The effects of temperature on the survival and development of the free living stages of twisted wireworm Haemonchus contortus rudolphi, 1803 of sheep and other ruminants

Summary The effects of temperature on the survival and development of Haemonchus contortus have been studied using agar cultures inoculated with pure cultures of Escherichia coli. The ova hatched and infective larvae developed at temperatures ranging from 10°C to 37°C, but 40°C was lethal in 20 hrs. The eggs require 72 to 90 hrs at 37°C; 81 to 93 hrs at 34°C; 83 to 96 hrs at 30°C; 98 to 106 hrs at 25°C; 116 to 134 hrs at 20°C and 312 to 360 hrs at 10°C to become infective larvae. The optimum temperature of the free living stages was considered to be 30°C. The time of development of the larvae to the infective stage was inversely proportional to the ambient temperature between the limits of 10°C and 37°C. The longevity in water of third stage larvae previously cultured at 30°C was studied at temperatures ranging from 25°C to 50°C and at room temperature. The largest period of survival was 141 days at 25°C; 120 days at 30°C; 65 days at 34°C; 27 days at 37°C; 116 days at 40°C; 5 days at 45°C and 45 min at 50°C. At room temperature the larvae survived for 105 days.     

The effects of whole body vibration and exercise on fibrinolysis in men

Whole body vibration (WBV) is a novel modality that has been demonstrated to enhance muscular and cardiovascular functions reported to increase fibrinolytic activity. The purpose of this study was to examine the fibrinolytic response to WBV and exercise in men. Twenty healthy males (23.8 ± 0.9 years, 25.6 ± 0.2 kg m⁻²) participated in the study. Each subject performed three trials in randomized order separated by 1 week: exercise (X), vibration (V) and vibration + exercise (VX). Exercise sessions consisted of 15 min of unloaded squatting at a rate of 20 per minute. Vibration sessions were conducted on a WBV platform vibrating for 15 min. Tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) were assessed at baseline and immediately after each condition. The increase in tPA activity was significantly greater in VX (0.87 ± 0.35 to 3.21 ± 1.06 IU ml⁻¹) compared to X (0.71 ± 0.36 to 2.4 ± 1.13 IU ml⁻¹) or V (0.83 ± 0.25 to 1.00 ± 0.37 IU ml⁻¹) conditions, and greater in the X condition compared to the V condition. PAI-1 activity decreased significantly more in the VX (6.54 ± 5.53 to 4.89 ± 4.13 IU ml⁻¹) and X (9.76 ± 8.19 to 7.48 ± 7.11 IU ml⁻¹) conditions compared to the V (5.68 ± 3.53 to 5.84 ± 3.52 IU ml⁻¹) condition. WBV does not augment fibrinolytic activity in healthy men. However, WBV combined with squatting exercise increases fibrinolytic activity more than exercise alone.     

A model for simulation and patient-specific visualization of the tissue volume of influence during brain microdialysis

Microdialysis can be used in parallel to deep brain stimulation (DBS) to relate biochemical changes to the clinical outcome. The aim of the study was to use the finite element method to predict the tissue volume of influence (TVI_max) and its cross-sectional radius (r _TVImax) when using brain microdialysis, and visualize the TVI_max in relation to patient anatomy. An equation based on Fick’s law was used to simulate the TVI_max. Factorial design and regression analysis were used to investigate the impact of the diffusion coefficient, tortuosity and loss rate on the r _TVImax. A calf brain tissue experiment was performed to further evaluate these parameters. The model was implemented with pre-(MRI) and post-(CT) operative patient images for simulation of the TVI_max for four patients undergoing microdialysis in parallel to DBS. Using physiologically relevant parameter values, the r _TVImax for analytes with a diffusion coefficient D = 7.5 × 10⁻⁶ cm²/s was estimated to 0.85 ± 0.25 mm. The simulations showed agreement with experimental data. Due to an implanted gold thread, the catheter positions were visible in the post-operative images. The TVI_max was visualized for each catheter. The biochemical changes could thereby be related to their anatomical origin, facilitating interpretation of results.     

The genetic control of contact sensitization to inorganic metal compounds in guinea-pigs

Only a proportion of outbred guinea-pigs can be sensitized to K₂Cr₂O₇, BeF₂ and HgCl₂. Inbred Strain II can be sensitized to K₂Cr₂O₇ and BeF₂, but not to HgCl₂. Inbred strain XIII can be sensitized to HgCl₂ but not to K₂Cr₂O₇ or BeF₂. The ability to become sensitized appears to be transmitted as a dominant characteristic which is not sex linked.     

