PKA induces Ca2+ release and enhances ciliary beat frequency in a Ca2+-dependent and -independent manner

A 20:1 synergetic mixture of cafedrine/theodrenaline accelerates particle transport velocity in murine tracheal epithelium via IP3 receptor-associated calcium release

Background: Mucociliary clearance is a pivotal physiological mechanism that protects the lung by ridding the lower airways of pollution and colonization by pathogens, thereby preventing infections. The fixed 20:1 combination of cafedrine and theodrenaline has been used to treat perioperative hypotension or hypotensive states due to emergency situations since the 1960s. Because mucociliary clearance is impaired during mechanical ventilation and critical illness, the present study aimed to evaluate the influence of cafedrine/theodrenaline on mucociliary clearance. Material and Methods: The particle transport velocity (PTV) of murine trachea preparations was measured as a surrogate for mucociliary clearance under the influence of cafedrine/theodrenaline, cafedrine alone, and theodrenaline alone. Inhibitory substances were applied to elucidate relevant signal transduction cascades. Results: All three applications of the combination of cafedrine/theodrenaline, cafedrine alone, or theodrenaline alone induced a sharp increase in PTV in a concentration-dependent manner with median effective concentrations of 0.46 µM (consisting of 9.6 µM cafedrine and 0.46 µM theodrenaline), 408 and 4 μM, respectively. The signal transduction cascades were similar for the effects of both cafedrine and theodrenaline at the murine respiratory epithelium. While PTV remained at its baseline value after non-selective inhibition of β-adrenergic receptors and selective inhibition of β1 receptors, cafedrine/theodrenaline, cafedrine alone, or theodrenaline alone increased PTV despite the inhibition of the protein kinase A. However, IP3 receptor activation was found to be the pivotal mechanism leading to the increase in murine PTV, which was abolished when IP3 receptors were inhibited. Depleting intracellular calcium stores with caffeine confirmed calcium as another crucial messenger altering the PTV after the application of cafedrine/theodrenaline. Discussion: Cafedrine/theodrenaline, cafedrine alone, and theodrenaline alone exert their effects via IP3 receptor-associated calcium release that is ultimately triggered by β1-adrenergic receptor stimulation. Synergistic effects at the β1-adrenergic receptor are highly relevant to alter the PTV of the respiratory epithelium at clinically relevant concentrations. Further investigations are needed to assess the value of cafedrine/theodrenaline-mediated alterations in mucociliary function in clinical practice.

Effects of long-acting muscarinic antagonists on promoting ciliary function in airway epithelium

Background

Mucociliary clearance (MCC) is an essential defense mechanism in airway epithelia for removing pathogens from the respiratory tract. Impaired ciliary functions and MCC have been demonstrated in asthma and chronic obstructive pulmonary disease (COPD). Long-acting muscarinic antagonists (LAMAs) are a major class of inhaled bronchodilators, which are used for treating asthma and COPD; however, the effects of LAMAs on ciliary function remain unclear. This study aimed to identify the effects of LAMAs on airway ciliary functions.

Methods

Wild-type BALB/c mice were treated with daily intranasal administrations of glycopyrronium for 7 days, and tracheal samples were collected. Cilia-driven flow and ciliary activity, including ciliary beat frequency (CBF), ciliary beating amplitude, effective stroke velocity, recovery stroke velocity and the ratio of effective stroke velocity to recovery stroke velocity, were analyzed by imaging techniques. Using in vitro murine models, tracheal tissues were transiently cultured in media with/without LAMAs, glycopyrronium or tiotropium, for 60 min. Cilia-driven flow and ciliary activity were then analyzed. Well-differentiated normal human bronchial epithelial (NHBE) cells were treated with glycopyrronium, tiotropium, or vehicle for 60 min, and CBF was evaluated. Several mechanistic analyses were performed.

Results

Intranasal glycopyrronium administration for 7 days significantly increased cilia-driven flow and ciliary activity in murine airway epithelium. In the murine tracheal organ culture models, treatment with glycopyrronium or tiotropium for 60 min significantly increased cilia-driven flow and ciliary activity in airway epithelium. Further, we confirmed that 60-min treatment with glycopyrronium or tiotropium directly increased CBF in well-differentiated NHBE cells. In the mechanistic analyses, neither treatment with glycopyrronium nor tiotropium affected intracellular calcium ion concentrations in well-differentiated NHBE cells. Glycopyrronium did not increase protein kinase A activity in well-differentiated NHBE cells. Moreover, glycopyrronium had no effect on extracellular adenosine triphosphate concentration.

Conclusions

LAMAs exert a direct effect on airway epithelium to enhance ciliary function, which may improve impaired MCC in asthma and COPD. Further investigations are warranted to elucidate the underlying mechanisms of the effects of LAMAs on the promotion of airway ciliary function.

Reversal of Chronic Rhinosinusitis-Associated Sinonasal Ciliary Dysfunction

Background

Although multiple etiologies contribute to the development of chronic rhinosinusitis (CRS), a common pathophysiological sequelae is ineffective sinonasal mucociliary clearance, leading to stasis of sinonasal secretions, with subsequent infection and/or persistent inflammation. Proper therapeutic intervention typically restores mucociliary activity, suggesting that the pathophysiological process(es) responsible for CRS-associated mucostasis may be reversible. We previously demonstrated a blunted response of CRS sinonasal cilia after purinergic stimulation. This study investigated whether the blunted ciliary response is unique to purinergic stimulation and addressed whether the blunted effect is primarily caused by local CRS-associated mediators or inherent genetic defects in ciliary function.

Methods

A dual temperature-controlled perfusion chamber, differential interference contrast microscopy, and high-speed digital video were used to analyze both basal as well as cholinergic, adrenergic, and purinergic stimulation of cilia in human sinonasal mucosal explants. Additionally, enzymically dissociated sinonasal ciliated cells were maintained ex vivo in submersion, on glass coverslips, and assessed daily for purinergic ciliary beat frequency stimulation.

Results

Cholinergic and adrenergic stimulation generally were blunted in mucosal explants obtained from CRS patients. Ex vivo maintenance of samples demonstrated that the majority of CRS samples developed a stimulatory phenotype within 36 hours of culturing.

Conclusion

CRS is a common debilitating disease principally affecting sinonasal epithelial function with a resultant diminution of mucociliary transport. Presently, little is known about how this disease process affects the sinonasal epithelial ciliated cells. Our data suggest that ciliary response to environmental insults is blunted in a reversible manner in CRS patients.

