Effects of TCPP and TCEP exposure on human corneal epithelial cells: Oxidative damage, cell cycle arrest, and pyroptosis.

Tris(2-chloroisopropyl) phosphate (TCPP) and Tris(2-chloroethyl) phosphate (TCEP) are the widely used organophosphorus flame retardants indoors and easily accessible to the eyes as the common adhesive components of dust and particle matter, however, hardly any evidence has demonstrated their corneal toxicity. In this study, the adverse effects of TCPP, TCEP, and TCPP + TCEP exposure on human corneal epithelial cells (HCECs) were investigated. The cell viability and morphology, intracellular reactive oxygen species (ROS), cell cycle, and the expressions of cell cycle and pyroptosis-related genes were assessed to explain the underlying mechanisms. Compared to individual exposure, co-exposure to TCPP20+TCEP20 showed higher cytotoxicity with a sharp decrease of >30% in viability and more serious oxidative damage by increasing ROS production to 110.92% compared to the control group. Furthermore, the cell cycle arrested at the S phase (36.20%) was observed after combined treatment, evidenced by the upregulation of cyclin D1, CDK2, CDK4, CDK6, p21, and p27. Interestingly, pyroptosis-related genes GSDMD, Caspase-1, NLRP3, IL-1ß, IL-18, NLRP1, and NLRC4 expressions were promoted with cell swelling and glowing morphology. Oxidative stress and cell cycle arrest probably acted as a key role in TCPP20+TCEP20-induced cytotoxicity and pyroptosis in HCECs. Our results suggested that TCPP20+TCEP20 co-exposure induced severer corneal damage, further illustrating its significance in estimating indoor health hazards to humans.

Indoor air pollution and human ocular diseases: Associated contaminants and underlying pathological mechanisms.

People spend a long time indoors, especially young children. The risk of indoor pollution on human health is one of the current hotspots in environmental and public health. The human ocular surface is highly susceptible to indoor environment quality. Epidemiological data have linked human ophthalmological disorders with exposure to indoor pollution. In this review, we summarized the adverse impacts of indoor pollution on the human ocular surface. Several studies demonstrated that indoor contaminants including particulate matter, volatile/semi-volatile organic compounds, heavy metals, and fuel combustion and cigarette smoke exposure were associated with the incidence of human dry eye, conjunctivitis, glaucoma, cataracts, age-related macular degeneration, and keratitis. In addition, toxicological investigations revealed that indoor pollution-induced induced chronic inflammation, oxidative damage, and disruption of tight junctions are the main underlying pathological mechanisms for ocular surface diseases. Taken together, this review may expand the understanding of pollution-induced eye disorder and highlight the importance of reducing associated contaminants to decrease their detrimental effects on human eyes.

Organophosphorus Flame Retardant TCPP Induces Cellular Senescence in Normal Human Skin Keratinocytes: Implication for Skin Aging.

Tris (1-chloro-2-propyl) phosphate (TCPP) is one of the most frequently detected organophosphorus flames in the environment. Continuous daily exposure to TCPP may harm human skin. However, little is known about the adverse effects of TCPP on human skin. In this study, we first evaluated the detrimental effects and tried to uncover the underlying mechanisms of TCPP on human skin keratinocytes (HaCaT) after 24 h exposure. We found that TCPP caused a concentration-dependent decrease in HaCaT cell viability after exposure to 1.56-400 µg/mL for 24 h, with an IC50 of 275 µg/mL. TCPP also promoted the generation of intracellular reactive oxygen species (ROS) and triggered DNA damage, evidenced by an increase of phosphorylated histone H2A.X (γH2A.X) in the nucleus. Furthermore, the cell cycle was arrested at the G1 phase at 100 µg/mL by upregulation of the mRNA expression of p53 and p21 and downregulation of cyclin D1 and CDK4 expression. Additionally, both the senescence-associated-ß-galactosidase activity and related proinflammatory cytokine IL-1ß and IL-6 were elevated, indicating that TCPP exposure caused cellular senescence may be through the p53-dependent DNA damage signal pathway in HaCaT cells. Taken together, our data suggest that flame-retardant exposure may be a key precipitating factor for human skin aging.