Tolerance to acute hypoxia maximally increases in case of joint effect of normobaric hypoxia and permissive hypercapnia in rats

IntroductionWe studied the comparative efficacy of independent and combined effects of normobaric hypoxia (90 mmHg) and permissive hypercapnia (50 mmHg) in increasing the tolerance of rats to acute hypobaric hypoxia.MethodsWe determined the time to loss of pose and life duration as a measure to assess the degree of tolerance of animals to hypobaric hypoxia by exposing them to an altitude of 11,500 m (barometric = 180 mmHg).ResultsExposure to hypercapnic hypoxia increased the tolerance to acute hypobaric hypoxia compared to exposure to normobaric hypoxia or permissive hypercapnia alone.DiscussionThe positive effects of hypercapnia and hypercapnic hypoxia occurred after one exposure, and increasing the number of exposures proportionally increased the tolerance to acute hypobaric hypoxia. The effect of permissive hypercapnia on increasing the tolerance to acute hypobaric hypoxia was found to be significantly greater than that of exposure to normobaric hypoxia. Therefore, we propose that hypercapnia is the dominant factor in increasing tolerance to acute hypobaric hypoxia.ConclusionTolerance to acute hypoxia maximally increases in case of joint effect of normobaric hypoxia and permissive hypercapnia.     

Nitric oxide in responses of regional kidney perfusion to renal nerve stimulation and renal ischaemia

The mechanisms underlying the relative insensitivity of medullary blood flow (MBF) to sympathetic drive remain unknown. We tested the effects of nitric oxide synthase blockade on regional kidney perfusion responses to electrical renal nerve stimulation (RNS) in pentobarbitone-anaesthetized rabbits. Under control conditions, RNS reduced renal blood flow (RBF), cortical blood flow (CBF) and MBF in a frequency-dependent manner. MBF was always reduced less than CBF or RBF. N^G-nitro-l-arginine increased mean arterial pressure (31±3 mmHg), reduced RBF (–8±1 ml/min) and MBF (–33±6 units), enhanced responses to RNS of RBF (from –48±6% to –58±6% at 2 Hz), CBF (from –38±6% to –43±4% at 2 Hz) and, particularly at low frequencies, MBF (from +1±18% to –32±11% at 2 Hz) and potentiated the RBF hyperaemic response following RNS (by 27±6% at 4 Hz). When glyceryl trinitrate was co-infused with N^G-nitro-l-arginine to restore basal nitrergic tone, responses to RNS and the subsequent hyperaemia were indistinguishable from control. Since resting renovascular tone or perfusion pressure has little impact on MBF responses to RNS, these present observations suggest that NO contributes to the blunted MBF response to RNS. Paradoxically, NO seems to blunt renal hyperaemia following acute RNS-induced ischaemia.     

Supplement 1993 (no. 37) to the Kauffmann-White scheme

This supplement reports the characterization of 36 new Salmonella serovars recognized in 1993 by the WHO Collaborating Centre for Reference and Research on Salmonella: 26 were assigned to S. enterica subsp. enterica, 5 to subspecies salamae 1 to subspecies arizonae, 2 to subspecies diarizonae, 1 to subspecies houtenae and 1 to S. bongori.     

Preparation and inhibition of interceptive actions

Two experiments aimed to provide an estimate of the last moment at which visual information needs to be obtained in order for it to be used to initiate execution of an interceptive movement or to withhold execution of such a movement. In experiment 1, we sought to estimate the minimum time required to suppress the movement when the participants were first asked to intercept a moving target. In experiment 2, we sought to determine the minimum time required to initiate an interceptive movement when the participants were initially asked to keep stationary. Participants were trained to hit moving targets using movements of a pre-specified duration. This permitted an estimate of movement onset (MO) time. In both experiments the requirement to switch from one prepared course of action to the other was indicated by changing the colour of the moving target at times prior to the estimated MO. The results of the experiments showed that the decision to execute or suppress the interception must be made no less than about 200 ms before MO.