Calumenin contributes to ER-Ca2+ homeostasis in bronchial epithelial cells expressing WT and F508del mutated CFTR and to F508del-CFTR retention

Cystic Fibrosis (CF) is the most frequent fatal genetic disease in Caucasian populations. Mutations in the chloride channel CF Transmembrane Conductance Regulator (CFTR) gene are responsible for functional defects of the protein and multiple associated dysregulations. The most common mutation in patients with CF, F508del-CFTR, causes defective CFTR protein folding. Thus minimal levels of the receptor are expressed at the cell surface as the mutated CFTR is retained in the endoplasmic reticulum (ER) where it correlates with defective calcium (Ca²⁺) homeostasis. In this study, we discovered that the Ca²⁺ binding protein Calumenin (CALU) is a key regulator in the maintenance of ER-Ca²⁺ calcium homeostasis in both wild type and F508del-CFTR expressing cells. Calumenin modulates SERCA pump activity without drastically affecting ER-Ca²⁺ concentration. In addition, reducing Calumenin expression in CF cells results in a partial restoration of CFTR activity, highlighting a potential function of Calumenin in CFTR maturation. These findings demonstrate a pivotal role for Calumenin in CF cells, providing insights into how modulation of Calumenin expression or activity may be used as a potential therapeutic tool to correct defects in F508del-CFTR.

Marked increases in mucociliary clearance produced by synergistic secretory agonists or inhibition of the epithelial sodium channel

Mucociliary clearance (MCC) is a critical host innate defense mechanism in airways, and it is impaired in cystic fibrosis (CF) and other obstructive lung diseases. Epithelial fluid secretion and absorption modify MCC velocity (MCCV). We tested the hypotheses that inhibiting fluid absorption accelerates MCCV, whereas inhibiting fluid secretion decelerates it. In airways, ENaC is mainly responsible for fluid absorption, while anion channels, including CFTR and Ca²⁺-activated chloride channels mediate anion/fluid secretion. MCCV was increased by the cAMP-elevating agonists, forskolin or isoproterenol (10 μM) and by the Ca²⁺-elevating agonist, carbachol (0.3 μM). The CFTR-selective inhibitor, CFTR_inh-172, modestly reduced MCCV-increases induced by forskolin or isoproterenol but not increases induced by carbachol. The ENaC inhibitor benzamil increased basal MCCV as well as MCCV increases produced by forskolin or carbachol. MCC velocity was most dramatically accelerated by the synergistic combination of forskolin and carbachol, which produced near-maximal clearance rates regardless of prior treatment with CFTR or ENaC inhibitors. In CF airways, where CFTR-mediated secretion (and possibly synergistic MCC) is lost, ENaC inhibition via exogenous agents may provide therapeutic benefit, as has long been proposed.

Airway Epithelial Cell Release of GABA is Regulated by Protein Kinase A

INTRODUCTION

γ-amino butyric acid (GABA) is not only the major inhibitory neurotransmitter in the central nervous system (CNS), but it also plays an important role in the lung, mediating airway smooth muscle relaxation and mucus production. As kinases such as protein kinase A (PKA) are known to regulate the release and reuptake of GABA in the CNS by GABA transporters, we hypothesized that β-agonists would affect GABA release from airway epithelial cells through activation of PKA.

METHODS

C57/BL6 mice received a pretreatment of a β-agonist or vehicle (PBS), followed by methacholine or PBS. Bronchoalveolar lavage (BAL) was collected and the amount of GABA was quantified using HPLC mass spectrometry. For in vitro studies, cultured BEAS-2B human airway epithelial cells were loaded with (3)H-GABA. (3)H-GABA released was measured during activation and inhibition of PKA and tyrosine kinase signaling pathways.

RESULTS

β-agonist pretreatment prior to methacholine challenge attenuated in vivo GABA release in mouse BAL and (3)H-GABA release from depolarized BEAS-2B cells. GABA release was also decreased in BEAS-2B cells by increases in cAMP but not by Epac or tyrosine kinase activation.

CONCLUSION

β-agonists decrease GABA release from airway epithelium through the activation of cAMP and PKA. This has important therapeutic implications as β-agonists and GABA are important mediators of both mucus production and airway smooth muscle tone.

SERCA and PMCA pumps contribute to the deregulation of Ca2+ homeostasis in human CF epithelial cells

Cystic Fibrosis (CF) disease is caused by mutations in the CFTR gene (CF transmembrane conductance regulator). F508 deletion is the most represented mutation, and F508del-CFTR is absent of plasma membrane and accumulates into the endoplasmic reticulum (ER) compartment. Using specific Ca2+ genetics cameleon probes, we showed in the human bronchial CF epithelial cell line CFBE that ER Ca2+ concentration was strongly increased compared to non-CF (16HBE) cells, and normalized by the F508del-CFTR corrector agent, VX-809. We also showed that ER F508del-CFTR retention increases SERCA (Sarcoplasmic/Reticulum Ca2+ ATPase) pump activity whereas PMCA (Plasma Membrane Ca2+ ATPase) activities were reduced in these CF cells compared to corrected CF cells (VX-809) and non-CF cells. We are showing for the first time CFTR/SERCA and CFTR/PMCA interactions that are modulated in CF cells and could explain part of Ca2+ homeostasis deregulation due to mislocalization of F508del-CFTR. Using ER or mitochondria genetics Ca2+ probes, we are showing that ER Ca2+ content, mitochondrial Ca2+ uptake, SERCA and PMCA pump, activities are strongly affected by the localization of F508del-CFTR protein.

Mucociliary clearance and submucosal gland secretion in the ex vivo ferret trachea

In many species submucosal glands are an important source of tracheal mucus, but the extent to which mucociliary clearance (MCC) depends on gland secretion is unknown. To explore this relationship, we measured basal and agonist-stimulated MCC velocities in ex vivo tracheas from adult ferrets and compared the velocities with previously measured rates of ferret glandular mucus secretion (Cho HJ, Joo NS, Wine JJ. Am J Physiol Lung Cell Mol Physiol 299: L124-L136, 2010). Stimulated MCC velocities (mm/min, means ± SE for 10- to 35-min period poststimulation) were as follows: 1 μM carbachol: 19.1 ± 3.3 > 10 μM phenylephrine: 15.3 ± 2.4 ≈ 10 μM isoproterenol: 15.0 ± 1.9 ≈ 10 μM forskolin: 14.6 ± 3.1 > 1 μM vasoactive intestinal peptide (VIP): 10.2 ± 2.2 >> basal (t15): 1.8 ± 0.3; n = 5-10 for each condition. Synergistic stimulation of MCC was observed between low concentrations of carbachol (100 nM) and isoproterenol (300 nM). Bumetanide inhibited carbachol-stimulated MCC by ~70% and abolished the increase in MCC stimulated by forskolin + VIP, whereas HCO3 (-)-free solutions did not significantly inhibit MCC to either intracellular Ca(2+) concentration or intracellular cAMP concentration ([cAMP]i)-elevating agonists. Stimulation and inhibition of MCC and gland secretion differed in several respects: most importantly, elevating [cAMP]i increased MCC much more effectively than expected from its effects on gland secretion, and bumetanide almost completely inhibited [cAMP]i-stimulated MCC while it had a smaller effect on gland secretion. We conclude that changes in glandular fluid secretion are complexly related to MCC and discuss possible reasons for this.

