Second-messenger regulation of sodium transport in mammalian airway epithelia

1. Sodium absorption is the dominant ion transport process in conducting airways and is a major factor regulating the composition of airway surface liquid. However, little is known about the control of airway sodium transport by intracellular regulatory pathways. 2. In sheep tracheae and human bronchi mounted in Ussing chambers under short circuit conditions, the sodium current can be isolated by pretreating tissues with acetazolamide (100 microM) to inhibit bicarbonate secretion, bumetanide (100 microM) to inhibit chloride secretion and phloridzin (200 microM) to inhibit sodium-glucose cotransport. This sodium current consists of amiloride-sensitive (57%) and amiloride-insensitive (43%) components. 3. The regulation of the isolated sodium current by three second messenger pathways was studied using the calcium ionophore A23187 to elevate intracellular calcium, a combination of forskolin and the phosphodiesterase inhibitor zardaverine to elevate intracellular cyclic AMP, and the phorbol ester 12,13-phorbol dibutyrate (PDB) to stimulate protein kinase C. 4. In sheep trachea, A23187 produces a dose-related inhibition of the sodium current with maximal effect (38% of ISC) at 10 microM and IC50 1 microM. This response affects both the amiloride-sensitive and insensitive components of the sodium current and is not altered by prior stimulation of protein kinase C or elevation of intracellular cyclic AMP. In human bronchi, A23187 (10 microM) produced a significantly greater inhibition of ISC (68%), a response which was unaffected by prior treatment with PDB or forskolin-zardaverine. 5. In sheep trachea, stimulation of protein kinase C with PDB produced a dose-related inhibition of ISC maximal (56% of ISC) at 50 nM (IC50 7 nM). This response was abolished by amiloride (100 microM) pretreatment suggesting a selective effect on the amiloride-sensitive component of the sodium current. The response was not altered by prior elevation of intracellular calcium or cyclic AMP. PDB (10 nM) caused a similar inhibition of ISC in human bronchi (43%). The effect of PKC stimulation following pretreatment with A23187 was diminished in human bronchi. Elevating intracellular cyclic AMP did not alter this response. 6. Addition of forskolin (1 microM) together with the phosphodiesterase inhibitor zardaverine (100 microM) produced a mean 35-fold increase in intracellular cyclic AMP in sheep trachea. This was associated with a small, but significant, 6% transient increase in ISC followed by a significant 4% fall. Neither effect could be abolished by amiloride pretreatment. In human bronchi, a small decrease in ISC which could not be distinguished from that occurring in controls was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of a Ca(2+)-dependent anion channel from sheep tracheal epithelium incorporated into planar bilayers

1. Anion-selective channels from the apical membrane of respiratory epithelia are involved in the secretion of chloride into the airway lumen. In cystic fibrosis (CF) there is an abnormality of phosphorylation-regulated chloride transport in this tissue, whilst a calcium-dependent pathway appears to function normally. 2. Using incorporation of apical membrane vesicles into planar phospholipid bilayers, we have characterized the most commonly seen anion-selective channel from sheep tracheal epithelium. 3. In symmetrical 200 mM-NaCl solutions the channel showed rectification, with a chord conductance at negative voltages of 107 pS and at positive voltages of 67 pS. The channel characteristically demonstrated subconductance states at 1/3 and 3/4 of the fully open level. Selectivity for chloride over sodium was approximately 6:1. 4. The channel required a minimum of approximately 100 microM-calcium on the presumed cytoplasmic surface (cis) for opening events to be observed. Open probability (Po) of the fully open state was markedly voltage dependent, but little effect of voltage was seen on the 1/3 subconductance state. 5. The relative permeabilities of monovalent anions monitored under bi-ionic conditions gave the following sequence: NO3- greater than I- greater than Cl- = Br- much much greater than F-. The order of conductances in symmetrical solutions was Cl- = NO3- greater than Br- greater than I- much much greater than F-. 6. The chloride channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) produced a dose-related reduction in Po with a flickering block at 10-50 microM and complete block at higher concentrations. 7. ATP produced a dose-related reduction in Po with effects at 1 microM and complete closing at 1 mM. These effects were only seen with addition to the cis chamber. 8. The catalytic subunit of protein kinase A, either when incubated with vesicles prior to incorporation into bilayers, or when added directly to either chamber, produced no effect. 9. Channels with very similar properties were seen from transfected human tracheo-bronchial cells. 10. Recent whole-cell patch-clamp studies have suggested a distinct calcium-activated chloride current in secretory epithelia. The described channel has properties in common with this current and may be a candidate for its single-channel basis.

