Saori Tanaka

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

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 β2-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 Ca2+ concentration ([Ca2+]i) caused by switching to an EGTA-containing Ca2+-free solution from normal one elevated the procaterol-induced increasing rate of CBF. These observations suggest that Ca2+-dependent PDE1 controls cAMP-stimulated CBF increase. Either application of 8MmIBMX (8-methoxymethyl-IBMX, a selective PDE1 inhibitor), BAPTA-AM (an intracellular Ca2+ 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

What is the central question of this study? The ciliary beat frequency (CBF) of the airway is controlled by [Ca2+]i. However, the effects of a reduction in [Ca2+]i on CBF are still controversial (an increase, a decrease or no change). What is the main finding and its importance? This study demonstrated that [Ca2+]i directly regulates CBF (direct action) and also indirectly regulates CBF via cAMP accumulation controlled by Ca2+‐dependent PDE1 activity (indirect action). The final CBF is determined by the balance of direct and indirect actions. PDE1 plays crucial roles in the regulation of airway CBF.

PPARα induced NOS1 phosphorylation via PI3K/Akt in guinea pig antral mucous cells: NO-enhancement in Ca(2+)-regulated exocytosis.

A PPARα (peroxisome proliferation activation receptor α) agonist (GW7647) activates nitric oxide synthase 1 (NOS1) to produce NO leading to cGMP accumulation in antral mucous cells. In this study, we examined how PPARα activates NOS1. The NO production stimulated by GW7647 was suppressed by inhibitors of PI3K (wortmannin) and Akt (AKT 1/2 Kinase Inhibitor, AKT-inh), although it was also suppressed by the inhibitors of PPARα (GW6471) and NOS1 (N-PLA). GW7647 enhanced the ACh (acetylcholine)-stimulated exocytosis (Ca(2+)-regulated exocytosis) mediated via NO, which was abolished by GW6471, N-PLA, wortmannin, and AKT-inh. The Western blotting revealed that GW7647 phosphorylates NOS1 via phosphorylation of PI3K/Akt in antral mucous cells. The immunofluorescence examinations demonstrated that PPARα existing with NOS1 co-localizes with PI3K and Akt in the cytoplasm of antral mucous cells. ACh alone and AACOCF3, an analogue of arachidonic acid (AA), induced the NOS1 phosphorylation via PI3K/Akt to produce NO, which was inhibited by GW6471. Since AA is a natural ligand for PPARα, ACh stimulates PPARα probably via AA. In conclusion, PPARα activates NOS1 via PI3K/Akt phosphorylation to produce NO in antral mucous cells during ACh stimulation.

Seihai-to (TJ-90)-Induced Activation of Airway Ciliary Beatings of Mice: Ca2+ Modulation of cAMP-Stimulated Ciliary Beatings via PDE1

Sei-hai-to (TJ-90, Qing Fei Tang), a Chinese traditional medicine, increases ciliary beat frequency (CBF) and ciliary bend angle (CBA) mediated via cAMP (3′,5′-cyclic adenosine monophosphate) accumulation modulated by Ca2+-activated phosphodiesterase 1 (PDE1A). A high concentration of TJ-90 (≥40 μg/mL) induced two types of CBF increases, a transient increase (an initial increase, followed by a decrease) and a sustained increase without any decline, while it only sustained the CBA increase. Upon inhibiting increases in intracellular Ca2+ concentration ([Ca2+]i) by 10 μM BAPTA-AM (Ca2+-chelator, 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis(acetoxymethyl ester) or Ca2+/calmodulin-dependent PDE1 by 8MmIBMX (a selective PDE1 inhibitor), TJ-90 (400 μg/mL) induced only the sustained CBF increase without any transient CBF increase. The two types of the CBF increase (the transient increase and the sustained increase) induced by TJ-90 (≥40 μg/mL) were mimicked by the stimulation with both procaterol (100 pM) and ionomycin (500 nM). Thus, TJ-90 stimulates small increases in the intracellular cAMP concentration ([cAMP]i) and [Ca2+]i in airway ciliary cells of mice. These small increases in [cAMP]i and [Ca2+]i cause inducing a transient CBF increase or a sustained CBF increase in an airway ciliary cells, depending on the dominant signal, Ca2+-signal, or cAMP-signal.

PPARα autocrine regulation of Ca2+-regulated exocytosis in guinea pig antral mucous cells: NO and cGMP accumulation

In antral mucous cells, acetylcholine (ACh, 1 μM) activates Ca(2+)-regulated exocytosis, consisting of a peak in exocytotic events that declines rapidly (initial phase) followed by a second slower decline (late phase) lasting during ACh stimulation. GW7647 [a peroxisome proliferation activation receptor α (PPARα) agonist] enhanced the ACh-stimulated initial phase, and GW6471 (a PPARα antagonist) abolished the GW7647-induced enhancement. However, GW6471 produced the delayed, but transient, increase in the ACh-stimulated late phase, and it also decreased the initial phase and produced the delayed increase in the late phase during stimulation with ACh alone. A similar delayed increase in the ACh-stimulated late phase is induced by an inhibitor of the PKG, Rp8BrPETcGMPS, suggesting that GW6471 inhibits cGMP accumulation. An inhibitor of nitric oxide synthase 1 (NOS1), N(5)-[imino(propylamino)methyl]-L-ornithine hydrochloride (N-PLA), also abolished the GW7647-induced-enhancement of ACh-stimulated initial phase but produced the delayed increase in the late phase. However, in the presence of N-PLA, an NO donor or 8BrcGMP enhanced the ACh-stimulated initial phase and abolished the delayed increase in the late phase. Moreover, GW7647 and ACh stimulated NO production and cGMP accumulation in antral mucosae, which was inhibited by GW6471 or N-PLA. Western blotting and immunohistochemistry revealed that NOS1 and PPARα colocalize in antral mucous cells. In conclusion, during ACh stimulation, a PPARα autocrine mechanism, which accumulates NO via NOS1 leading to cGMP accumulation, modulates the Ca(2+)-regulated exocytosis in antral mucous cells.