Control of ventricular ciliary beating by the melanin concentrating hormone-expressing neurons of the lateral hypothalamus: a functional imaging survey

The cyclic peptide Melanin Concentrating Hormone (MCH) is known to control a large number of brain functions in mammals such as food intake and metabolism, stress response, anxiety, sleep/wake cycle, memory, and reward. Based on neuro-anatomical and electrophysiological studies these functions were attributed to neuronal circuits expressing MCHR1, the single MCH receptor in rodents. In complement to our recently published work (1) we provided here new data regarding the action of MCH on ependymocytes in the mouse brain. First, we establish that MCHR1 mRNA is expressed in the ependymal cells of the third ventricle epithelium. Second, we demonstrated a tonic control of MCH-expressing neurons on ependymal cilia beat frequency using in vitro optogenics. Finally, we performed in vivo measurements of CSF flow using fluorescent micro-beads in wild-type and MCHR1-knockout mice. Collectively, our results demonstrated that MCH-expressing neurons modulate ciliary beating of ependymal cells at the third ventricle and could contribute to maintain cerebro-spinal fluid homeostasis.

Molecular modulation of airway epithelial ciliary response to sneezing

Our purpose was to evaluate the effect of the mechanical force of a sneeze on sinonasal cilia function and determine the molecular mechanism responsible for eliciting the ciliary response to a sneeze. A novel model was developed to deliver a stimulation simulating a sneeze (55 mmHg for 50 ms) at 26°C to the apical surface of mouse and human nasal epithelial cells. Ciliary beating was visualized, and changes in ciliary beat frequency (CBF) were determined. To interrogate the molecular cascades driving sneeze-induced changes of CBF, pharmacologic manipulation of intra- and extracellular calcium, purinergic, PKA, and nitric oxide (NO) signaling were performed. CBF rapidly increases by ≥150% in response to a sneeze, which is dependent on the release of adenosine triphosphate (ATP), calcium influx, and PKA activation. Furthermore, apical release of ATP is independent of calcium influx, but calcium influx and subsequent increase in CBF are dependent on the ATP release. Lastly, we observed a blunted ciliary response in surgical specimens derived from patients with chronic rhinosinusitis compared to control patients. Apical ATP release with subsequent calcium mobilization and PKA activation are involved in sinonasal ciliary response to sneezing, which is blunted in patients with upper-airway disease.

CFTR and Ca Signaling in Cystic Fibrosis

Among the diverse physiological functions exerted by calcium signaling in living cells, its role in the regulation of protein biogenesis and trafficking remains incompletely understood. In cystic fibrosis (CF) disease the most common CF transmembrane conductance regulator (CFTR) mutation, F508del-CFTR generates a misprocessed protein that is abnormally retained in the endoplasmic reticulum (ER) compartment, rapidly degraded by the ubiquitin/proteasome pathway and hence absent at the plasma membrane of CF epithelial cells. Recent studies have demonstrated that intracellular calcium signals consequent to activation of apical G-protein-coupled receptors by different agonists are increased in CF airway epithelia. Moreover, the regulation of various intracellular calcium storage compartments, such as ER is also abnormal in CF cells. Although the molecular mechanism at the origin of this increase remains puzzling in epithelial cells, the F508del-CFTR mutation is proposed to be the onset of abnormal Ca²⁺ influx linking the calcium signaling to CFTR pathobiology. This article reviews the relationships between CFTR and calcium signaling in the context of the genetic disease CF.

Ciliary beat co-ordination by calcium

Motile cilia in the airway epithelium are the engine for mucociliary clearance, the mechanism responsible for cleaning the airways from inhaled particles. Human airway epithelial cilia appear to have a slow constitutive rate of beating, driven by inherent and spontaneous dynein ATPase activity. Additionally, cilia can increase their beating frequency by activation of several different control mechanisms. One of these controllers is calcium. Its intracellular concentration is regulated by purinergic and acetylcholine receptors. Besides the rate regulatory effect of calcium on ciliary beat, calcium is also involved in synchronizing the beat among cilia of one single cell as well as between cilia on different cells. This article gives an overview of the complex effects of calcium on the beating of motile cilia in the airways.

Cilia dysfunction

Cilia are complex and powerful cellular structures that serve a multitude of functions across many types of organisms. In humans, one of the most critical roles of cilia is defense of the airway. The respiratory epithelium is lined with cilia that normally carry out an integrated and coordinated mechanism called mucociliary clearance. Mucociliary clearance, the process by which cilia transport the viscous mucus blanket of the upper airway to the gastrointestinal tract, is the primary means by which the upper airway clears itself of pathogens, allergens, debris, and toxins. The complex structure and regulatory mechanisms that dictate the form and function of normal cilia are not entirely understood, but it is clear that ciliary dysfunction results in impaired respiratory defense. Ciliary dysfunction may be primary, the result of genetic mutations resulting in abnormal cilia structure, or secondary, the result of environmental, infectious or inflammatory stimuli that disrupt normal motility or coordination.

Misoprostol elevates intracellular calcium in Neuro-2a cells via protein kinase A

Misoprostol, a prostaglandin type E analogue, has been implicated in a number of neurodevelopmental disorders. However, its mode of action in the nervous system is not well understood. Misoprostol acts on the same receptors as prostaglandin E(2) (PGE(2)), a natural lipid-derived compound, which mediates important physiological functions in the nervous system via activation of four EP receptors (EP1-4). In this study we use a ratiometric calcium imaging with fura-2 AM as a calcium indicator to show that misoprostol alters intracellular calcium levels in mouse neuroblastoma (Neuro-2a) cells via similar mechanisms as PGE(2). We demonstrate that the misoprostol-induced increase in calcium is mediated by a protein kinase A (PKA)-dependent mechanism and that the EP4 receptor signaling pathway may play an inhibitory role on calcium regulation. Overall, this study provides further support for the involvement of PGE(2) signaling in calcium homeostasis and suggests its important role in the nervous system.

Adrenomedullin regulates sperm motility and oviductal ciliary beat via cyclic adenosine 5'-monophosphate/protein kinase A and nitric oxide

Cilium and flagellum beating are important in reproduction and defects in their motion are associated with ectopic pregnancy and infertility. Adrenomedullin (ADM) is a polypeptide present in the reproductive system. This report demonstrates a novel action of ADM in enhancing the flagellar/ciliary beating of human spermatozoa and rat oviductal ciliated cells. At the concentration found in the seminal plasma, it increases the progressive motility of spermatozoa. ADM binds to its classical receptor, calcitonin receptor-like receptor/receptor activity-modifying protein complex on spermatozoa. ADM treatment increases the protein kinase A activities, the cyclic adenosine monophosphate, and nitric oxide levels of spermatozoa and oviductal cells. Pharmacological activators and inhibitors confirmed that the ADM-induced flagella/ciliary beating was protein kinase A dependent. Whereas nitric oxide donors had no effect on sperm motility, they potentiated the motility-inducing action of protein kinase A activators, demonstrating for the first time the synergistic action of nitric oxide and protein kinase A signaling in flagellar/ciliary beating. The ADM-induced motility enhancement effect in spermatozoa also depended on the up-regulation of intracellular calcium, a known key regulator of sperm motility and ciliary beating. In conclusion, ADM is a common activator of flagellar/ciliary beating. The study provides a physiological basis on possible use of ADM as a fertility regulation drug.