Mechanical behavior and reinforcement mechanism of nanoparticle cluster fillers in dental resin composites: Simulation and experimental study.

OBJECTIVES: In dental resin composites (DRCs), the structure of fillers has a great impact on the mechanical behavior. The purpose of this study is to gain an in-depth understanding of the reinforcement mechanism and mechanical behavior of DRCs with nanoparticle clusters (NCs) fillers, thereby providing a guidance for the optimal design of filler structures for DRCs. METHODS: This work pioneers the use of discrete element method (DEM) simulations combined with experiments to study the mechanical behavior and reinforcement mechanism of DRCs with NCs fillers. RESULTS: The uniaxial compressive strength (UCS) of NCs-reinforced DRCs have an improvement of 9.58 % and 15.02 % in comparison with nanoparticles (NPs) and microparticles (MPs), respectively, because of the ability of NCs to deflect cracks and absorb stress through gradual fracturing. By using NCs and NPs as co-fillers, the internal defects of DRCs can be reduced, resulting in a further improvement of UCS of DRCs by 6.21 %. Furthermore, the mechanical properties of DRCs can be effectively improved by increasing the strength of NCs or reducing the size of NCs. SIGNIFICANCE: This study deepens the understanding of relationship between filler structure and mechanical behavior in DRCs at the mesoscale and provides an avenue for the application of DEM simulations in composite materials.

Effects of Nickel at Environmentally Relevant Concentrations on Human Corneal Epithelial Cells: Oxidative Damage and Cellular Apoptosis.

Nickel (Ni) is ubiquitous in the environment and evidence has suggested that Ni can cause ocular surface inflammation, especially in fine particulate matter and personal products. Continuous daily exposure to Ni-containing dust may adversely impact the human cornea, whereas the underlying mechanism of this phenomenon remains not fully understood. Here, human corneal epithelial cells (HCEC) were employed to analyze the toxicity of Ni via detections of cell morphology, cell viability, reactive oxygen species production, cell apoptosis rate, and apoptotic gene expression levels after exposure for 24 h to uncover the damage of Ni to the cornea. A concentration-dependent inhibition of HCECs' viability and growth was observed. In particular, Ni at 100 µM significantly decreased cell viability to 76%, and many cells displayed an abnormal shape and even induced oxidative damage of HCEC by increasing ROS to 1.2 times, and further led to higher apoptosis (24%), evidenced by up-regulation of apoptotic genes Caspase-8, Caspase-9, NF-κB, IL-1ß, and Caspase-3, posing a risk of dry eye. Our study suggested that Ni induces apoptosis of HCEC through oxidative damage. Therefore, Ni pollution should be comprehensively considered in health risks or toxic effects on the ocular surface.

Spray-drying-assisted fabrication of CaF2/SiO2 nanoclusters for dental restorative composites.

