Functional expression of the TMEM16 family of calcium-activated chloride channels in airway smooth muscle

Airway smooth muscle hyperresponsiveness is a key component in the pathophysiology of asthma. Although calcium-activated chloride channel (CaCC) flux has been described in many cell types, including human airway smooth muscle (HASM), the true molecular identity of the channels responsible for this chloride conductance remains controversial. Recently, a new family of proteins thought to represent the true CaCCs was identified as the TMEM16 family. This led us to question whether members of this family are functionally expressed in native and cultured HASM. We further questioned whether expression of these channels contributes to the contractile function of HASM. We identified the mRNA expression of eight members of the TMEM16 family in HASM cells and show immunohistochemical evidence of TMEM16A in both cultured and native HASM. Functionally, we demonstrate that the classic chloride channel inhibitor, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), inhibited halide flux in cultured HASM cells. Moreover, HASM cells displayed classical electrophysiological properties of CaCCs during whole cell electrophysiological recordings, which were blocked by using an antibody selective for TMEM16A. Furthermore, two distinct TMEM16A antagonists (tannic acid and benzbromarone) impaired a substance P-induced contraction in isolated guinea pig tracheal rings. These findings demonstrate that multiple members of this recently described family of CaCCs are expressed in HASM cells, they display classic electrophysiological properties of CaCCs, and they modulate contractile tone in airway smooth muscle. The TMEM16 family may provide a novel therapeutic target for limiting airway constriction in asthma.

A simple method of mouse lung intubation

A simple procedure to intubate mice for pulmonary function measurements would have several advantages in longitudinal studies with limited numbers or expensive animal. One of the reasons that this is not done more routinely is that it is relatively difficult, despite there being several published studies that describe ways to achieve it. In this paper we demonstrate a procedure that eliminates one of the major hurdles associated with this intubation, that of visualizing the trachea during the entire time of intubation. The approach uses a 0.5 mm fiberoptic light source that serves as an introducer to direct the intubation cannula into the mouse trachea. We show that it is possible to use this procedure to measure lung mechanics in individual mice over a time course of at least several weeks. The technique can be set up with relatively little expense and expertise, and it can be routinely accomplished with relatively little training. This should make it possible for any laboratory to routinely carry out this intubation, thereby allowing longitudinal studies in individual mice, thereby minimizing the number of mice needed and increasing the statistical power by using each mouse as its own control.

Variation in airway responsiveness of male C57BL/6 mice from 5 vendors

Mice are now the most commonly used animal model for the study of asthma. The mouse asthma model has many characteristics of the human pathology, including allergic sensitization and airway hyperresponsiveness. Inbred strains are commonly used to avoid variations due to genetic background, but variations due to rearing environment are not as well recognized. After a change in mouse vendors and a switch from C57BL/6J mice to C57BL/6N mice, we noted significant differences in airway responsiveness between the substrains. To further investigate the effect of vendor, we tested C57BL/6N mice from 3 other vendors and found significant differences between several of the substrains. To test whether this difference was due to genetic drift or rearing environment, we purchased new groups of mice from all 5 vendors, bred them in separate vendor-specific groups under uniform environmental conditions, and tested male first generation (F1) offspring at 8 to 10 wk of age. These F1 mice showed no significant differences in airway responsiveness, indicating that the rearing environment rather than genetic differences was responsible for the initial variation in pulmonary phenotype. The environmental factors that caused the phenotypic variation are unknown. However, differences between vendor in feed components, bedding type, or microbiome could have contributed. Whatever the basis, investigators using mouse models of asthma should be cautious in comparing data from mice obtained from different vendors.

Animal models of airway inflammation and airway smooth muscle remodelling in asthma

Asthma is a complex disease that involves chronic inflammation and subsequent decline in airway function. The widespread use of animal models has greatly contributed to our understanding of the cellular and molecular pathways underlying human allergic asthma. Animal models of allergic asthma include smaller animal models which offer 'ease of use' and availability of reagents, and larger animal models that may be used to address aspects of allergic airways disease not possible in humans or smaller animal models. This review examines the application and suitability of various animal models for studying mechanisms of airway inflammation and tissue remodelling in allergic asthma, with a specific focus on airway smooth muscle.

An improved simple method of mouse lung intubation

Given the ubiquitous use of mice to study lung disease, it is curious that more investigators do not use repeated intubation to study mechanical and cellular changes in individual mice. One of the reasons for this limited use of intubation is that it is relatively difficult, despite there being several published studies that describe ways to achieve it. In this paper, we describe a complete procedure, including novel approaches that simplify this intubation, so that it can be routinely accomplished with relatively little training. The technique can also be set up with relatively little expense and expertise. This should make it possible for any laboratory to routinely carry out this intubation, thereby allowing longitudinal studies in individual mice and potentially increasing the statistical power by using each mouse as its own control.

Sex differences in mouse models of asthma

Differences in disease susceptibility and prognosis between men and women are known to occur in the incidence and development of neurodegenerative, cardiovascular, and immunological disorders. In the lung there are also sex-based differences in the incidence, prevalence, and pathogenesis of lung cancer, cystic fibrosis, COPD, and asthma. In the general population, sex-based differences in asthma have been shown by epidemiologic studies, but unfortunately these studies are not consistent in their conclusions. This variability in human epidemiological studies justifies the need for more focused studies of the effects of specific hormones. Such specific mechanistic studies can most easily be performed in animal models, and since mouse models have the potential for separating specific genetic factors from environmental and exogenous factors, this species has become increasingly important in the design, analysis, and interpretation of asthma research. This review will document the male and female differences in airway function of naïve and sensitized mouse models, as well as the great variability in the functional measurements of airway tone. Until the situation is better understood, this variability between males and females should be kept in mind when designing, analyzing, and interpreting studies of smooth muscle responses in animal models and human subjects.

The effects of systemic lidocaine on airway tone and pulmonary function in asthmatic subjects

BACKGROUND

To prevent reflex-induced bronchoconstriction in patients with asthma, local anesthetics are commonly administered by aerosol or IV as adjunct medication. Lidocaine attenuates responsiveness to a neurally active stimulus that increases tone, but there is scant information about the effect of lidocaine on baseline airway tone. Therefore we examined the effects of IV lidocaine on baseline airway tone in asthmatic subjects.

METHODS

Small, medium, and large airways (2-5, 5-8, >8 mm diameter) were analyzed by computed tomography in 15 asthmatic volunteers under baseline conditions and during infusion of lidocaine. Changes in luminal airway diameter and wall thickness from baseline to during lidocaine infusion, and the change in pulmonary function induced by lidocaine, were analyzed.

RESULTS

Lidocaine caused a significant decrease in the forced expiratory volume in 1 s pulmonary function measure (7 +/- 2%, P = 0.006). There was also a small but significant decrease in the airway luminal diameter at total lung capacity during lidocaine infusion compared to baseline (-3 +/- 0.5%, P < 0.001). Moreover, there was a significant correlation between the change in forced expiratory volume in 1 s and the change in airway luminal diameter at total lung capacity (r2 = 0.47, P = 0.01).

CONCLUSION

Lidocaine, which reduces airway responsiveness to drugs that cause bronchospasm through sensory nerve activation, did not reduce baseline airway tone. Instead, even when administered IV, lidocaine significantly increased airway tone and caused airway narrowing. Therefore, while the administration of lidocaine can prevent intubation-induced bronchospasm, the airways should be constantly monitored by auscultation even during IV lidocaine administration.