Epithelium, cilia, and mucus: their importance in chronic rhinosinusitis

Chronic rhinosinusitis is a common disease resulting from inflammation of the sinonasal mucosa. It has long been recognized that patients with chronic rhinosinusitis have impaired capacity to clear sinonasal secretions. However, the cause of this pathologic process is not well understood. In this article the components of mucociliary clearance, including cilia, mucus production, and cilia beat frequency, are reviewed and alterations of the system discussed regarding contribution to the disease process.

Effect of cyclic AMP-elevating agents on airway ciliary beat frequency in central and lateral airways in rat precision-cut lung slices

In patients with chronic obstructive pulmonary disease (COPD), mucociliary clearance of the respiratory tract is impaired due to enhanced mucus secretion and deterioration of normal ciliary activity. We investigated the effects of cyclic AMP-elevating agents with a different mode of action on ciliary beat frequency (CBF) in rat large central and small lateral airways by comparing the phosphodiesterase-4 (PDE4) inhibitors rolipram and roflumilast to the beta(2)-adrenoceptor agonist terbutaline and the adenylyl cyclase activator forskolin. Rat precision-cut lung slices were prepared and effects of cyclic AMP-elevating agents on CBF were assessed for up to 4h. In central airways a time- and concentration-dependent increase in CBF was seen for roflumilast (59+/-4%, 1microM, 60min), rolipram (55+/-4%, 1microM, 60min), terbutaline (64+/-8%, 10microM, 60min) and forskolin (55+/-8%, 100microM, 60min). Only roflumilast and rolipram increased CBF in lateral airways, with a similar time course and maximum efficacy (roflumilast 48+/-5%, rolipram 54+/-2%). Incubation of lateral airways with terbutaline (10microM, +11%) or forskolin (100microM, +1%) had negligible effects. As a major novel finding this study reveals that PDE4 inhibitors increased CBF in central as well as in lateral airways, while terbutaline and forskolin affected CBF in proximal airways only.

Efficient mucociliary transport relies on efficient regulation of ciliary beating

The respiratory mucociliary epithelium is a synchronized and highly effective waste-disposal system. It uses mucus as a vehicle, driven by beating cilia, to transport unwanted particles, trapped in the mucus, away from the respiratory system. The ciliary machinery can function in at least two different modes: a low rate of beating that requires only ATP, and a high rate of beating regulated by second messengers. The mucus propelling velocity is linearly dependent on ciliary beat frequency (CBF). The linear dependence implies that a substantial increase in transport efficiency requires an equally substantial rise in CBF. The ability to enhance beating in response to various physiological cues is a hallmark of mucociliary cells. An intricate signaling network controls ciliary activity, which relies on interplay between calcium and cyclic nucleotide pathways.

Transient receptor potential vanilloid type 4 channel expression in chronic rhinosinusitis

BACKGROUND

Transient receptor potential (TRP) channels are a novel class of nonvoltage gated membrane cation channels that can be activated by mechanical stimulation and temperature change. Recently, TRP vanilloid type 4 (TRPV4) has been implicated in detecting viscosity changes in fallopian tube epithelial cells and inducing a compensatory response in ciliary activity and, as such, represents a possible molecular trigger for modulating respiratory ciliary activity. Thus, the goal of this study was to establish the expression pattern of TRPV4 in human sinonasal mucosa and determine whether expression is altered in chronic rhinosinusitis (CRS).

METHODS

Sinus mucosal biopsy specimens were obtained from patients with CRS, CRS with nasal polyps (NPs), and healthy controls. TRPV4 mRNA and protein expression were confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblot analysis, respectively. TRPV4 gene expression was measured next using quantitative RT-PCR. Immunofluorescence was performed on sinus mucosal explants and respiratory epithelial air-liquid interface cultures to localize cellular expression.

RESULTS

TRPV4 mRNA and protein were expressed in all samples. There was a statistically significant increase (p < 0.05) in TRPV4 gene expression in nonpolypoid CRS patients, but no difference in CRS with NP. Dual label immunofluorescence showed TRPV4 expression to be mutually exclusive of ciliated cells.

CONCLUSION

Although TRPV4 represents an ideal molecular trigger for ciliary modulation, absent expression of the channel in ciliated cells precludes this function. However, altered expression of the channel in CRS and presumed expression of TRPV4 in secretory cells of the mucosa indicate a potential role in mucus homeostasis and CRS pathogenesis.

Localized cytosolic alkalization and its functional impact in ciliary cells

Using confocal microscopy we demonstrate that ciliary cells from airway epithelium maintain two qualitatively distinct cytosolic regions in terms of pH regulation. While the bulk of the cytosol is stringently buffered and is virtually insensitive to changes in extracellular pH (pHo), the values of cytosolic pH in the vicinity of the ciliary membrane is largely determined by pHo. Variation of pHo from 6.2 up to 8.5 failed to affect ciliary beat frequency (CBF). Application of NH(4)Cl induced profound localized alkalization near cilia, which did not depress ciliary activity, but resulted in strong and prolonged enhancement of CBF. Calmodulin and protein kinase A (PKA) functionality was essential for the alkalization-induced CBF enhancement. We suggest that the ability of airway epithelium to sustain unusually strong but localized cytosolic alkalization near cilia facilitates CBF enhancement through altering the binding constants of Ca2+ to calmodulin and promotion of Ca2+-calmodulin complex formation. The NH4Cl-induced elevations in cytosolic pH and Ca2+ concentration act synergistically to activate calmodulin-dependent processes, cAMP pathway, and, thereby, stimulate CBF.

Involvement of Ca2+- and cyclic adenosine monophosphate-mediated signaling pathways in photodynamic injury of isolated crayfish neuron and satellite glial cells

To investigate the mechanisms of oxidative injury of neurons and glia, we studied the photodynamic effect on isolated stretch receptor that consists of only two sensory neurons enwrapped by satellite glial cells. Photodynamic therapy (PDT), a potent inducer of oxidative stress, is a prospective method for destruction of brain tumors. PDT induced functional inactivation and necrosis of neurons, necrosis, apoptosis, and proliferation of glial cells. The roles of calmodulin, calmodulin-dependent kinase II, phospholipase C, protein kinases A and C, and phosphodiesterase in these processes were studied by using their inhibitors: fluphenazine, KN-93, D-609, H89, staurosporine, and papaverine, respectively. PDT-induced firing abolishment was enhanced by H89 or papaverine, whereas staurosporine acted oppositely. Fluphenazine or KN-93 reduced necrosis of neurons and glial cells. H89 enhanced necrosis of neurons, whereas staurosporine enhanced necrosis of glial cells. Inhibition of protein kinases A and C enhanced PDT-induced glial apoptosis. Photodynamic gliosis was prevented by KN-93 or staurosporine. These data indicate possible involvement of calmodulin and calmodulin-dependent kinase II in photoinduced necrosis of neurons and glia. Protein kinase C could protect glial cells from necrosis and apoptosis and participate in photoinduced gliosis and loss of neuronal activity. Protein kinase A maintained neuronal firing and protected neurons from photoinduced necrosis and glial cells from apoptosis. Phosphodiesterase reduced necrosis of photosensitized neurons and glia. Thus, Ca(2+)- and cAMP-mediated signaling pathways were involved in photooxidative injury of neurons and glia. Their pharmacological modulation may differently change the efficacy of photodynamic injury of neurons and glial cells.