Susceptibility profile of Candida rugosa (Diutina rugosa) against antifungals and compounds of essential oils

Candida rugosa (recently reclassified Diutina rugosa) is an emerging pathogen affecting humans and animals. Candida resistance to existing drugs is an important factor to be monitored, as well as the need of researching alternatives to conventional antifungals. Here, we evaluated the in vitro effects of some antifungals and major components of essential oils by the broth microdilution method (CLSI M27-A3) against fifteen C. rugosa strains from animals isolated and molecular identificated. The results showed MIC₉₀ of: 0.125 μg/mL to ketoconazole and voriconazole, 0.25 μg/mL to micafungin, 0.5 μg/mL to anidulafungin, 1 μg/mL to caspofungin, 2 μg/mL to amphotericin B, itraconazole and flucytosin, 8 μg/mL to fluconazole, 16 μg/mL to nystatin and >128 μg/mL to terbinafine. The compounds carvacrol (MIC₉₀ 320 μg/mL), thimol (MIC₉₀ 320 μg/mL) and cinnamaldehyde (MIC₉₀ 160 μg/mL) demonstrated antifungal activity against the samples tested.     

The contribution of refractoriness to arrhythmic substrate in hypokalemic Langendorff-perfused murine hearts

The clinical effects of hypokalemia including action potential prolongation and arrhythmogenicity suppressible by lidocaine were reproduced in hypokalemic (3.0 mM K⁺) Langendorff-perfused murine hearts before and after exposure to lidocaine (10 μM). Novel limiting criteria for local and transmural, epicardial, and endocardial re-excitation involving action potential duration (at 90% repolarization, APD₉₀), ventricular effective refractory period (VERP), and transmural conduction time (Δlatency), where appropriate, were applied to normokalemic (5.2 mM K⁺) and hypokalemic hearts. Hypokalemia increased epicardial APD₉₀ from 46.6 ± 1.2 to 53.1 ± 0.7 ms yet decreased epicardial VERP from 41 ± 4 to 29 ± 1 ms, left endocardial APD₉₀ unchanged (58.2 ± 3.7 to 56.9 ± 4.0 ms) yet decreased endocardial VERP from 48 ± 4 to 29 ± 2 ms, and left Δlatency unchanged (1.6 ± 1.4 to 1.1 ± 1.1 ms; eight normokalemic and five hypokalemic hearts). These findings precisely matched computational predictions based on previous reports of altered ion channel gating and membrane hyperpolarization. Hypokalemia thus shifted all re-excitation criteria in the positive direction. In contrast, hypokalemia spared epicardial APD₉₀ (54.8 ± 2.7 to 60.6 ± 2.7 ms), epicardial VERP (84 ± 5 to 81 ± 7 ms), endocardial APD₉₀ (56.6 ± 4.2 to 63.7 ± 6.4 ms), endocardial VERP (80 ± 2 to 84 ± 4 ms), and Δlatency (12.5 ± 6.2 to 7.6 ± 3.4 ms; five hearts in each case) in lidocaine-treated hearts. Exposure to lidocaine thus consistently shifted all re-excitation criteria in the negative direction, again precisely agreeing with the arrhythmogenic findings. In contrast, established analyses invoking transmural dispersion of repolarization failed to account for any of these findings. We thus establish novel, more general, criteria predictive of arrhythmogenicity that may be particularly useful where APD₉₀ might diverge sharply from VERP.     

Erythropoietin acute reaction and haematological adaptations to short, intermittent hypobaric hypoxia

This study aimed to determine whether brief hypoxic stimuli in a hypobaric chamber are able to elicit erythropoietin (EPO) secretion, and to effectively stimulate erythropoiesis in the short term. In two different experiments, a set of haematological, biochemical, haemorheological, aerobic performance, and medical tests were performed in two groups of healthy subjects. In the first experiment, the mean plasma concentration of EPO ([EPO]) increased from 8.7 to 13.5 mU · ml⁻¹ (55.2%; P < 0.01) after 90 min of acute exposure at 540 hPa, and continued to rise until a peak was attained 3 h after the termination of hypoxia. In the second experiment, in which subjects were exposed to a simulated altitude of up to 5500 m (504 hPa) for 90 min, three times a week for 3 weeks, all haematological indicators of red cell mass increased significantly, reaching the highest mean values at the end of the programme or during the subsequent 2 weeks, including packed cell volume (from 42.5 to 45.1%; P < 0.01), red blood cell count (from 4.55 × 10⁶ to 4.86 × 10⁶ · l⁻¹; P < 0.01), reticulocytes (from 0.5 to 1.4%; P < 0.01), and haemoglobin concentration (from 14.3 to 16.2 g · dl⁻¹; P < 0.01), without an increase in blood viscosity. Arterial blood oxygen saturation during hypoxia was improved (from 60% to 78%; P < 0.05). Our most relevant finding is the ability to effectively stimulate erythropoiesis through brief intermittent hypoxic stimuli (90 min), in a short period of time (3 weeks), leading to a lower arterial blood desaturation in hypoxia. The proposed mechanism for these haematological and functional adaptations is the repeated triggering effect of EPO production caused by the intermittent hypoxic stimuli. Accepted: 15 December 1999     

Older cancer patients’ information and communication needs: What they want is what they get?