OBJECTIVE: The objective of this study is to develop novel CaF2/SiO2 nanoclusters (NCs) fillers, which can endow the dental resin composites (DRCs) with excellent mechanical properties, stable and sustained fluoride ion release, and good antibacterial activity. METHODS: The CaF2/SiO2 NCs were efficiently fabricated by assembling CaF2/SiO2 nanoparticles (NPs) as building blocks with a spray-drying technology. CaF2/SiO2 NCs with different SiO2 coating amounts (20 wt%, 50 wt% and 80 wt%) were incorporated into the DRCs at the filler content of 55 wt% for the measurement of mechanical properties including flexural strength, flexural modulus, compressive strength, and hardness. The effect of the filling amount of CaF2/50SiO2 NCs (50 represents 50 wt% SiO2 coating amount) in the DRCs was investigated, while CaF2/50SiO2 NPs were adopted as comparison group. The fluoride ion release and antibacterial activity of the DRCs with the optimal mechanical performances were evaluated. Furthermore, the statistical analyses were performed for mechanical properties. RESULTS: Spherical CaF2/50SiO2 NCs with an average size of 2.4 µm were obtained at the feed rate of 7.4 mL/min and the CaF2/50SiO2 NPs solid content of 2 wt% in the suspension. The optimum comprehensive performances of the DRCs can be achieved by filling 55 wt% CaF2/50SiO2 NCs. Compared with CaF2/50SiO2 NPs, the filling amount of CaF2/50SiO2 NCs was increased by 5 wt% (50-55 wt%), and under the same filling amount of 50 wt%, the flexural strength, flexural modulus, compressive strength, and hardness of the DRCs containing CaF2/50SiO2 NCs were improved by 9.8%, 17.7%, 7.5% and 69.8%, respectively. Furthermore, the DRCs filled with 50 wt% CaF2/50SiO2 NCs exhibited more cumulative F-release by 126% and more stable F-release rate than the counterpart filled with 50 wt% CaF2/50SiO2 NPs after immersed for 1800 h. And 55 wt% CaF2/50SiO2 NCs filled DRCs could inhibit the growth of S. mutans, reaching an antibacterial ratio of 93%. SIGNIFICANCE: The spray-dried CaF2/50SiO2 NCs are promising fillers for the development of high-performance multifunctional DRCs.

Dermal bioaccessibility and cytotoxicity of heavy metals in urban soils from a typical plateau city: Implication for human health.

The dermal exposure of heavy metals in contaminated urban soils poses huge environmental health risks globally. However, their dermal bioaccessibility and adverse effects on human skin cells were not fully understood. In this study, we measured the total and dermal bioaccessibility of Cr, As, Cd, Pb, and Cu in four selected urban soil samples from Kunming, Yunnan, China, and evaluated the cellular responses of these bioaccessible extracts on human keratinocytes (HaCaT). Among all the metals, only As in Soil-3 (S3) exceeded Chinese risk screening and Yunnan background values at 38.2 mg/kg. The average concentrations of Cr, As, Cd, Pb, and Cu in all soil samples were 47.79, 15.50, 3.11, 104.27, and 180.29 mg/kg respectively. Although relatively high concentrations of heavy metals were detected in soil samples, the highest dermal bioaccessibility of Cd was 3.57% with others' being lower than 1%. The bioaccessible dermal-absorbed doses (DADs) of Cr, As, Cd, Pb, and Cu from soils reflected acceptable health risks since all DADs were below the corresponding derived dermal reference values. However, the toxic data showed the extracts of S3 and S4 presented certain cytotoxicity in HaCaT cells, indicating the existing models based on dermal bioaccessibility and DADs may be not accurate enough to assess their human health risk. Taken together, the human health risk assessment should be modified by taking their skin cytotoxicity into account.

Efficient prediction of the packing density of inorganic fillers in dental resin composites for excellent properties.

OBJECTIVE: The purpose of this study is to develop a mathematical model for efficient prediction of the packing density of different filler formulations in dental resin composites (DRCs), and to study properties of DRCs at the maximum filler loading (MFL), thereby providing an effective guidance for the design of filler formulations in DRCs to obtain excellent properties. METHODS: The packing density data generated by discrete element model (DEM) simulation were used to re-derive the parameters of 3-parameter model. The modifier effect was also induced to modify the 3-parameter model. DRCs with 10 filler formulations were selected to test properties at the MFL. The packing densities of binary and ternary mixes in DRCs were calculated by 3-parameter model to explore the regularity of composite packing. RESULTS: The predicted packing density was validated by simulation and experimental results, and the prediction error is within 1.40 vol%. The optimization of filler compositions to obtain a higher packing density is beneficial to enhancing the mechanical properties and reducing the polymerization shrinkage of DRCs. In binary mixes, the maximum packing density occurs when the volume fraction of small fillers is 0.35-0.45, and becomes higher with the reduction of particle size ratio. In ternary mixes, the packing density can reach the maximum value when the volume fractions of large and small fillers are in the 0.5-0.75 and 0.15-0.4 ranges, respectively. SIGNIFICANCE: The modified 3-parameter model can provide an effective method to design the multi-level filler formulations of DRCs, thereby improving the performance of the materials.

