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Biomedical subjects

P M Barker

Publications and source records attributed to P M Barker.

At least 19 recordsLinked to original sources
PubMed2000

Macrolide antibiotics for cystic fibrosis.

BACKGROUND: Cystic Fibrosis is characterised by chest infection, the antibiotic treatment of which has significantly improved the outlook for people with this condition. The unusual nature of organisms that infect the chest of individuals with cystic fibrosis has restricted antibiotic choice. In particular the bacteria, Pseudomonas aeruginosa, is resistant to nearly all antibiotics that can be taken by mouth. There is laboratory evidence and evidence from other disease processes that macrolide antibiotics, whilst not directly active against Pseudomonas aeruginosa, may have indirect actions against this bacteria. OBJECTIVES: This review aimed to test the hypotheses that macrolide antibiotics; 1) Improve clinical status compared to placebo or another antibiotic 2) do not have unacceptable adverse effects If benefit was demonstrated, we aimed to assess the optimal type, dose and duration of macrolide therapy. SEARCH STRATEGY: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group specialist trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. In addition, Principal Investigators, known to work in the field and previous authors were contacted for unpublished or follow up data. Pharmaceutical companies, that manufacture macrolide antibiotics, were approached. SELECTION CRITERIA: Randomised controlled trials, published or unpublished, of macrolide compared to placebo, another class of antibiotic or another macrolide. Studies which compare regimes of the same macrolide at different doses will also be included. DATA COLLECTION AND ANALYSIS: No completed randomised controlled trials were identified. MAIN RESULTS: Three open studies excluded. Four ongoing randomised controlled trials were identified. No completed randomised controlled trials were identified. REVIEWER'S CONCLUSIONS: At present, there are no randomised controlled trials to evaluate the use of macrolide antibiotics for the treatment of chest infection in people with cystic fibrosis. Such trials, with clear outcome measures, are needed to properly evaluate this potentially useful treatment for cystic fibrosis.

Anti-Bacterial Agents↗
PubMed1999

Salt restriction induces pseudohypoaldosteronism type 1 in mice expressing low levels of the beta-subunit of the amiloride-sensitive epithelial sodium channel.

The amiloride-sensitive epithelial sodium channel (ENaC) is a heteromultimer of three homologous subunits (alpha-, beta-, and gamma-subunits). To study the role of the beta-subunit in vivo, we analyzed mice in which the betaENaC gene locus was disrupted. These mice showed low levels of betaENaC mRNA expression in kidney (approximately 1%), lung (approximately 1%), and colon (approximately 4%). In homozygous mutant betaENaC mice, no betaENaC protein could be detected with immunofluorescent staining. At birth, there was a small delay in lung-liquid clearance that paralleled diminished amiloride-sensitive Na+ absorption in tracheal explants. With normal salt intake, these mice showed a normal growth rate. However, in vivo, adult betaENaC m/m mice exhibited a significantly reduced ENaC activity in colon and elevated plasma aldosterone levels, suggesting hypovolemia and pseudohypoaldosteronism type 1. This phenotype was clinically silent, as betaENaC m/m mice showed no weight loss, normal plasma Na+ and K+ concentrations, normal blood pressure, and a compensated metabolic acidosis. On low-salt diets, betaENaC-mutant mice developed clinical symptoms of an acute pseudohypoaldosteronism type 1 (weight loss, hyperkalemia, and decreased blood pressure), indicating that betaENaC is required for Na+ conservation during salt deprivation.

Aldosterone↗
PubMed1999

Quantitation and localization of ENaC subunit expression in fetal, newborn, and adult mouse lung.

The newborn lung is cleared of fetal liquid by active Na+ transport. The heterotrimeric (alpha, beta, gamma) epithelial Na+ channel, ENaC, mediates this process. To understand the role of individual ENaC subunits in Na+ transport during development, we quantified murine ENaC (mENaC) subunit messenger RNA (mRNA) expression levels of fetal, neonatal, and adult mouse lung by Northern blot analysis and studied regional expression by in situ hybridization. alphamENaC and gammamENaC mRNA expression increased sharply in late fetal gestation and reached near-adult levels by Day 1 of postnatal life. betamENaC expression increased more gradually through late fetal and early postnatal life and increased progressively until adulthood. In situ hybridization studies showed similar localization patterns of alphamENaC and gammamENaC subunit expression in fetal and postnatal lung. gammamENaC and alphamENaC subunits were initially localized to fetal lung bud tubules and by late gestation both subunits were expressed in all regions (acinar and bronchiolar) of the distal lung epithelium. betamENaC was detected from 16 d gestation onward and was expressed most intensely in small airways. There was little expression of betamENaC in the alveolar region. In postnatal lung all three subunits were expressed intensely in small airways. In adult lung, alphamENaC and gammamENaC were expressed in a pattern consistent with an alveolar type II (ATII) cell distribution. The timing of quantitative changes in mENaC subunit expression is consistent with a role of Na+ transport in liquid clearance of the perinatal lung. Intense expression of mENaC subunits in medium and small airway epithelium and in ATII cells suggests that these regions are a primary location for liquid absorption in the perinatal and postnatal murine lung.