Objective

To evaluate what information and communication aspects older cancer patients (≥65) consider important in preparing for chemotherapy treatment (CT), the extent to which this corresponds with what oncology nurses consider important, and the extent to which nurses attend to these aspects during real-life educational visits in oncology.

Methods

The QUOTE^chemo was used to have patients (n = 116) and nurses (n = 123) rate the importance of 66 aspects of patient education. Subsequently, the implementation of these 66 aspects during videotaped nursing visits (n = 155) with older cancer patients receiving CT for the first time was examined.

Results

Older cancer patients attached most importance to ‘treatment-related information’, ‘rehabilitation information’, ‘affective communication’ and discussing ‘realistic expectations’. Nurses placed great importance to almost all aspects except to discussing ‘realistic expectations’. Discrepancies were found between expressed importance and the actual performance during the videotaped consultations, particularly in discussing realistic expectations, coping information, interpersonal communication, and tailored communication.

Conclusion

Results pointed to aspects that need improvement to ensure high quality patient education tailored to the patients’ needs.

Practice implications

To make sure older cancer patients’ needs are met, more attention should be paid to the development of interventions supporting both needs assessment and fulfillment.     

The responses of the catecholamines and β-endorphin to brief maximal exercise in man

Summary The responses to brief maximal exercise of 10 male subjects have been studied. During 30 s of exercise on a non-motorised treadmill, the mean power output (mean±SD) was 424.8±41.9 W, peak power 653.3±103.0 W and the distance covered was 167.3±9.7 m. In response to the exercise blood lactate concentrations increased from 0.60±0.26 to 13.46±1.71 mmol·l^–1 (p<0.001) and blood glucose concentrations from 4.25±0.45 to 5.59±0.67 mmol·l^–1 (p<0.001). The severe nature of the exercise is indicated by the fall in blood pH from 7.38±0.02 to 7.16±0.07 (p<0.001) and the estimated decrease in plasma volume of 11.5±3.4% (p<0.001). The plasma catecholamine concentrations increased from 2.2±0.6 to 13.4±6.4 nmol·l^–1 (p<0.001) and 0.2±0.2 to 1.4±0.6 nmol·l^–1 (p<0.001) for noradrenaline (NA) and adrenaline (AD) respectively. The plasma concentration of the opioid-endorphin increased in response to the exercise from <5.0 to 10.2±3.9 p mol·l^–1. The post-exercise AD concentrations correlated with those for lactate as well as with changes in pH and the decrease in plasma volume. Post-exercise-endorphin levels correlated with the peak speed attained during the sprint and the subjects peak power to weight ratio. These results suggest that the increases in plasma adrenaline are related to those factors that reflect the stress of the exercise and the contribution of anaerobic metabolism. In common with other situations that impose stress,-endorphin concentrations are also increased in response to brief maximal exercise.     

Evaluation of the inoculum effect of new antibiotics against carbapenem-resistant enterobacterales

ObjectivesNew antibiotics have been developed to treat multidrug-resistant Enterobacterales. We evaluated the impact of the inoculum size on minimal inhibitory concentrations (MICs) of recently commercialized antibiotics.MethodsWe focused on 40 clinical carbapenemase-producing Enterobacterales and evaluated the impact of the inoculum size on the MICs to cefiderocol and to new β-lactams/β-lactamase inhibitors (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam, and meropenem-vaborbactam) at usual and high inocula (10⁵ and 10⁷ CFU/mL, respectively).ResultsAt usual inoculum, 15% were resistant to cefiderocol (n = 6), 30% to meropenem-vaborbactam (n = 12), 42.5% to ceftazidime-avibactam (n = 17), 55% to imipenem-relebactam (n = 22), and 90% to ceftolozane-tazobactam (n = 36). At higher inoculum, a switch from susceptible to resistant category was observed for 88% (n = 30/34; CI, 71.6–96.2), 75% (n = 3/4; CI, 21.9–98.7), 72% (n = 13/18; CI, 46.4–89.3), 50% (n = 14/28; CI, 31.1–68.9), and 8.7% (n = 2/23; CI, 1.5–29.5) isolates regarding cefiderocol, ceftolozane-tazobactam, imipenem-relebactam, meropenem-vaborbactam, and ceftazidime-avibactam, respectively.DiscussionCefiderocol and meropenem-vaborbactam were the most efficient against carbapenemase-producing Enterobacterales at usual inoculum. When increasing inoculum to 10⁷ CFU/mL, all of the molecules were impacted, particularly cefiderocol and imipenem-relebactam, while others, such as ceftazidime-avibactam, remain mildly affected. Our in vitro results deserved to be confirmed in vivo.     