Antibacterial activity and reinforcing effect of SiO2-ZnO complex cluster fillers for dental resin composites.

The accumulation of bacteria at the margin of dental resin composites is the main reason for secondary caries, which may further cause failure of prosthodontics. Therefore, antibacterial activity is highly required. However, the addition of antibacterial agents or fillers weakens the mechanical or aesthetic properties of composites. In this work, regular-shaped SiO2-ZnO complex clusters (CCs) constructed by spray-drying technology can enhance the antibacterial activity while maintaining the mechanical and aesthetic properties of dental resin composites. The results show that the regular shape and closely packed structure of nanoparticle clusters were not corrupted by the introduction of ZnO particles. As compared to resin composites filled with SiO2 nanoparticle clusters, the comprehensive performances of composites containing SiO2-ZnO CCs were further improved, and the composites filled with 70 wt% Si66Zn4 (CCs composed of 66/70 SiO2 and 4/70 of ZnO) exhibited superior antibacterial capability (antibacterial ratio >99.9%) and acceptable depth of cure, degree of conversion, and biocompatibility. The cooperation of different fillers is highly essential for resin composites to achieve enhanced multifunctional performance.

A new method for predicting the maximum filler loading of dental resin composites based on DEM simulations and experiments.

OBJECTIVE: The inorganic fillers in dental resin composites can enhance their mechanical properties and reduce polymerization shrinkage. When the usage amount of inorganic fillers is closed to maximum filler loading (MFL), the composites will usually achieve optimal performances. This study aims to develop a method that can predict the MFL of dental resin composites for the optimization of filler formulations. METHODS: A method based on discrete element method (DEM) simulations and experiments was firstly developed to predict the MFL of spherical silica particles for single-level and multi-level filling. RESULTS: The results indicate that the presence of modifier can increase the MFL, and the MFL increment can be exponentially changed with the content of the modifier. Compared with the single-level filling, the addition of secondary fillers is beneficial to increase the MFL, and the increment can be affected by the particle size and size ratio. The prediction results show a good agreement with the experiment results. SIGNIFICANCE: The accuracy of prediction results indicates a great potential of DEM simulations as a numerical experimental method in studying the MFL, and provides an effective method for the optimization of filler formulations.

[Effect of phosphodiesterase inhibitor on expression of IL-8 mRNA in peripheral blood mononuclear cells from COPD patients].

AIM: To explore the inhibitory mechanism of phosphodiesterase(PDE) inhibitor on expression of IL-8 mRNA in peripheral blood mononuclear cells (PBMCs) from chronic obstructive pulmonary disease(COPD) patients. METHODS: PBMCs isolated from 20 COPD patients and 15 healthy subjects were co-cultured with non-selective inhibitor theophylline or PDE type IV inhibitor Rolipram. The expression of IL-8 mRNA was assayed by RT-PCR. The expression of NF-kappaB was determined by immunocytochemical staining. The content of I-kappaB protein was detected by Western blot. RESULTS: The expression of IL-8 mRNA was elevated and the percentage of NF-kappaB nucleus positive cells was higher in COPD patients than in normal controls(P<0.01), while the expression of I-kappaB was lower in COPD patients (P<0.01). Theophylline of 1 mmol/L caused a decrease in the percentage of NF-kappaB nucleus positive cells (P<0.05). The expression of IL-8 mRNA and I-kappaB were not affected by theophylline at the dose of 100 micromol/L or 1 mmol/L. Rolipram inhibited the expression of IL-8 mRNA and the activation of NF-kappaB(P<0.05). CONCLUSION: The results indicated that IL-8 mRNA may play a pathogenic role in the development of COPD and that selective PDE type IV inhibitor Rolipram inhibit the expression of IL-8 mRNA via NF-kappaB.