Age Factors↗
PubMed1998

Role of gammaENaC subunit in lung liquid clearance and electrolyte balance in newborn mice. Insights into perinatal adaptation and pseudohypoaldosteronism.

Genetic evidence supports a critical role for the epithelial sodium channel (ENaC) in both clearance of fetal lung liquid at birth and total body electrolyte homeostasis. Evidence from heterologous expression systems suggests that expression of the alphaENaC subunit is essential for channel function, whereas residual channel function can be measured in the absence of beta or gamma subunits. We generated mice without gammaENaC (gammaENaC -/-) to test the role of this subunit in neonatal lung liquid clearance and total body electrolyte balance. Relative to controls, gammaENaC (-/-) pups showed low urinary [K+] and high urinary [Na+] and died between 24 and 36 h, probably from hyperkalemia (gammaENaC -/- 18.3 mEq/l, control littermates 9.7 mEq/l). Newborn gammaENaC (-/-) mice cleared lung liquid more slowly than control littermates, but lung water at 12 h (wet/dry = 5.5) was nearly normal (wet/dry = 5.3). This study suggests that gammaENaC facilitates neonatal lung liquid clearance and is critical for renal Na+ and K+ transport, and that low level Na+ transport may be sufficient for perinatal lung liquid absorption but insufficient to maintain electrolyte balance by the distal nephron. The gammaENaC (-/-) newborn exhibits a phenotype that resembles the clinical manifestations of human neonatal PHA1.

Adaptation, Physiological↗
PubMed1998

Effects of adenosine, ATP, and UTP on chloride secretion by epithelia explanted from fetal rat lung.

Catecholamines trigger the switch from liquid secretion to absorption by perinatal lung, but regulation of Cl- and liquid secretion by pulmonary epithelia early in lung development (low [catecholamine]) is unknown. We looked for evidence for P1 and P2 receptors that mediate Cl- secretion in 14-d distal lungs and 14- and 18-d tracheas explanted from fetal rats (term = 22 d). We measured amiloride-insensitive transepithelial voltage changes induced by ATP, UTP, or adenosine. Explants were hyperpolarized by all three agonists and by terbutaline, a beta-adrenergic agonist and Cl- secretagogue. Whereas adenosine, ATP, or UTP injected into 14-d explant lumena, or adenosine added to the tracheal bath, induced hyperpolarization with EC50 of 2-15 microM EC50, values for all three agonists in the distal lung bath or ATP or UTP in the tracheal bath were five times greater. By 18 d, EC50 values for agonists in the bath were comparable to those for lumenal agonists (3-12 microM). In contrast, microinjection of terbutaline into all explant lumena (final concentration = 3 x 10(-5) M) induced minimal hyperpolarization, whereas the same concentration in the bath raised bioelectric potential difference maximally. We conclude that 1) beta-adrenergic receptors are present on the basolateral membranes of cells of the pulmonary epithelium early in lung development, and 2) adenosine, ATP, and UTP receptors are present in apical membranes throughout lung epithelial development, but basolateral receptors for these agonists in distal lung or ATP/UTP in trachea function later in gestation. The putative distribution of P1 and P2 receptors suggests a role for agonists released from pulmonary epithelial cells in the regulation of liquid secretion early in lung development.

Adenosine↗
PubMed1997

Decreased sodium ion absorption across nasal epithelium of very premature infants with respiratory distress syndrome.