Diagnostic approach to encephalitis and meningoencephalitis in adult returning travellers

Background

Encephalitis and meningoencephalitis are severe, sometime life-threatening infections of the central nervous system. Travellers may be exposed to a variety of neurotropic pathogens.

Structural integrity of the substantia nigra and subthalamic nucleus predicts flexibility of instrumental learning in older-age individuals

Flexible instrumental learning is required to harness the appropriate behaviors to obtain rewards and to avoid punishments. The precise contribution of dopaminergic midbrain regions (substantia nigra/ventral tegmental area [SN/VTA]) to this form of behavioral adaptation remains unclear. Normal aging is associated with a variable loss of dopamine neurons in the SN/VTA. We therefore tested the relationship between flexible instrumental learning and midbrain structural integrity. We compared task performance on a probabilistic monetary go/no-go task, involving trial and error learning of: “go to win,” “no-go to win,” “go to avoid losing,” and “no-go to avoid losing” in 42 healthy older adults to previous behavioral data from 47 younger adults. Quantitative structural magnetization transfer images were obtained to index regional structural integrity. On average, both some younger and some older participants demonstrated a behavioral asymmetry whereby they were better at learning to act for reward (“go to win” > “no-go to win”), but better at learning not to act to avoid punishment (“no-go to avoid losing” > “go to avoid losing”). Older, but not younger, participants with greater structural integrity of the SN/VTA and the adjacent subthalamic nucleus could overcome this asymmetry. We show that interindividual variability among healthy older adults of the structural integrity within the SN/VTA and subthalamic nucleus relates to effective acquisition of competing instrumental responses.     

Influence of gastric acid on susceptibility to infection with ingested bacterial pathogens

Despite the widely held belief that gastric acid serves as a barrier to bacterial pathogens, there are almost no experimental data to support this hypothesis. We have developed a mouse model to quantify the effectiveness of gastric acid in mediating resistance to infection with ingested bacteria. Mice that were constitutively hypochlorhydric due to a mutation in a gastric H⁺/K⁺-ATPase (proton pump) gene were infected with Yersinia enterocolitica, Salmonella enterica serovar Typhimurium, Citrobacter rodentium, or Clostridium perfringens cells or spores. Significantly greater numbers of Yersinia, Salmonella, and Citrobacter cells (P ≤ 0.006) and Clostridium spores (P = 0.02) survived in hypochlorhydric mice, resulting in reduced median infectious doses. Experiments involving intraperitoneal infection or infection of mice treated with antacids indicated that the increased sensitivity of hypochlorhydric mice to infection was entirely due to the absence of stomach acid. Apart from establishing the role of gastric acid in nonspecific immunity to ingested bacterial pathogens, our model provides an excellent system with which to investigate the effects of hypochlorhydria on susceptibility to infection and to evaluate the in vivo susceptibility to gastric acid of orally administered therapies, such as vaccines and probiotics.     

Short-term effects of oral enoximone on hemodynamics,exercise capacity,anaerobic threshold,and arrhythmias in congestive heart failure

