Abnormal tracheal smooth muscle function in the CF mouse.

Increased airway smooth muscle (ASM) contractility is thought to underlie symptoms of airway hyperresponsiveness (AHR). In the cystic fibrosis (CF) airway, ASM anomalies have been reported, but have not been fully characterized and the underlying mechanisms are largely unknown. We examined ASM in an adult CF mouse tracheal ring preparation, and determined whether changes in contractility were associated with altered ASM morphology. We looked for inherent changes in the cellular pathways involved in contractility, and characterized trachea morphology in the adult trachea and in an embryonic lung culture model during development. Results showed that that there was a reduction in tracheal caliber in CF mice as indicated by a reduction in the number of cartilage rings; proximal cross-sectional areas of cftr (-/-) tracheas and luminal areas were significantly smaller, but there was no difference in the area or distribution of smooth muscle. Morphological differences observed in adult trachea were not evident in the embryonic lung at 11.5 days gestation or after 72 h in culture. Functional data showed a significant reduction in the amplitude and duration of contraction in response to carbachol (CCh) in Ca-free conditions. The reduction in contraction was agonist specific, and occurred throughout the length of the trachea. These data show that there is a loss in the contractile capacity of the CF mouse trachea due to downregulation of the pathway specific to acetylcholine (ACh) activation. This reduction in contraction is not associated with changes in the area or distribution of ASM.

Embryonic lung growth is normal in a cftr-knockout mouse model.

The role of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel in embryonic lung growth remains uncertain. The authors used an established embryonic lung culture model to investigate the impact of cftr knockout on lung growth, airway peristalsis, and airway smooth muscle (ASM) distribution. Lung area, perimeter, lung bud count, and frequency of contraction were similar in wild-type (cftr +/+) and cftr knockout mice (cftr -/-). The percentage of mitotic cells was also consistent between genotypes in mesenchyme and epithelium. Smooth muscle distribution surrounding the airway appeared normally distributed in all genotypes. These data suggest that normal embryonic lung growth, ASM differentiation and airway peristalsis are CFTR independent.

Airway ion transport impacts on disease presentation and severity in cystic fibrosis.

OBJECTIVES: Abnormal airway ion transport is a feature of cystic fibrosis. The aim of this study was to investigate whether distinct components of ion transport are associated with the clinical expression and severity of the disease. DESIGN AND METHODS: Univariate and multivariate analyses were used to study interaction effects between nasal potential difference parameters and clinical status, recorded at stable conditions, in 75 F508del homozygous young adults. RESULTS: All patients demonstrated increased sodium and reduced chloride conductances. Less sodium transport abnormalities were related to better respiratory function and nutrition. Presentation with digestive symptoms at diagnosis was associated with lower chloride conductance. With an accuracy of 85% good nutritional status was linked to more preserved lung function, increasing age and more preserved chloride conductance. CONCLUSIONS: Ion transport abnormalities have distinct clinical outcomes. Sodium conductance relates to respiratory function and nutrition; chloride conductance to nutrition and presentation with digestive symptoms at diagnosis.

Electrical potential difference across the nasal epithelium is reduced in premature infants with chronic lung disease but is not associated with lower airway inflammation.

Airway liquid content and insufficient absorptive airway ion transport at birth are potentially important factors in the development and severity of neonatal respiratory disease. The role of deficient absorptive airway ion transport in the development of chronic lung disease of prematurity is unknown. Additionally, lung inflammatory mediators modulate airway ion transport. Their effect on preterm lung ion transport and absorptive capacity is not established. We performed serial nasal potential difference studies and broncho-alveolar lavage in preterm infants born less than 30 wk postmenstrual age over the first four postnatal weeks. Our study aims were to: 1) compare nasal potential difference between preterm infants developing chronic lung disease and babies of similar gestation who do not; and 2) examine for an association between airway inflammation and ion transport parameters. We found that potential difference across the nasal epithelium increased with gestation, remained low and unchanged in infants developing chronic lung disease over the first four postnatal weeks, was significantly lower at four weeks in chronic lung disease infants, and was not associated with lower airway inflammation at any time point. We conclude that infants with chronic lung disease postnatally have a persistently reduced absorptive airway ion transport capacity.

Tolerance and withdrawal in goldfish exposed to ethanol.

Acute ethanol exposure decreases regulated body temperature. Tolerance and dependence develop with continued exposure. Removal of ethanol following chronic exposure produces withdrawal. There is little information on the time course for the development of tolerance and disagreement about the presence of a rebound effect on body temperature during withdrawal. For tolerance, we monitored the selected temperature [T(sel)] of goldfish [Carassius auratus] for 8 h while they were exposed to one of three doses of ethanol. During the period from 90 to 150 min post-exposure, T(sel) was: control: 24.1+/-0.07 degrees C; 0.4% ethanol: 21.9+/-0.09 degrees C; 0.8% ethanol: 21.3+/-0.05 degrees C; 1.1% ethanol: 18.4+/-0.10 degrees C. The difference between control and experimental T(sel) decreased by the following amounts for the final 1.5 h in the gradient: 0.4% ethanol: 2.60+/-0.12 degrees C; 0.8% ethanol: 1.58+/-0.09 degrees C; 1.1% ethanol: 4.08+/-0.12 degrees C. At all 3 doses, tolerance proceeded in a stepwise manner rather than continuously. Temperature regulation during withdrawal was evaluated by maintaining the goldfish in 0.8% ethanol for three days and subsequently monitoring T(sel) in an ethanol-free temperature gradient for 36 h. During withdrawal there was no evidence for an effect on T(sel); experimental and control values were nearly identical.

Nasal airway ion transport and lung function in young people with cystic fibrosis.

There is strong evidence that abnormal airway ion transport is the primary defect that initiates the pathophysiology of lung disease in cystic fibrosis (CF). To examine the relationship between airway ion transport abnormality and severity of lung disease, we measured nasal potential difference in 51 young people with CF using a validated modified technique. There was no correlation between any component of the ion transport measurement and clinical condition (respiratory function, chest radiograph score, or Shwachman clinical score). Thirty subjects, homozygous for the DeltaF508 mutation, were divided into those above and those below average respiratory function for their age. There was no significant difference in any of the ion transport parameters between those with above and below average pulmonary function. Of the 51 subjects, 10 had significant hyperpolarization after perfusion with a zero Cl- solution (> 5 mV). This Cl- secretory capacity did not correlate with above average lung function. These data do not support the assertion that the extent of lung disease in CF reflects the degree of ion transport abnormality. We suggest that although an ion transport abnormality initiates lung disease, other factors (e.g., environmental and genetic modifiers) are more influential in determining disease severity.

Airway ion transport on the first postnatal day in infants delivered vaginally or by elective cesarean section.

To determine airway ion transport in term infants on the first day of postnatal life, and to test the hypothesis that infants born without labor have reduced sodium absorption, we measured nasal potential difference using a modified perfusion protocol suitable for newborn infants. We examined maximal stable baseline potential difference, the change after perfusion with 10(-4) M amiloride (Deltaamil), and the change after perfusion with a zero-chloride solution (Deltazero Cl-) in infants born after elective cesarean section (n = 21) or normal labor (n = 20). Maximal stable baseline potential difference was not different in the two cohorts (-24.0 mV, range -9 to -64 mV versus -25.5 mV, range -6 to -44 mV). The majority of infants in both cohorts showed a substantial fall in potential difference after amiloride perfusion, and there was little capacity for chloride secretion. These results demonstrate a fluid absorptive pattern in the airways on the first postnatal day. In these well infants, the ion transport phenotype was not dependent on the presence or absence of labor.