The effect of endogenous nitric oxide on mechanical ciliostimulation of human nasal mucosa

BACKGROUND

Endogenous nitric oxide (NO) production by the inducible NO-synthase is enhanced in the nasal respiratory epithelium of patients with allergic rhinitis. Recent experimental data suggest endogenous NO to be strongly involved in the regulation of ciliary activity, the driving force of the mucociliary transport system.

OBJECTIVE

In this study, we investigated the effect of endogenous NO on mechanical stimulation of ciliary activity in a nasal mucosa explant model.

METHODS

Cultures of nasal mucosa explants were incubated with TNF-alpha and bacterial lipopolysaccharides (LPS) to enhance endogenous NO production. Direct in vitro NO imaging was performed by the fluorescent NO-indicator DAF-2 DA and laser scanning confocal microscopy. Ciliary beat frequency (CBF) was determined using a photoelectric technique. Mechanical stimulation was performed by two consecutive flow increments in a closed perfusion chamber. Endogenous NO-synthesis was blocked by l-NAME before the second flow stimulation.

RESULTS

Under control conditions the mean rise of CBF relative to baseline was 30.2% during the first flow increment and 30.7% during the second flow increment. Blocking of the endogenous NO synthesis in TNF-alpha/LPS-stimulated cultures reduced baseline CBF by 10.6+/-2.1% (P<0.05) but the effect of mechanical ciliostimulation on CBF remained unchanged (36.0% vs. 38.2%).

CONCLUSION

In conclusion, endogenous NO- and Ca(2+)-dependent mechanical stimulation of ciliary activity probably use independent intracellular signalling pathways. The combination of both effects on ciliary activity is likely to improve the local defence against inhaled allergens in patients with nasal allergies.

Nervous control of ciliary beating by Cl-, Ca2+ and calmodulin inTritonia diomedea

In vertebrates, motile cilia line airways, oviducts and ventricles. Invertebrate cilia often control feeding, swimming and crawling, or gliding. Yet control and coordination of ciliary beating remains poorly understood. Evidence from the nudibranch mollusc, Tritonia diomedea, suggests that locomotory ciliated epithelial cells may be under direct electrical control. Here we report that depolarization of ciliated pedal epithelial (CPE)cells increases ciliary beating frequency (CBF), and elicits CBF increases similar to those caused by dopamine and the neuropeptide, TPep-NLS. Further,four CBF stimulants (zero external Cl-, depolarization, dopamine and TPep-NLS) depend on a common mode of action, viz. Ca2+influx, possibly through voltage-gated Ca2+ channels, and can be blocked by nifedipine. Ca2+ influx alone, however, does not provide all the internal Ca2+ necessary for CBF change. Ryanodine receptor(RyR) channel-gated internal stores are also necessary for CBF excitation. Caffeine can stimulate CBF and is sensitive to the presence of the RyR blocker dantrolene. Dantrolene also reduces CBF excitation induced by dopamine and TPep-NLS. Finally, W-7 and calmidazolium both block CBF excitation by caffeine and dopamine, and W-7 is effective at blocking TPep-NLS excitation. The effects of calmidazolium and W-7 suggest a role for Ca2+-calmodulin in regulating CBF, either directly or via Ca2+-calmodulin dependent kinases or phosphodiesterases. From these results we hypothesize dopamine and TPep-NLS induce depolarization-driven Ca2+ influx and Ca2+ release from internal stores that activates Ca2+-calmodulin, thereby increasing CBF.

Both cAMP and cGMP are required for maximal ciliary beat stimulation in a cell-free model of bovine ciliary axonemes

Previously, we have shown that the ATPase-dependent motion of cilia in bovine bronchial epithelial cells (BBEC) can be regulated through the cyclic nucleotides, cAMP via the cAMP-dependent protein kinase (PKA) and cGMP via the cGMP-dependent protein kinase (PKG). Both cyclic nucleotides cause an increase in cilia beat frequency (CBF). We hypothesized that cAMP and cGMP may act directly at the level of the ciliary axoneme in BBEC. To examine this, we employed a novel cell-free system utilizing detergent-extracted axonemes. Axoneme movement was whole-field analyzed digitally with the Sisson-Ammons video analysis system. A suspension of extracted axonemes remains motionless until the addition of 1 mM ATP that establishes a baseline CBF similar to that seen when analyzing intact ciliated BBEC. Adding 10 microM cAMP or 10 microM cGMP increases CBF beyond the established ATP baseline. However, the cyclic nucleotides did not stimulate CBF in the absence of ATP. Therefore, the combination of cAMP and cGMP augments ATP-driven CBF increases at the level of isolated axoneme.

Intracellular Ca2+ regulates the phosphorylation and the dephosphorylation of ciliary proteins via the NO pathway

The phosphorylation profile of ciliary proteins under basal conditions and after stimulation by extracellular ATP was investigated in intact tissue and in isolated cilia from porcine airway epithelium using anti-phosphoserine and anti-phosphothreonine specific antibodies. In intact tissue, several polypeptides were serine phosphorylated in the absence of any treatment (control conditions). After stimulation by extracellular ATP, changes in the phosphorylation pattern were detected on seven ciliary polypeptides. Serine phosphorylation was enhanced for three polypeptides (27, 37, and 44 kD), while serine phosphorylation was reduced for four polypeptides (35, 69, 100, and 130 kD). Raising intracellular Ca²⁺ with ionomycin induced identical changes in the protein phosphorylation profile. Inhibition of the NO pathway by inhibiting either NO syntase (NOS), guanylyl cyclase (GC), or cGMP-dependent protein kinase (PKG) abolished the changes in phosphorylation induced by ATP. The presence of PKG within the axoneme was demonstrated using a specific antibody. In addition, in isolated permeabilized cilia, submicromolar concentrations of cGMP induced protein phosphorylation. Taken together, these results suggest that the axoneme is an integral part of the intracellular NO pathway. The surprising observation that ciliary activation is accompanied by sustained dephosphorylation of ciliary proteins via NO pathway was not detected in isolated cilia, suggesting that the protein phosphatases were either lost or deactivated during the isolation procedure. This work reveals that any pharmacological manipulation that abolished phosphorylation and dephosphorylation also abolished the enhancement of ciliary beating. Thus, part or all of the phosphorylated polypeptides are likely directly involved in axonemal regulation of ciliary beating.