Pulmonary deposition of nebulised amiloride in cystic fibrosis: comparison of two nebulisers

BACKGROUND Preliminary evidence suggests that regular inhalation of nebulised amiloride reduces sputum viscoelasticity, increases the clearance of sputum by mucociliary mechanisms and by coughing and reduces the rate of deterioration in lung function in patients with cystic fibrosis. These effects depend on adequate delivery of amiloride to the airways. This study was performed to quantify and compare pulmonary deposition of amiloride produced by two different nebuliser systems. METHODS The pulmonary deposition of nebulised amiloride (1 mg in 3 ml saline) was measured in eight patients with cystic fibrosis when given via a jet (System 22 with CR 60 compressor) and an ultrasonic (Fisoneb) nebuliser. Human serum albumin labelled with technectium-99m was used as an indirect marker for amiloride and its deposition in the lung was detected with a gamma camera. RESULTS Amiloride inhalation caused no side effects or changes in spirometric indices. The mean (SD) total pulmonary amiloride deposition was 57 (24) micrograms with the System 22 and 103 (53) micrograms with the Fisoneb nebuliser. Pulmonary deposition was completed more rapidly with the Fisoneb (4-5 minutes) than with the System 22 nebuliser (7-8 minutes) and the Fisoneb was preferred by the patients. CONCLUSIONS Both nebulisers appeared to deliver adequate amounts of amiloride to the lungs, but treatment with the Fisoneb nebuliser was quicker, more efficient, and more acceptable to the patients. Of the two nebulisers assessed, the Fisoneb would be preferred for clinical trials.

Quality of life in lung cancer

The prognosis of a patient with lung cancer is poor and the quality is at least as important as the quantity of remaining life. Quality of life is a useful concept which is almost impossible to define but there are a number of important factors which contribute to it. Culture, religion, previous experience and the point of view of the individual all contribute to which of these factors are considered most important. Any quality of life assessment will, therefore, only apply to a defined community. The measurement of quality of life in cancer trials should concentrate on a few important categories such as physical symptoms, psychology and social factors and should be simple rather than comprehensive. In addition, a few frequent measures are better than an occasional comprehensive survey and ideally, both approaches should be combined and compared. Such measurements are most useful for comparative trials rather than for making an overall quality of life estimate. Finally, for routine clinical use outside clinical trials the quality of life index or the Karnofsky scale is recommended.

A randomised trial of planned versus as required chemotherapy in small cell lung cancer: a Cancer Research Campaign trial

In a study of chemotherapy as palliative treatment, 300 patients with untreated limited and extensive stage small cell lung cancer (SCLC), who did not have progressive disease after the first cycle of chemotherapy, were randomised to receive either regular 'planned' chemotherapy or chemotherapy given 'as required' (AR). All patients received the same chemotherapy: cyclophosphamide 1 gm m-2 i.v., vincristine 2 mg i.v., and etoposide 120 mg m-2 i.v. on day 1, and etoposide 100 mg b.d. orally on days 2 and 3. Planned chemotherapy was given regularly every 3 weeks. AR chemotherapy was given for tumour-related symptoms, or for radiological progression of disease. Both groups of patients were assessed every 3 weeks and a maximum of eight cycles of chemotherapy was given. A detailed quality of life assessment was made using daily diary cards. The median survival (MS) of patients given AR chemotherapy was not significantly worse than those receiving planned treatment [MS: Planned = 36 weeks (95% C.I. 32-40 weeks), AR = 32 weeks (95% C.I. 28-37 weeks) P = 0.960]. In the AR patients the median interval between treatments was 42 days. On average AR patients received half as much chemotherapy as planned patients. AR patients with a treatment-free interval (TFI) of more than 8 weeks between the first and second cycles of chemotherapy survived longer than those in whom this interval was less than 4 weeks; [MS: TFI greater than 8 = 47 weeks (95% C.I. 32-53 weeks); TFI less than 4 = 24 weeks (95% C.I. 17-34 weeks) P = 0.013]. Contrary to expectation, in the quality of life assessment the AR patients scored themselves as having more severe symptoms than patients receiving planned treatment. AR chemotherapy is a novel method of attempting to use cytotoxic drugs palliatively, which resulted in less drug treatment for approximately equivalent survival. However the palliative effect seen with as required treatment was less satisfactory than with planned chemotherapy.