OBJECTIVE AND STUDY DESIGN: Successful adaptation to air breathing at birth depends on rapid absorption of fetal lung liquid that is mediated by activation of amiloride-sensitive sodium ion channels. To test the relationship between respiratory epithelial Na+ transport and development of respiratory distress syndrome (RDS), we measured nasal transepithelial potential difference (PD) in 31 very premature (< or = 30 weeks of gestation) newborn infants. Infants were retrospectively assigned to RDS (22 infants) and non-RDS (9 infants) groups on the basis of clinical and chest x-ray criteria. RESULTS: Maximal nasal epithelial PD increased with birth weight (-1.2 mV/100 gm) and was lower in infants with RDS (-16.5 +/- 0.6 mV) than in those without RDS (-22.0 +/- 1.3 mV). Infants without RDS had PD values similar to normal fullterm infants. Amiloride inhibition of PD, an index of Na+ absorption, was significantly lower, within the first 24 hours of life, in infants in whom RDS developed (3.8 +/- 0.2 mV; 29.5% +/- 0.8% inhibition) than in those without RDS (6.1 +/- 0.6 mV; 38.6% +/- 0.5% inhibition). Maximal and amiloride-sensitive PD returned to normal during the recovery phase of RDS. CONCLUSIONS: We conclude that Na+ absorption across nasal epithelium increases with increasing birth weight and that impairment of Na+ absorption across the respiratory epithelia of very premature infants may contribute to the pathogenesis of RDS.

Amiloride↗
PubMed1996

Efficient adenovirus-mediated gene transfer to basal but not columnar cells of cartilaginous airway epithelia.

Adenoviral vectors (AdV) developed for treatment of the pulmonary manifestations of cystic fibrosis (CF) can deliver, with high efficiency, transgenes to respiratory epithelial cells grown in culture. This study investigated the efficiency of AdV-mediated gene transfer to murine and human respiratory epithelium in vivo and concluded that the epithelial cells facing the lumen of the respiratory cartilaginous airways (columnar cells) are poorly transduced with AdV. Mechanical injury to the epithelium, however, leads to efficient in vivo gene transfer by exposing a susceptible epithelial subtype (basal cells). Increased gene transfer efficiency in vivo after injury is not a nonspecific response because the proliferative status of the epithelium after injury was shown not to correlate temporally to the increased transduction susceptibility of the epithelium. Although basal cells were the cell type transduced at the time of vector delivery, with time, basal cell differentiation to columnar cells occurred with maintenance of transgene expression. Collectively, these results show that murine and human cartilaginous airways are poorly transduced by AdV. To correct the cartilaginous airway CF bioelectrical defect in vivo, efforts should be directed to increase the tropism of AdV to the columnar airway epithelial cells.

Adenoviridae↗
PubMed1995

Bioelectric properties of cultured monolayers from epithelium of distal human fetal lung.

Throughout intrauterine life, Cl(-)-rich liquid is secreted by the pulmonary epithelium. To evaluate the role of the most distal epithelium in liquid secretion, we measured bioelectric properties of monolayers composed of epithelial cells from acinar structures of postmortem human fetal lung (mean gestation, 22.3 wk; range, 18-24 wk). These monolayers formed high-resistance (R) barriers (mean R = 363 Ohm/cm2) when cultured in hormone-supplemented, serum-free medium. The transepithelial electrical potential difference (4.0 mV, lumen negative), was similar to that of whole fetal sheep lung in vivo. Equivalent short-circuit current (Ieq) was inhibited by apical amiloride (-20%), 5-(N-ethyl-N-isopropyl)-amiloride (-33 to -49%), or diphenylamine-2-carboxylate (DPC; -26%), and by basolateral ouabain (-77%), whereas apical 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) had no effect. Bumetanide added to the basolateral bath did not affect resting Ieq, but inhibited Ieq (-19%) in monolayers pretreated with apical amiloride, basolateral terbutaline, and apical ATP, and also inhibited Ieq (-22%) of monolayers pretreated with basolateral amiloride and DIDS. Ieq was stimulated by terbutaline (90-128%), ATP (70-186%), and ionomycin (141%). Stimulation of Ieq by these agents is compatible with induction of Cl- secretion through two pathways: channels that are opened by a rise in adenosine 3',5'-cyclic monophosphate, and channels that are opened by a rise in intracellular Ca2+. Inhibition of Ieq by apical DPC implies that Cl- secretion may contribute to basal Ieq.

Cell Membrane↗
PubMed1995

Cl- secretion by trachea of CFTR (+/-) and (-/-) fetal mouse.

