibitor (Ki = 11 ìÒ), and the effects of ATP were determined.…”

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

“…al., 2002; Morse et al, 2001;Smith et al, 1996;Tamaoki et al, 1989b;Wyatt et al, 2005;Wyatt et al, 1998). Adrenergic drugs, known to increase CBF (Sanderson and Dirksen, 1989;Wyatt et al, 1998;Yang et al, 1996), also increase intracellular cAMP levels.…”

“…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).…”