BOOP and COP

BOOP and COP are essentially the same condition and represent one of many ways in which the lung may respond to an inflammatory stimulus. Some underlying causes of BOOP have been identified but in many cases no cause can be found. The clinical and radiological features are of a pneumonic illness that responds to corticosteroids rather than antibiotics, but as milder cases are being identified the clinical spectrum is widening. Most cases can be confidently diagnosed only by open lung biopsy, but bacteriological lavage and transbronchial biopsy followed by a trial of steroids may sometimes be considered.

Effect of heart-lung transplantation on airway potential difference in patients with and without cystic fibrosis

Measurement of the potential difference (PD) across the airways provides an indication of the viability and integrity of the lining epithelium. PD was recorded from the lower airways in "diseased controls" and in patients following heart-lung transplantation. Diseased controls showed a high PD centrally which fell (became less negative) peripherally (trachea -15.8 mV (SEM 1.0), lobar bronchi -12.6 mV (1.2), segmental bronchi -9.8 mV (1.2]. Following heart-lung transplantation (HLT) the profile of PD with airway size was altered in comparison to non-transplanted patients with reduced values in the large airways. Host tracheal values above the anastomosis were similarly reduced. Two episodes of rejection were associated with a lower mean airway PD; no significant changes were found with infection. In patients with cystic fibrosis (CF), values in the donor lung did not differ from those in non-CF transplanted patients up to one year following transplantation, although nasal PD in the host remained elevated. HLT selectively alters the PD profile only of larger airways, which may relate to the interruption of the bronchial arterial supply to these sites.

Effect of heart-lung transplantation on airway potential difference in patients with and without cystic fibrosis

Measurement of the potential difference (PD) across the airways provides an indication of the viability and integrity of the lining epithelium. PD was recorded from the lower airways in "diseased controls" and in patients following heart-lung transplantation. Diseased controls showed a high PD centrally which fell (became less negative) peripherally (trachea -15.8 mV (SEM 1.0), lobar bronchi -12.6 mV (1.2), segmental bronchi -9.8 mV (1.2]. Following heart-lung transplantation (HLT) the profile of PD with airway size was altered in comparison to non-transplanted patients with reduced values in the large airways. Host tracheal values above the anastomosis were similarly reduced. Two episodes of rejection were associated with a lower mean airway PD; no significant changes were found with infection. In patients with cystic fibrosis (CF), values in the donor lung did not differ from those in non-CF transplanted patients up to one year following transplantation, although nasal PD in the host remained elevated. HLT selectively alters the PD profile only of larger airways, which may relate to the interruption of the bronchial arterial supply to these sites.

Adult respiratory distress syndrome. Advances in diagnosis and ventilatory management

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Tracheal potential difference in the reserpine and isoproterenol rat models of cystic fibrosis

Basic research into cystic fibrosis (CF) has been hampered by the lack of a suitable animal model. Reserpinized or isoproterenol-treated rats have been proposed as models because they exhibit certain morphological and physiological features characteristic of CF. Recent evidence suggests that abnormal epithelial transport of Na+ [corrected] and Cl- may underlie pathogenesis, defects that may contribute to the markedly more negative transepithelial electrical potential differences (PD) recorded in CF airways compared with controls. To test the models further, we measured tracheal PD in vivo in treated rats (reserpinized - 6.9 mV, SEM 0.7 mV, n = 7; isoproterenol-treated -10.2 mV, SEM 1.5 mV, n = 12) and found it to be no different from that of controls (-8.7 mV, SEM 0.6 mV, n = 25). The animals did, however, demonstrate a reduced gain in body weight as well as increased submaxillary gland weight, which reflected an increased mucus content in the acini. These observations suggest that although the reserpinized or isoproterenol-treated rat may be useful in the study of the pathogenesis of exocrine disturbances in disease, their use as models for the effect of the basic defect of CF in the airways may be limited.

Nasal potential difference: a clinical diagnostic test for cystic fibrosis

Patients with cystic fibrosis (CF) demonstrate a markedly more negative potential difference (PD) across respiratory epithelia than normal or "diseased" controls. A technique is described for the measurement of nasal PD in both children and adults. 145 non-CF subjects showed a mean PD of -19.0 mV (range -2 to -36) in comparison to 60 patients with cystic fibrosis with mean of -46.0 mV (range -32 to -77). Amongst the latter group those with more severe disease had a more negative PD. Measurement of nasal PD is easily learnt and rapidly performed and may provide an additional means of diagnosis for CF.