[The isolation and expansion of gamma delta T cells in peripheral blood and bronchoalveolar lavage fluid].

AIM: To explore the method of selective culture of gamma delta T cells in peripheral blood and bronchoalveolar lavage fluid(BALF) for obtaining pure gamma delta T cell subset. METHODS: A novel attack-panning method for selectively culturing gamma delta T cells was set up. The peripheral blood mononuclear cells (PBMCs) and BALF were isolated by Ficoll-hypaque density gradient centrifugation (n=10). alpha beta T cells in PBMCs were depleted by complement-dependent-cytotoxicity(CDC) after the monocytes/macrophages were removed by adherence. The gamma delta T cells in PBMCs were cultivated selectively using anti-TCR gamma delta monoclonal antibody and IL-2. The proliferation of gamma delta T cells were observed by plotting growth curve. The purity of gamma delta T cells were detected by flow cytometry and immunohistochemistry. RESULTS: Stimulated by anti-TCR gamma delta mAb and IL-2, gamma delta T cells of peripheral blood and BALF could proliferate for a few days. The purity of gamma delta T cells obtained by Attack-panning method was 81%-99%. CONCLUSION: The attack-panning method can get pure gamma delta T cells from peripheral blood and BALF.

[A study of helper T cell (Th)1/Th2 immune response pattern of gammadeltaT cells in asthma].

OBJECTIVE: To explore the mode of immune responses of gammadeltaT cells in asthma and the role of gammadeltaT cell subsets in the pathogenesis of asthma. METHODS: Wistar rats were sensitized and challenged with ovalbumin to establish an asthmatic model (n = 10, for each group). "Attack-panning" method was used to culture selective gammadeltaT cells. The percentage of gammadelta T cells among cultured cells was determined by flow cytometry. The levels of interleukin (IL)-4 and interferon-gamma (IFN-gamma) were measured by ELISA. The expression of IL-4 mRNA and IFN-gamma mRNA was determined by in situ hybridization. RESULTS: In the asthmatic group, IL-4 and IFN-gamma were detectable at the same time in cultured supernatant of gammadeltaT cells in peripheral blood mononuclear cells (PBMC) or broncho-alveolar fluid (BALF), and the level of IL-4 [PBMC: (40.5 +/- 3.7) ng/L, BALF: (49.6 +/- 3.1) ng/L] increased as compared with the control group [PBMC: (26.1 +/- 2.1) ng/L, BALF: (23.6 +/- 1.7) ng/L; all P < 0.01], while the level of IFN-gamma [PBMC: (17.6 +/- 2.5) ng/L, BALF: (28.5 +/- 3.6) ng/L] decreased as compared with the control group [PBMC: (24.3 +/- 1.7) ng/L, BALF: (38.4 +/- 2.8) ng/L; all P < 0.01]. In the asthmatic group, the percentage of IL-4 mRNA positive-staining cells [PBMC: (76.2 +/- 7.2)%, BALF: (85.7 +/- 8.4)%] among the gammadeltaT cells significantly increased as compared with the control group [PBMC: (20.6 +/- 5.3)%, BALF: (25.0 +/- 6.8)%; all P < 0.01], while the percentage of IFN-gammamRNA positive-staining cells [PBMC: (30.9 +/- 6.7)%, BALF: (41.5 +/- 3.6)%] among the gammadeltaT cells significantly decrease as compared with the control group [PBMC: (60.1 +/- 4.2)%, BALF: (53.8 +/- 5.1)%; all P < 0.01]. CONCLUSIONS: gammadeltaT cells can secrete both IL-4 and IFN-gamma at the same time, or there are two subsets of gammadeltaT cells which can secrete either IL-4 or IFN-gamma in PBMC or BALF in asthma. Th1/Th2 immune response mode is present in gammadeltaT cells of asthma and Th2-cytokine profile predominates. gammadeltaT cells is involved in the pathogenesis of asthma.