Plasma and intracellular membrane inositol 1,4,5-trisphosphate receptors mediate the Ca(2+) increase associated with the ATP-induced increase in ciliary beat frequency

An increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) has been shown to be involved in the increase in ciliary beat frequency (CBF) in response to ATP; however, the signaling pathways associated with inositol 1,4,5-trisphosphate (IP(3)) receptor-dependent Ca(2+) mobilization remain unresolved. Using radioimmunoassay techniques, we have demonstrated the appearance of two IP(3) peaks occurring 10 and 60 s after ATP addition, which was strongly correlated with a release of intracellular Ca(2+) from internal stores and an influx of extracellular Ca(2+), respectively. In addition, ATP-dependent Ca(2+) mobilization required protein kinase C (PKC) and Ca(2+)/calmodulin-dependent protein kinase II activation. We found an increase in PKC activity in response to ATP, with a peak at 60 s after ATP addition. Xestospongin C, an IP(3) receptor blocker, significantly diminished both the ATP-induced increase in CBF and the initial transient [Ca(2+)](i) component. ATP addition in the presence of xestospongin C or thapsigargin revealed that the Ca(2+) influx is also dependent on IP(3) receptor activation. Immunofluorescence and confocal microscopic studies showed the presence of IP(3) receptor types 1 and 3 in cultured ciliated cells. Immunogold electron microscopy localized IP(3) receptor type 3 to the nucleus, the endoplasmic reticulum, and, interestingly, the plasma membrane. In contrast, IP(3) receptor type 1 was found exclusively in the nucleus and the endoplasmic reticulum. Our study demonstrates for the first time the presence of IP(3) receptor type 3 in the plasma membrane in ciliated cells and leads us to postulate that the IP(3) receptor can directly trigger Ca(2+) influx in response to ATP.

Effect of serotonin on ciliary beating and intracellular calcium concentration in identified populations of embryonic ciliary cells

Embryos of the pond snail Helisoma trivolvis express three known subtypes of ciliary cells on the surface of the embryo early in development:pedal, dorsolateral and scattered single ciliary cells (SSCCs). The pedal and dorsolateral ciliary cells are innervated by a pair of serotonergic sensory-motor neurons and are responsible for generating the earliest whole-animal behavior, rotation within the egg capsule. Previous cell culture studies on unidentified ciliary cells revealed that serotonin(5-hydroxytryptamine; 5-HT) produces a significant increase in the ciliary beat frequency (CBF) in a large proportion of ciliary cells. Both Ca2+ influx and a unique isoform of protein kinase C (PKC) were implicated in the signal transduction pathway underlying the cilio-excitatory response to 5-HT. The goal of the present study was to characterize the anatomical and physiological differences between the three known populations of superficial ciliary cells. The pedal and dorsolateral ciliary cells shared common structural characteristics, including flat morphology, dense cilia and lateral accessory ciliary rootlets. By contrast, the SSCCs had a cuboidal morphology, reduced number of cilia, increased ciliary length and absence of lateral accessory rootlets. In cultures containing unidentified ciliary cells,the calcium/calmodulin-dependent enzyme inhibitor calmidazolium (2 μmol l–1) blocked the stimulatory effect of 5-HT (100 μmol l–1) on CBF. In addition, 50% of unidentified cultured cells responded to 5-HT (100 μmol l–1) with an increase in[Ca2+]i. To facilitate the functional analyses of the individual populations, we developed a method to culture identified ciliary subtypes and characterized their ciliary and calcium responses to 5-HT. In cultures containing either pedal or dorsolateral ciliary cells, 5-HT (100μmol l–1) produced a rapid increase in CBF and a slower increase in [Ca2+]i in all cells examined. By contrast,the CBF and [Ca2+]i of SSCCs were not affected by 100μmol l–1 5-HT. Immunohistochemistry for two putative 5-HT receptors recently cloned from Helisoma revealed that pedal and dorsolateral ciliary cells consistently express the 5-HT1Helprotein. Intense 5-HT7Hel immunoreactivity was observed in only a subset of pedal and dorsolateral ciliary cells. Cells neighboring the SSCCs,but not the ciliary cells themselves, expressed 5-HT1Hel and 5-HT7Hel immunoreactivity. These data suggest that the pedal and dorsolateral ciliary cells, but not the SSCCs are a homogeneous physiological subtype that will be useful for elucidating the signal transduction mechanisms underlying 5-HT induced cilio-excitation.

The role of cGMP in the regulation of rabbit airway ciliary beat frequency

The involvement of cyclic guanosine 3',5'-monophosphate (cGMP) and cGMP-dependent protein kinase (PKG) and their interaction with the Ca2+-dependent mechanisms in the regulation of ciliary activity are not well understood. To investigate how cGMP regulates ciliary activity, changes in ciliary beat frequency (CBF) and intracellular calcium concentration ([Ca2+]i) of rabbit tracheal ciliated cells in response to 8-bromo-cGMP (Br-cGMP) were simultaneously quantified using digital, high-speed phase-contrast and fluorescence imaging. Br-cGMP induced a response in ciliary activity that could be separated into two parts. Firstly, Br-cGMP induced a concentration-dependent increase in the basal CBF that occurred without increasing the [Ca2+]i. This response was not affected by excessively buffering the [Ca2+]i with BAPTA but was abolished by KT5823, a PKG inhibitor. Secondly, Br-cGMP induced a series of transient increases in CBF that were superimposed on the sustained increases in CBF. These transient increases in CBF correlated with the stimulation of a series of transient increases in [Ca2+]i and were abolished by BAPTA, but were unaffected by KT5823. The magnitude of the transient increases in CBF and [Ca2+]i were not dependent on the concentration of Br-cGMP. The Ca2+-dependent changes in CBF induced by ionomycin or ATP were not affected by KT5823. From these results, we propose that cGMP increases CBF in two ways: firstly through a Ca2+-independent mechanism involving PKG, and secondly through a Ca2+-dependent mechanism following the stimulation of changes in [Ca2+]i. In addition, we suggest that the Ca2+-dependent stimulation of rabbit airway ciliary activity does not initially require PKG activation.

Constitutive and permissive roles of nitric oxide activity in embryonic ciliary cells

Embryos of Helisoma trivolvis exhibit cilia-driven rotation within the egg capsule during development. In this study we examined whether nitric oxide (NO) is a physiological regulator of ciliary beating in cultured ciliary cells. The NO donor S-nitroso-N-acetylpenicillamine (SNAP; 1-1,000 microM) produced a dose-dependent increase in ciliary beat frequency (CBF). In contrast, the nitric oxide synthase (NOS) inhibitor 7-nitroindazole (10 and 100 microM) inhibited the basal CBF and blocked the stimulatory effects of serotonin (100 microM). NO production in response to serotonin was investigated with 4,5-diaminofluorescein diacetate imaging. Although SNAP (100 microM) produced a rise in NO levels in all cells, only 22% of cells responded to serotonin with a moderate increase. The cGMP analog 8-bromo-cGMP (8-Br-cGMP; 0.2 and 2 mM) increased CBF, and the soluble guanylate cyclase inhibitor LY-83583 (10 microM) blocked the cilioexcitatory effects of SNAP and serotonin. These data suggest that NO has a constitutive cilioexcitatory effect in Helisoma embryos and that the stimulatory effects of serotonin and NO work through a cGMP pathway. It appears that in Helisoma cilia, NO activity is necessary, but not sufficient, to fully mediate the cilioexcitatory action of serotonin.