Nasal potential difference: a clinical diagnostic test for cystic fibrosis

Patients with cystic fibrosis (CF) demonstrate a markedly more negative potential difference (PD) across respiratory epithelia than normal or "diseased" controls. A technique is described for the measurement of nasal PD in both children and adults. 145 non-CF subjects showed a mean PD of -19.0 mV (range -2 to -36) in comparison to 60 patients with cystic fibrosis with mean of -46.0 mV (range -32 to -77). Amongst the latter group those with more severe disease had a more negative PD. Measurement of nasal PD is easily learnt and rapidly performed and may provide an additional means of diagnosis for CF.

Effect of inhaled furosemide on metabisulfite- and methacholine-induced bronchoconstriction and nasal potential difference in asthmatic subjects

To evaluate the hypothesis that furosemide inhibits indirect bronchoconstrictor challenges by altering airway epithelial ion transport, we studied its effects on indirect bronchoconstriction induced by inhaled metabisulfite (MBS) and nasal potential difference (PD) in seven subjects with mild asthma. Its effect on direct bronchoconstriction by the inhaled muscarinic agonist methacholine (MC) was studied in six of these subjects. Each subject inhaled furosemide, 30 mg, in a randomized, double-blind, placebo-controlled fashion immediately before challenge with MBS (0.3 to 160 mg/ml in increasing doubling concentrations) and, in another study, MC (0.125 to 32 mg/ml) aerosols from a nebulizer attached to a dosimeter. PC20MBS and PC20MC, the concentration of each agent needed to lower FEV1 by 20%, were calculated by linear interpolation of the log dose-response curves. Furosemide had no effect on resting lung function, but it caused a significant threefold reduction in sensitivity to MBS (PC20MBS: GM +/- GSEM, 15.1 +/- 1.6 mg/ml after placebo and 40.7 +/- 1.7 mg/ml after furosemide; p less than 0.001) with a protective index of 64.8 +/- 10.7%. Furosemide caused no change in sensitivity to MC (PC20 MC:GM +/- GSEM, 2.37 +/- 1.61 mg/ml after placebo and 2.19 +/- 1.751 mg/ml after furosemide; NS). In a third study, furosemide, 30 mg, and placebo were inhaled through the nose in a randomized double-blind fashion immediately prior to inhalation of a PC20 concentration of MBS through the nose. Nasal PD was measured before and after placebo or furosemide, and again after MBS inhalation.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomised, double-blind, placebo-controlled trial of methotrexate in steroid-dependent asthma

69 patients with steroid-dependent asthma (mean daily prednisolone dose 14.2 [SD 6.1] mg) took part in a randomised, double-blind, placebo-controlled study of 24 weeks' treatment with methotrexate 15 mg weekly. The patients were seen every 4 weeks by the same physician, who reduced the daily prednisolone dose by 2.5 mg if the daily diary card variables and measurements of lung function were unchanged or improved. All other treatment remained unchanged. After 24 weeks of treatment the prednisolone dose had been reduced by a significantly greater proportion in the methotrexate than in the placebo group (50% vs 14%) and the reduction was not sustained after the study treatment stopped. There were substantial abnormalities in liver function tests in 5 of the 38 patients taking methotrexate.

Quality of life during chemotherapy for small cell lung cancer: assessment and use of a daily diary card in a randomized trial

Fifty-three patients who were taking part in a randomized trial of chemotherapy in small cell lung cancer (SCLC) were entered into a study of quality of life measurement using a daily diary card. Patients received either four or eight cycles of initial chemotherapy and daily records were scored, using a four point scale of nausea, sickness, appetite, sleep, mood, pain, activity and general well being. Two hundred and fifty-six of a possible 379 cards were returned (68% compliance). The first 31 patients took part in an assessment of the diary card where comparison was made with nurse ratings using the card, the EORTC questionnaire and the Spitzer quality of life index. These comparisons showed appropriate convergent and divergent validity and demonstrated the sensitivity of the diary card to short term changes compared with the other measures. In the randomized trial the diary card demonstrated a worsening of sickness and related variables as treatment continued. This spilled over into mood and general well being although physical variables of pain, sleep and activity were largely unaffected. Prophylactic cranial irradiation was associated with a transient increase in sickness and vomiting. The study shows that the diary card is an instrument sensitive to short term changes in quality of life and thus especially useful for comparing effects during the period of treatment.

Infection v. colonisation

The interaction between bacteria and the human respiratory tract is complex and while the concept of three states, namely sterility, colonisation, and infection is clinically convenient it is inevitably in oversimplification. Evidence from both clinical and laboratory observations has led to some ideas about the relationship between colonisation and infection and while these are helpful in defining the steps involved, the decision of whether and when to start new treatment remains one of clinical judgement. This article reviews the evidence from lung disease both in and out of an intensive care unit and attempts to define the frontier between infection and colonisation in different clinical settings.