[The role of delayed rectifier potassium channels in the regulation of bronchial smooth muscle tension in asthmatic rats].

OBJECTIVE: To investigate the role of delayed rectifier potassium channels (K(V)) in the regulation of bronchial smooth muscle tension in asthmatic rats and their effects on bronchial reactivity in vitro. METHODS: By using a specific potassium channel blocker, the bronchial contraction induced by spasmogens was observed in normal and asthmatic rats with the isometric tension recording technique. RESULTS: (1) K(V) blocker 4-aminopyridine (4-AP) caused concentration-dependent bronchial contraction in vitro. The concentration-response curve to 4-AP in the asthmatic group showed a left displacement with bigger pD(2) (the negative logarithm of the drug concentration causing 50% of maximal effect, 2.58 +/- 0.07, n = 10, P < 0.001) and no change in E(max) [maximal effect, (32 +/- 5) mg/mg, P > 0.05], compared with pD(2) (2.12 +/- 0.04, n = 10) and E(max) [(31 +/- 6) mg/mg] obtained in the control group; (2) In the control group, pre-treatment with 0.1 mmol/L 4-AP displaced the concentration-response curves to ET-1 and histamine to the left. pD(2) (for ET-1 and histamine) before and after 4-AP treatment was 6.27 +/- 0.38, 5.59 +/- 0.27 and 6.80 +/- 0.47, 6.42 +/- 0.14 respectively (P < 0.01). E(max) before and after 4-AP treatment was (36 +/- 8) mg/mg, (36 +/- 8) mg/mg and (40 +/- 8) mg/mg, (39 +/- 9) mg/mg respectively (P > 0.05); (3) In the asthmatic group, pre-treatment with 0.1 mmol/L 4-AP had no effect on the concentration-response curve to ET-1 and histamine. There was no significant difference (P > 0.05) in pD(2) before (6.51 +/- 0.07, 5.86 +/- 0.14 respectively) and after (6.48 +/- 0.16, 5.96 +/- 0.08 respectively) 4-AP treatment, and in E(max) before [(61 +/- 8) mg/mg, (54 +/- 11) mg/mg respectively] and after [(65 +/- 10) mg/mg, (55 +/- 9) mg/mg respectively] 4-AP treatment. CONCLUSION: The activity of K(V) decreases in bronchial smooth muscle isolated from asthmatic rats compared with that obtained from normal ones. This change may be involved in the bronchial hyperreactivity to some spasmogens in vitro in asthmatic rats.

Isoprenaline and aminophylline relax bronchial smooth muscle by cAMP-induced stimulation of large-conductance Ca2+-activated K+ channels.