Novel functions of the matricellular proteins osteopontin and osteonectin/SPARC

Osteopontin (OPN) and osteonectin/SPARC (ON/SPARC) are prominent matricellular components of the extracellular matrix of mineralized tissues of bones and teeth in which they can regulate the formation and growth of hydroxyapatite crystals and influence a variety of cell activities. OPN regulates cell responses through several integrin receptors and is also a ligand for the CD44 receptor, through which it acts as a chemoattractant. Although a cell-surface receptor for SPARC has not been identified it can block cell-cell and cell-matrix interactions and inhibit cell migration and chemotaxis. OPN and SPARC also appear to function inside cells. Thus, OPN appears to exist in association with the CD44 receptor inside migratory cells, while intracellular SPARC is associated with axonemal tubulin in ciliated epithelial cells. Analyses of fibroblasts and peritoneal macrophages from OPN-null and CD44-null cells show impaired functionality involving migration and cell fusion required for osteoclast formation, while disruption of SPARC expression leads to developmental defects in Xenopus. To gain further insights into the intracellular functions of OPN and SPARC, we have used the yeast two-hybrid system to identify potential interacting molecules. Using full-length SPARC as bait the carboxy-terminal domain, which contains two EF-hand, high-affinity binding sites, was found to have transcriptional activity, while several novel proteins that interact with the amino-terminal domains of SPARC and full-length OPN have been identified. The identification of OPN and SPARC inside specialized cells introduces a novel concept in cellular regulation by matricellular proteins.

Distinct axonemal processes underlie spontaneous and stimulated airway ciliary activity

Cilia are small organelles protruding from the cell surface that beat synchronously, producing biological transport. Despite intense research for over a century, the mechanisms underlying ciliary beating are still not well understood. Even the nature of the cytosolic molecules required for spontaneous and stimulated beating is debatable. In an effort to resolve fundamental questions related to cilia beating, we developed a method that integrates the whole-cell mode of the patch-clamp technique with ciliary beat frequency measurements on a single cell. This method enables to control the composition of the intracellular solution while the cilia remain intact, thus providing a unique tool to simultaneously investigate the biochemical and physiological mechanism of ciliary beating. Thus far, we investigated whether the spontaneous and stimulated states of cilia beating are controlled by the same intracellular molecular mechanisms. It was found that: (a) MgATP was sufficient to support spontaneous beating. (b) Ca(2+) alone or Ca(2+)-calmodulin at concentrations as high as 1 microM could not alter ciliary beating. (c) In the absence of Ca(2+), cyclic nucleotides produced a moderate rise in ciliary beating while in the presence of Ca(2+) robust enhancement was observed. These results suggest that the axonemal machinery can function in at least two different modes.

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

beta(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 +/- 0.2 (SE) Hz (n = 80 measurements). R-albuterol (10 microM to 1 mM) stimulated CBF in a dose-dependent manner to maximally 24.4 +/- 5.4% above baseline. Racemic albuterol stimulated CBF to maximally 12.8 +/- 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 beta-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.

The mechanism of ciliary stimulation by acetylcholine: roles of calcium, PKA, and PKG

Stimulation of ciliary cells through muscarinic receptors leads to a strong biphasic enhancement of ciliary beat frequency (CBF). The main goal of this work is to delineate the chain of molecular events that lead to the enhancement of CBF induced by acetylcholine (ACh). Here we show that the Ca(2+), cGMP, and cAMP signaling pathways are intimately interconnected in the process of cholinergic ciliary stimulation. ACh induces profound time-dependent increase in cGMP and cAMP concentrations mediated by the calcium-calmodulin complex. The initial strong CBF enhancement in response to ACh is mainly governed by PKG and elevated calcium. The second phase of CBF enhancement induced by ACh, a stable moderately elevated CBF, is mainly regulated by PKA in a Ca(2+)-independent manner. Inhibition of either guanylate cyclase or of PKG partially attenuates the response to ACh of [Ca(2+)](i), but completely abolishes the response of CBF. Inhibition of PKA moderately attenuates and significantly shortens the responses to ACh of both [Ca(2+)](i) and CBF. In addition, PKA facilitates the elevation in [Ca(2+)](i) and cGMP levels induced by ACh, whereas an unimpeded PKG activity is essential for CBF enhancement mediated by either Ca(2+) or PKA.

Prolonged increase in ciliary beat frequency after short-term purinergic stimulation in human airway epithelial cells

Stimulation of ovine airway epithelial cells with 10 microM ATP for 1 min at 25 degrees C transiently increased both cytoplasmic calcium (fura-2 epifluorescence microscopy) and ciliary beat frequency (CBF; differential interference contrast microscopy) with a similar time course. Identical purinergic stimulation of human airway epithelial cells at 25 or 35 degrees C, however, lead to an increase in CBF that outlasted the calcium transient at least 20 min. While a nitric oxide synthase inhibitor had no effect, pre-treatment of human cells with inhibitors of cAMP-dependent kinase (PKA), 10 microM myristoylated PKA-inhibitory peptide and 1 microM KT-5720, as well as an inhibitor of adenylyl cyclase, 1 mM SQ22536, blocked the prolonged, but not calcium-coupled CBF increase. Addition of PKA inhibitors after purinergic stimulation only partially reduced CBF from its elevated plateau. Prolonged CBF increases did not depend on adenosine production as 10 microM UTP had an effect similar to ATP and 8-sulphophenyl-theophylline did not block them. After increasing human CBF in a PKA-dependent manner to a stable plateau with forskolin (10 microM), ATP caused only a transient, calcium-coupled CBF increase. Calcium transients were necessary for both short-term and prolonged CBF changes as ATP failed to produce CBF increases after emptying calcium stores with 1 microM thapsigargin. These data suggest that in human, but not ovine airway epithelial cells, ATP-induced calcium transients activate a signalling cascade including adenylyl cyclase and PKA. The resulting prolonged CBF stimulation does not rely only on PKA activity, suggesting that the decay of CBF is influenced by ciliary phosphatase activity.

SERCA activity is required for timely progression through G1/S

Changes in intracellular Ca2+ correlate with specific events in the cell cycle. Here we investigated the role of Ca2+ in the G1 phase. HEK 293 cells were arrested in mitosis and subjected to short-term treatments that alter Ca2+ homeostasis prior to their release into G1. Treatment with thapsigargin (TG), an irreversible inhibitor of the sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) lengthened the G1 phase. Moreover, TG treatment also resulted in a dramatic alteration in cellular morphology and attachment and in the reduction of MAPK activity and lower levels of cyclin D1 and cyclin E proteins. Treatments with reagents that transiently increase or decrease cytosolic Ca2+ or that temporarily inactivate SERCA did not alter any of the above parameters. Cells expressing a TG-resistant form of SERCA progressed normally through the G1/S transition after TG treatment. These results suggest that long-term SERCA inactivation affects cell cycle-dependent events and compromises progression through G1/S.

