A low [Ca2+]i-induced enhancement of cAMP-activated ciliary beating by PDE1A inhibition in mouse airway cilia

Abstract

This study demonstrated that PDE1 (phosphodiesterase 1) existing in the ciliary beat frequency (CBF)-regulating metabolon regulates CBF in procaterol-stimulated lung airway ciliary cells of mouse. Procaterol (an β-agonist) increased the ciliary bend angle (CBA) and CBF via cAMP accumulation in the ciliary cells of mice: interestingly, the time course of CBF increase was slower than that of CBA increase. However, IBMX (3-isobutyl-1-methylxanthine, an inhibitor of PDE) increased CBA and CBF in an identical time course. Lowering an intracellular Ca concentration ([Ca]) caused by switching to an EGTA-containing Ca-free solution from normal one elevated the procaterol-induced increasing rate of CBF. These observations suggest that Ca-dependent PDE1 controls cAMP-stimulated CBF increase. Either application of 8MmIBMX (8-methoxymethyl-IBMX, a selective PDE1 inhibitor), BAPTA-AM (an intracellular Ca chelator), or calmidazolium (an inhibitior of calmodulin) alone increased CBA and CBF in the lung airway ciliary cells and increased cAMP contents in the isolated lung cells, and like IBMX, each application of the compound made the time courses of CBA and CBF increase stimulated by procaterol identical. The immunoelectron microscopic examinations revealed that PDE1A exists in the space between the nine doublet tubules ring and plasma membrane in the lung airway cilium, where the outer dynein arm (a molecular motor regulating CBF) functions. In conclusion, PDE1A is a key factor slowing the time course of the procaterol-induced increase in CBF via degradation of cAMP in the CBF-regulating metabolon of the mouse lung airway cilia.

[Ca2+]i modulation of cAMP‐stimulated ciliary beat frequency via PDE1 in airway ciliary cells of mice

“…However, previous studies showed that reduction of [Ca 2+ ] i induced various CBF responses in airway ciliary cells; no change (Komatani‐Tamiya et al., ; Li et al., ), a decrease (Hayashi et al., ; Matsubara et al., ; Narumoto et al., ) or an increase (Kogiso et al., , ). The Ca 2+ and cAMP signals have been recognized independently to increase CBF in nasal ciliary cells (Smith et al., ).…”

“…Ciliary beating is of particular importance in the activation of mucociliary clearance in the airway (Afzelius, ; Salathe, ; Wanner, Salathe, & O'Riordan, ) and is regulated by Ca 2+ and cAMP (Salathe, ; Smith, Shellard, Dhillon, Winter, & Mehta, ; Wanner et al., ). The activities of ciliary beating are assessed by two parameters, ciliary bend angle (CBA) and ciliary beat frequency (CBF), in airway ciliary cells (Ikeuchi et al., , ; Kogiso et al., ; Komatani‐Tamiya et al., ). Increases in CBA and CBF have been shown to enhance ciliary transport in experimental conditions (Komatani‐Tamiya et al., ).…”

“…This indicates that the CBF‐regulating pathway is distinct from the CBA‐regulating one in airway ciliary cells. Airway ciliary cells express two subtypes of Ca 2+ –calmodulin‐dependent PDE1 (PDE1A and PDE1C; Bender & Beavo, ; Kogiso et al., , , ); PDE1A is expressed in both the cilia and the cell body, whereas PDE1C is expressed only in the cell body. PDE1A exists in the ODA‐regulating metabolon, but not the IDA‐regulating metabolon, in the cilium.…”

“…This PDE1A expressed in the CBF‐regulating metabolon causes the slower time course of the procaterol‐induced increase in CBF compared with CBA. Inhibition of PDE1A, caused by a reduction in [Ca 2+ ] i , hastens the time course of the procaterol‐induced increase in CBF by stimulating cAMP accumulation in the CBF‐regulating metabolon (Kogiso et al., ). These results suggest that interactions between the Ca 2+ signal and cAMP signal play roles in the maintenance of adequate ciliary beating.…”

“…The Ca 2+ and cAMP signals have been recognized independently to increase CBF in nasal ciliary cells (Smith et al., ). However, we have found that the Ca 2+ ‐dependent PDE1, PDE1A, regulates cAMP accumulation in airway ciliary cells (Kogiso et al., ).…”