AIM: To investigate whether the relaxation of bronchial smooth muscle induced by isoprenaline and aminophylline is mediated by large conductance Ca2+-activated K+ channels (BK(Ca)) via cAMP-dependent mechanism. METHODS: With isometric tension recording, the role of BK(Ca) in relaxations of rat bronchial strips induced by isoprenaline and aminophylline was determined. With perforated patch-clamp technique, BK(Ca) currents were observed in freshly isolated rat bronchial myocytes. RESULTS: Tetraethylammonium 5 mmol/L, a BK(Ca) blocker, caused a significant rightward shift in the concentration-response curves of isoprenaline and aminophylline (about 4.26-fold and 3.78-fold, respectively) in methacholine-precontracted rat bronchial strips. Isoprenaline 1 micromol/L caused a significant increase in BK(Ca) current from (94+/-15) pA/pF to (186+/-30) pA/pF (voltage steps from -60 mV to +50 mV, n=10, P<0.01), which was partly abolished by Rp-cAMP 100 micromol/L, a protein kinase A inhibitor. Furthermore, current-voltage relationship(I-V) curve exhibited an upward shift, and the peak current density was significantly raised (n=10, P<0.01) by ramp depolarization from -100 mV to +100 mV. Aminophylline 1 mmol/L caused a significant increase in BK(Ca) current from (90+/-10) pA/pF to (166+/-25) pA/pF (voltage steps from -60 mV to +50 mV, n=11, P<0.01), which was partly abolished by Rp-cAMP 100 micromol/L. Furthermore, the I-V curve exhibited an upward shift, and the peak current density was significantly raised (n=11, P<0.01) by ramp depolarization from -100 mV to +100 mV. CONCLUSION: The relaxations induced by isoprenaline and aminophylline were, at least partly, mediated by cAMP-stimulation of BK(Ca) in rat bronchial smooth muscle.

[Effect of nitric oxide on NF-kappaB activation induced by cigarette smoke extract in rat alveolar macrophage].

AIM: To explore the effect of nitric oxide on NF-kappaB activation in rat alveolar macrophage(AM) induced by cigarette smoke extract(CSE) and the involved mechanism. METHODS: AMs were co-cultured with NO precursor L-arginine (L-Arg) or inhibitor of inducible nitric oxide synthase L-N(6)(1-iminoethyl)lysine (L-NIL) and CSE. The expression of NF-kappaB was determined by immunocytochemistrical staining, the content of I-kappaB protein was detected by Western blot, the level of NO in supernatant was assayed by Griess reaction. RESULTS: CSE could induce NF-kappaB activation and decrease level of I-kappaB. L-Arg augmented CSE-induced NF-kappaB activation and decreased I-kappaB content at low concentration while inhibited CSE-induced NF-kappaB activation at high concentration, but there was not any significant difference of the expression of I-kappaB. The percentage of NF-kappaB nucleus dyeing positive cells was lower and the expression of I-kappaB was higher in response to CSE plus various concentrations of L-NIL as compared with that in response to CSE alone (P<0.01). The changes induced by L-NIL were concentration-dependent. CONCLUSION: NO may up-regulate and down-regulate the activation of NF-kappaB induced by CSE according to difference in NO concentration in AMs.

[Investigation of regulating effects of potassium channels on the tone of rat bronchial smooth muscle].

AIM: To investigate the role of three K+ channels-delayed rectifier K+ channel (Kv), large-conductance Ca(2+)-activated K+ channel (BK(Ca)) and ATP-sensitive K+ channel (K(ATP)) in the regulation of the resting and contracting tone of rat bronchial smooth muscle (BSM). METHODS: By measuring the isometric tone of bronchial strips in vitro, the regulating effects of the three K+ channels on the tone of rat BSM were observed. RESULTS: (1) Kv blocker 4-aminopyridine (4-AP) caused concentration dependent contraction in resting bronchial strips, but BK(Ca) blocker tetraethylammonium (TEA) and K(ATP) blocker glibenclamide (Glib) had no such effects. (2) The bronchial epithelium had no effects on the contraction induced by 4-AP, but nifedipine, a Ca2+ channel blocker, significantly suppressed it. (3) Before or after treatment with 0.1 mmol/L histamine or 50 mmol/L KCl, administration of TEA (1 or 5 mmol/L) or 0.1 mmol/L 4-AP could significantly increase the contraction induced by histamine and KCl in bronchial strips. But Glib (10 micromol/L) had no effect on it. CONCLUSION: Not BK(Ca) and K(ATP) but Kv participated in the regulation of the resting tone in rat BSM. The closure of BK(Ca) or Kv increased the contracting tone induced by histamine or KCl in rat BSM in vitro, but K(ATP) had no such effect on it.