Summary Enoximone, a phosphodiesterase-inhibitor, is a potent inotropic vasodilator agent that causes a marked improvement in hemodynamics in patients with congestive heart failure. The acute effects of oral enoximone on rest and exercise hemodynamics, ejection fraction, aerobic metabolism, exercise capacity, and arrhythmias were studied in 11 patients with moderate to moderately severe dilative cardiomyopathy after 8 days of enoximone (100 mg tid) in addition to baseline therapy (diuretics and digitalis).The cardiac index increased from 2.44±0.45 to 2.72±0.50 l/min/m² (p<0.01) at rest and from 4.00±0.96 to 4.75±0.95 l/min/m² (p<0.005) during exercise. Pulmonary wedge pressure decreased from 16.8±7.3 to 12.5±6.5 mmHg (p<0.005) at rest and from 28.2±8.0 to 24.5±10.3 mmHg (p< 0.05) during exercise. Systemic vascular resistance decreased from 1608±243 to 1495±300 dynes*sec*cm^–5 (p<0.05) at rest and from 1152±155 to 1027±236 dynes*sec*cm^–5 (ns) during exercise. The anaerobic threshold, which was recorded simultaneously, increased from 13.2±2.7 to 15.5± 2.5ml/kg/min VO₂ (p<0.02). The radionuclide ventriculography ejection fraction improved from 21.7±5.0 to 28.1±9.1% (p<0.01) during exercise; the changes at rest were not significant (20.8±6.2 vs 25.8±8.4%). Exercise tolerance showed an increase of 16% (492±133 to 573±135 sec, p< 0.005). The resting heart rate remained unchanged (81.8±13.4 vs 81.8±11.9). Interestingly, 24-h Holter monitoring revealed more or new repetitive arrhythmias in 9/11 patients.Short-term therapy with oral enoximone enhances ventricular performance by increasing cardiac contractility and lowering vascular resistance, both of which extend exercise tolerance and improve aerobic metabolism. Potential proarrhythmic effects need further evaluation, however.Abbreviations AMP adenosine monophosphate - PDE phosphodiesterase - VCO₂ carbon dioxide production - VPB ventricular premature beat - VE minute ventilation - VO₂ oxygen uptake Dedicated to Professor Jahrmärker on the occasion of his seventieth birthday     

Effect of dehydration and rapid rehydration on renal function and on plasma renin and aldosterone levels in the black Bedouin goat

Bedouin goats in the extreme deserts of the Middle East are regularly subjected to severe dehydration and possess a capacity to rapidly rehydrate by drinking large volumes of water. Urine flow, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in the fully hydrated animals amounted to 0.74±0.4 ml · min^–1, 76±29 ml · min^–1 and 344±146 ml · min^–1 respectively. In goats that were dehydrated to a loss of about 30% of their initial body weight, urine flow dropped to 24% of the value recorded in the hydrated animals and GFR and ERPF dropped to half their level recorded in the hydrated phase. Na and K⁺ excretion decreased in the water depleted goats and further decrease was recorded following drinking. Following drinking the urine flow, GFR and ERPF of the recently rehydrated goats dropped to below the rates recorded in the dehydrated animals. During the 3 h of the continuous recording that followed the drinking, all three rates did not exceed the predrinking level. Plasma renin activity amounted to 0.37±0.32 ng AI·ml^–1·h^–1 in the hydrated animals. In dehydrated ones it amounted to 4.8±2.8 ng AI·ml^–1·h^–1 and a further increase was recorded following drinking. Aldosterone in the hydrated goats was 5.5±4.3 ng% and increased to 13.9±2.3 ng% in the dehydrated animal and amounted to 20.1±5.5 ng% 2 h following drinking. It is concluded that the kidney in the Bedouin goat plays a major role in conserving both water and solutes, not only when deprived of water but also following its rapid rehydration.     

Permeability properties of cell membranes and tight junctions of normal and cystic fibrosis sweat ducts

The transepithelial permeability properties to Na, K, and Cl in microperfused segments of human eccrine sweat ducts from normal (N) subjects and patients with cystic fibrosis (CF) were examined. Amiloride administered on the luminal surface caused the transepithelial potential (V _t ) of normal ducts to depolarize to 0 mV, but in the absence of Cl in the medium or in CF ducts, amiloride caused theV _t to significantly reverse electrical polarity from lumen negative to lumen positive with respect to the serosal bath. TheV _t responses to changes in Na concentration in the lumen and K concentration in the bath were similar in CF and N ducts and showed that the basolateral membrane of the duct is K permeable and the apical membrane (in the absence of an anion shunt) is an almost ideal Na electrode. TheV _t of N ducts was insensitive to 10-fold changes in luminal K and contraluminal Na solution concentrations. These responses show that in normal ducts, the apical membrane and tight junctions are relatively impermeable to K, and the basal membrane and tight junctions are relatively impermeable to Na. TheV _t was highly sensitive to Cl^– changes on either surface before or after ouabain inhibition in N ducts, but in every case were insensitive to Cl^– changes in CF ducts. By comparison to control ducts the cation selective properties of the CF duct are probably normal, but both cell membranes as well as the tight junctions of the CF duct are relatively impermeable to Cl. The present data are inconclusive as to whether the route of Cl movement across the N duct epithelium is trans- or paracellular.