Differential neuronal localizations and dynamics of phosphorylated and unphosphorylated type 1 inositol 1,4,5-trisphosphate receptors

Type 1 inositol 1,4,5-trisphosphate receptors are phosphorylated by cyclic-AMP-dependent protein kinase A at serines 1589 and 1755, with serine 1755 phosphorylation greatly predominating in the brain. Inositol 1,4,5-trisphosphate receptor protein kinase A phosphorylation augments Ca(2+) release. To assess type 1 protein kinase A phosphorylation dynamics in the intact organism, we developed antibodies selective for either serine 1755 phosphorylated or unphosphorylated species. Immunohistochemical studies reveal marked variation in localization. For example, in the hippocampus the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is restricted to CA1, while the unphosphorylated receptor occurs ubiquitously in CA1-CA3 and dentate gyrus granule cells. Throughout the brain the phosphorylated type 1 inositol 1,4,5-trisphosphate receptor is selectively enriched in dendrites, while the unphosphorylated receptor predominates in cell bodies. Focal cerebral ischemia in rats and humans is associated with dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors, and glutamatergic excitation of cerebellar Purkinje cells mediated by ibogaine elicits dephosphorylation of type 1 inositol 1,4,5-trisphosphate receptors that precedes evidence of excitotoxic neuronal degeneration. We have demonstrated striking variations in regional and subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation that may influence normal physiological intracellular Ca(2+) signaling in rat and human brain. We have further shown that the subcellular distribution of inositol 1,4,5-trisphosphate receptor phosphorylation in neurons is regulated by excitatory neurotransmission, as well as excitotoxic insult and neuronal ischemia-reperfusion. Phosphorylation dynamics of type 1 inositol 1,4,5-trisphosphate receptors may modulate intracellular Ca(2+) release and influence the cellular response to neurotoxic insults.

Role of calcium and calmodulin in ciliary stimulation induced by acetylcholine

The goal of this work was to elucidate the molecular events underlying stimulation of ciliary beat frequency (CBF) induced by acetylcholine (ACh) in frog esophagus epithelium. ACh induces a profound increase in CBF and in intracellular Ca(2+) concentration ([Ca(2+)](i)) through M(1) and M(3) muscarinic receptors. The [Ca(2+)](i) slowly decays to the basal level, while CBF stabilizes at an elevated level. These results suggest that ACh triggers Ca(2+)-correlated and -uncorrelated modes of ciliary stimulation. ACh response is abolished by the phospholipase C (PLC) inhibitor U-73122 and by depletion of intracellular Ca(2+) stores but is unaffected by reduction of extracellular Ca(2+) concentration and by blockers of Ca(2+) influx. Therefore, ACh activates PLC and mobilizes Ca(2+) solely from intracellular stores. The calmodulin inhibitors W-7 and calmidazolium attenuate the ACh-induced increase in [Ca(2+)](i) but completely abolish the elevation in CBF. Therefore, elevation of [Ca(2+)](i) is necessary for CBF enhancement but does not lead directly to it. The combined effect of Ca(2+) elevation and of additional factors, presumably mobilized by Ca(2+)-calmodulin, results in a robust CBF enhancement.

Association of SPARC (osteonectin, BM-40) with extracellular and intracellular components of the ciliated surface ectoderm of Xenopus embryos

SPARC (Secreted Protein, Acidic, Rich in Cysteine) was detected by immunohistochemistry in the sensorial layer of the bilayered embryonic epidermis of Xenopus laevis during neurulation, when a subset of the sensorial cells are selected to differentiate into ciliated cell precursors. After the ciliated cells had intercalated into the outer layer and had undergone ciliogenesis, intense SPARC immunostaining was associated with the cilia and remained associated with the cilia throughout their persistence on the epidermis. Circumferential SPARC immunostaining was also detected at the interface between surface epithelial cells. Animal cap explants indicated that the embryonic activation of SPARC expression in the dorsal ectoderm does not require signaling from factors secreted by the underlying mesoderm. Immunoelectron microscopy revealed that SPARC is intimately associated with the 9 + 2 microtubule arrays of cilia. Our data indicate that SPARC plays a role in the development and function of the surface ciliated epidermis of Xenopus embryos. We propose that the counter-adhesive activity of SPARC facilitates the intercalation of ciliary cell precursors to the surface epithelial layer, where its Ca(2+)-binding abilities promote cell-cell adhesion. Based on its association with ciliary microtubule arrays, we also propose that intracellular SPARC may play a role in regulating ciliary beat frequency and polarity.

Differential expression and cellular distribution of centrin isoforms during human ciliated cell differentiation in vitro

Centrin protein is an ubiquitously expressed cytoskeletal component and is a member of the EF-hand superfamily of calcium-binding proteins. It was first discovered in the flagellar apparatus of unicellular green algae where it is involved in contraction of Ca(2+)-sensitive structures. Centrin protein is associated with centrosome-related structures such as spindle pole body in yeast, and centriole/basal bodies in flagellar and ciliated cells. Three centrin genes have been cloned in human cells. In this work, we have performed a comparative biochemical and functional analysis of centrin isoforms using a primary culture of human nasal epithelial cells which provides an efficient way to obtain a complete ciliated cell differentiation process. RT-PCR experiments show that the expression of the three human centrin genes increases during cell differentiation, and that only centrin 2 and 3 are expressed during cell proliferation. Using polyclonal antibodies raised against recombinant human centrin 2 and 3, we show a specific pattern of protein expression. Ultrastructural immunolocalization suggests that centrin proteins are involved in the early process of centriole assembly, as they are concentrated within the precursor structures of centriole/basal bodies. It also shows a differential localisation of centrin proteins in mature centriole/basal bodies, suggesting different functions for centrins 1/2 and centrin 3. This is also supported by functional analyses showing that centrin 1 and/or centrin 2 are involved in ciliary beating.

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

1. Average intracellular calcium concentration ([Ca2+]i) and ciliary beat frequency (CBF) were simultaneously measured in rabbit airway ciliated cells in order to elucidate the molecular events that lead to ciliary activation by purinergic stimulation. 2. Extracellular ATP and extracellular UTP caused a rapid increase in both [Ca2+]i and CBF. These effects were practically abolished by a phospholipase C inhibitor (U-73122) or by suramin. 3. The effects of extracellular ATP were not altered: when protein kinase C (PKC) was inhibited by either GF 109203X or chelerythrine chloride, or when protein kinase A (PKA) was inhibited by RP-adenosine 3', 5'-cyclic monophosphothioate triethylamine (Rp-cAMPS). 4. Activation of PKC by phorbol 12-myristate, 13-acetate (TPA) had little effect on CBF or on [Ca2+]i, while activation of PKA by forskolin or by dibutyryl-cAMP led to a small rise in CBF without affecting [Ca2+]i. 5. Direct activation of protein kinase G (PKG) with dibutyryl-cGMP had a negligible effect on CBF when [Ca2+]i was at basal level. However, dibutyryl-cGMP strongly elevated CBF when [Ca2+]i was elevated either by extracellular ATP or by ionomycin. 6. The findings suggest that the initial rise in [Ca2+]i induced by extracellular ATP activates the NO pathway, thus leading to PKG activation. In the continuous presence of elevated [Ca2+]i the stimulated PKG then induces a robust enhancement in CBF. In parallel, activated PKG plays a central role in Ca2+ influx via a still unidentified mechanism, and thus, through positive feedback, maintains CBF close to its maximal level in the continuous presence of ATP.