The absence of pathologic changes in newborn cystic fibrosis (CF) lung suggests that the fetal CF lung is inflated with a normal volume of liquid and that Cl- is secreted through paths other than the cystic fibrosis transmembrane conductance regulator (CFTR)-associated Cl- channel. We studied liquid content of distal lung and transepithelial electrical potential difference (PD) of cultured cystic tracheal explants from 16 to 19 day gestation fetal mice of CFTR (+/-)(heterozygous) females that were mated with CFTR (-/-) "knockout" males. Distal lung water content was not affected by fetal genotype. Basal PDs were not different (CFTR (+/-), 8.6 mV, and CFTR (-/-), 9.1 mV), and PDs of both groups were inhibited by intraluminal injection of amiloride (10(-4) M) (-25%) and after addition of bumetanide (10(-4) M) to the bath (-40%). Terbutaline (3 x 10(-5) M) induced a similar increase in PD (about 65%) in both groups. Intraluminal injection of ionomycin (2 x 10(-5) and 5 x 10(-6) M) raised PD in both groups (CFTR (+/-) by 32 and 27% and CFTR (-/-) by 41 and 11%). All of the increase in PD induced by terbutaline and ionomycin was inhibited by bumetanide. The PD response to terbutaline was not attenuated by pretreatment with ionomycin or the Ca2+ chelator BAPTA (10(-4) M). Ionomycin or ATP, but not terbutaline, increased intracellular Ca2+ concentration of isolated cultured tracheal epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of hormones on potential difference and liquid balance across explants from proximal and distal fetal rat lung.

1. Fetal rat tracheas and lung buds form liquid-filled cysts in submersion culture. The volume that accumulates in cysts is driven by active Cl- secretion. 2. We examined the effects, on these explants, of hormones that induce liquid absorption by fetal sheep lung in vivo. Explants were impaled with microelectrodes to measure potential difference (PD). Liquid was estimated from explant weight. 3. Water/dry weight ratio of lung buds and tracheas after 8 days in culture averaged 12 and 22. Exposure of triiodothyronine (T3) and hydrocortisone (HC) followed by a physiological dose of adrenaline on day 7 for 24 h or by a maximal dose of terbutaline on day 8 for 4 h induced a 35% decrease in water/dry weight ratio of distal buds but not tracheas. No hormone, or combination of two hormones, affected the ratio for tracheas or lung buds. 4. Basal PDs of tracheas (18.9 mV) and lung buds (3.7 mV) were increased about 50% by terbutaline. The terbutaline response was inhibited by bumetanide, but not by amiloride injected into the cysts. 5. T3 and HC pretreatment reduced basal PD by one-third. Subsequent exposure to terbutaline raised the PD of hormone-pretreated lung buds by more than 150%, a response that was blocked by amiloride, but was antagonized minimally by bumetanide. Responses of hormone-pretreated tracheas were not different from those of untreated tracheas. 6. We conclude that: (a) absorption of liquid from lung buds is driven by an amiloride-sensitive process (active Na+ transport?) and (b) only distal lung contributes to the adrenaline-sensitive reabsorptive process required for perinatal adaptation to air breathing.

Adrenergic beta-Agonists↗
PubMed1993

Effect of gas composition on liquid secretion by explants of distal lung of fetal rat in submersion culture.

Throughout gestation, fetal lung is filled with liquid secreted by the pulmonary epithelium. Factors responsible for secretion and for induction of liquid absorption by postnatal lung are poorly understood. We studied effects of "fetal" (3% O2-8% CO2) and "postnatal" (21% O2-5% CO2) gas tensions and of low hormone concentrations [media with 10% charcoal-stripped fetal bovine serum (stFBS) or unstripped FBS] on water content and morphology of distal lung explanted from 14-, 20-, and 22-day fetal (term, 22 days) and 2-day neonatal rats and incubated in submersion culture. Water-to-dry weight ratios of freshly excised fetal whole lung at 20 (6.2) or 22 days (7.0) were greater than that of 2-day postnatal lung (4.7). Culture conditions did not affect water-to-dry weight ratio of cyst-forming 14-day explants (10.8) or acystic 2-day postnatal explants (2.4). Fetal gases and stFBS supported cyst formation in [and high water/dry weight (9.2, 12.6) of] 20- and 22-day explants. Cysts also formed in 20-day explants exposed to postnatal gases and stFBS (water/dry weight = 6.5). Other conditions resulted in minimal cyst formation by 20- and 22-day explants and in water/dry weight similar to that of freshly excised and drained distal lung from 22-day fetuses (2.1). Cysts were lined with cuboidal and thin epithelial cells. No cells were ciliated. We conclude that 1) secretion dominates liquid flow across epithelia of fetal rat lung until birth, 2) alveolar epithelium contributes to this secretion, and 3) liquid secretion by fetal distal lung late in gestation is regulated by gas composition.

Animals↗
PubMed1992

Liquid flow across the epithelium of the artificially perfused lung of fetal and postnatal sheep.

1. The lungs of five fetal (133-140 days gestation) and thirty-four postnatal (2-240 days) sheep were artificially perfused in situ with warmed and oxygenated sheep blood. In postnatal animals the airspace of the lung was filled with liquid similar in composition to fetal lung liquid. In fetal and postnatal animals luminal liquid volume was measured by the impermeant tracer technique. 2. Under resting conditions the pulmonary epithelium of fetal animals secreted liquid at a mean (+/- S.E.M.) rate of 2.0 (+/- 0.4) ml (kg body weight)-1 h-1, those of postnantal animals absorbed liquid at -1.8 (+/- 0.2) ml (kg body weight)-1 h-1. 3. Addition of 2,4-dinitrophenol to achieve a concentration of 1.5 x 10(-3) M in the perfusing blood in postnatal animals caused complete cessation of liquid absorption. 4. Light and electron microscopic examination of the lung after periods of up to 6 h of artificial perfusion showed no evidence of epithelial damage. From 3 h onwards, liquid accumulation was evident in the perivascular spaces. 5. Addition of adrenaline to the perfusate in fetal animals caused absorption of liquid to occur at a mean rate of -2.9 (+/- 1.3) ml (kg body weight)-1 h-1. In postnatal animals adrenaline caused the rate of liquid absorption to increase from a mean rate of -1.4 (+/- 0.2) to -2.2 (+/- 0.3) ml (kg body weight)-1 h-1. 6. In the fetus addition of amiloride (0.8 x 10(-4) M) to the luminal fluid blocked adrenaline-induced liquid absorption and caused secretion to occur at 1.3 (+/- 0.3) ml (kg body weight)-1 h-1. 7. In postnatal animals the response to amiloride was age dependent. In newborn lambs (2-14 days) amiloride blocked liquid absorption and caused secretion of liquid to occur in seven out of eight animals at a mean rate of 0.9 (+/- 0.3) ml (kg body weight)-1 h-1 (n = 8). In older animals (15-240 days) the characteristic response to amiloride was slowing of the rate of liquid absorption (mean rate of absorption,-0.2 (+/- 0.09) ml (kg body weight)-1 h-1, n = 18) with liquid secretion being seen in only three of eighteen animals.(ABSTRACT TRUNCATED AT 400 WORDS)

2,4-Dinitrophenol↗
PubMed1992

Bioelectric properties of cultured epithelial monolayers from distal lung of 18-day fetal rat.

In vivo studies of fetal sheep suggest that the liquid present in the lumen of the lung throughout fetal life is derived from Cl- secretion by the pulmonary epithelium. Monolayer preparations of enriched epithelial cells from distal fetal rat (18-day gestation) lung, grown in serum-free media, were histologically similar to acinar (prealveolar) structures of fresh tissue. In Ussing chambers, basal transepithelial potential difference (PD), calculated equivalent short-circuit current (Ieq), and transepithelial resistance (R) were 4.4 +/- 0.3 mV (matrix positive), 35.6 +/- 1.6 microA/cm2, and 120.0 +/- 4.0 omega cm2, respectively. Ouabain (10(-3) M) eliminated 57% of basal Ieq within 30 min, amiloride (10(-4) M) induced a 13% fall in Ieq, and phlorizin (10(-4) M) had no effect on bioelectric properties. Diphenylamine-2-carboxylate (DPC, 3 x 10(-3) M) inhibited Ieq by 50%. Bumetanide had no effect on baseline bioelectric parameters. The hyperpolarization that accompanied apical or bilateral replacement of Cl- and was enhanced by terbutaline suggested an apical Cl- permselectivity. Effects of Na+ replacement on amiloride-pretreated monolayers were consistent with Na(+)-dependent Cl- secretion or amiloride-insensitive pathways. Under these growth conditions, this preparation exhibits bioelectric characteristics that are compatible with Cl- secretion and Na+ absorption. The mechanism of Cl- secretion may be similar to that of airways but is uniquely bumetanide insensitive.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