ADP release is the rate-limiting step of the MT activated ATPase of non-claret disjunctional and kinesin

The motor protein non-claret disjunctional (ncd) moves towards the minus ends of microtubules (MTs), whereas its close relative kinesin moves in the opposite direction towards the plus ends of MTs. The mechanisms of movement and directional reversal for these motor proteins are unknown. Here we report the rate constants for MT activated ADP release from a recombinant double-headed ncd protein, GST-MC5, and a recombinant double-headed kinesin protein, K delta 401, measured using the fluorescent nucleotide analogues methylanthranilyol ATP (mantATP) and mantADP. Comparison of the maximal MT activated mantADP release rates for these proteins with their maximal MT activated mantATP turnover rates indicates that ADP release is the rate-limiting step for ATP turnover for both ncd and kinesin. This data supports the view that directional reversal may result from structural rather than chemical kinetic differences in the way the motors interact with MTs.

Nucleotide-dependent angular change in kinesin motor domain bound to tubulin

Kinesin is a 'motor' molecule, consisting of two head domains, an alpha-helical coiled coil rod, and a tail part that binds to its cargo. When expressed in a bacterial system, the head domain is functional, and can bind to microtubules with the stoichiometry of one head per tubulin dimer. Kinesin moves along microtubules by means of a cyclic process of nucleotide binding, hydrolysis and product release. We have used negative-stain electron microscopy and image analysis to study the structures of microtubules and tubulin sheets decorated with the motor domain (head) of kinesin in three states: in the presence of an unhydrolysable ATP analogue, 5'-adenylylimidodiphosphate (AMP-PNP); without nucleotides; and with adenosine 5'-diphosphate (ADP). A single kinesin head bound to a microtubule has a pear-shaped structure, with the broader end towards the 'plus' end of the microtubule under all conditions; the reverse motor, ncd, is similarly oriented. Three-dimensional maps reveal that kinesin heads have a spike that is assumed to form the attachment to the tail of a complete kinesin molecule. This spike is perpendicular to the microtubule axis in the presence of ADP, but points towards the plus end (approximately 45 degrees) in the presence of AMP-PNP or absence of nucleotides. Our results provide direct evidence for a conformational change of the kinesin motor domain during the ATPase cycle.

Kinesin and ncd bind through a single head to microtubules and compete for a shared MT binding site

Kinesin and non claret disjunctional are closely related molecular motors that move in opposite directions along microtubules. We have used recombinant single-headed and double-headed constructs of both rat kinesin heavy chain and non claret disjunctional to investigate the interactions of these motor proteins with microtubules. At saturation the stoichiometry of binding for non claret disjunctional and kinesin to microtubules is one molecule (single or double-headed) per tubulin heterodimer. In the absence of added nucleotide, addition of increasing amounts of one motor results in the competitive displacement of the other motor from the microtubules. This effect is apparent also in the presence of the nucleotide analogue 5'-adenylimidodiphosphate, which tightens the binding of both kinesin and non claret disjunctional. Competition for binding sites occurs also under conditions of steady-state ATP turnover. We conclude that despite their opposite directionality, kinesin and non claret disjunctional compete for overlapping binding sites on the MT surface. Since the binding of the second head of a double-headed motor is sterically blocked, the data imply also that both kinesin and non claret disjunctional may translocate via a processive (alternating heads) mechanism with a minimum step size of approximately 8 nm.

The effect of intravenous phenylephrine on airway calibre in asthma

Tracheobronchial vasoconstriction and subsequent reduction of airway wall thickness due to the alpha 1-agonist methoxamine, might be responsible for prevention of exercise-induced asthma, and reduction of bronchial hyperresponsiveness to methacholine increase in exercise performance in patients with impaired left ventricular function. Since bronchial wall oedema plays an important role in asthma, we have now investigated the bronchial response to the intravenously administered alpha 1-agonist, phenylephrine, in asthma of various severity. Increasing noncumulative intravenous phenylephrine doses (100 to 600 micrograms) were injected in 18 asthmatic subjects (three groups: mild asthma, mild asthma with recent acute attack, severe obstructive asthma) and in 11 control subjects. Changes in specific airways resistance (sRaw) on phenylephrine were linearly related to the dose administered in 16 out of 18 asthmatic subjects, and in only 3 out of 11 control subjects. In the asthmatic subjects, sRaw increased in 10 patients whose asthma was mild, or bronchial obstruction mild to moderate, and decreased in the remaining 8 asthmatic subjects with more severe disease or with a higher degree of bronchial obstruction. Changes in forced expiratory volume in one second (FEV1) were consistent with those of sRaw. In the five asthmatic subjects who underwent the protocol twice, results were reproducible. There was no difference in the responses of heart rate between the three groups of asthmatic subjects. It is likely that phenylephrine acts both via airway smooth muscle contraction, an effect which might predominate in mild asthma, and via mucosal vasoconstriction, which might overcome the effect on smooth muscle in more severe asthma with bronchial wall oedema.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of intravenous phenylephrine on airway calibre in asthma

Tracheobronchial vasoconstriction and subsequent reduction of airway wall thickness due to the alpha 1-agonist methoxamine, might be responsible for prevention of exercise-induced asthma, and reduction of bronchial hyperresponsiveness to methacholine increase in exercise performance in patients with impaired left ventricular function. Since bronchial wall oedema plays an important role in asthma, we have now investigated the bronchial response to the intravenously administered alpha 1-agonist, phenylephrine, in asthma of various severity. Increasing noncumulative intravenous phenylephrine doses (100 to 600 micrograms) were injected in 18 asthmatic subjects (three groups: mild asthma, mild asthma with recent acute attack, severe obstructive asthma) and in 11 control subjects. Changes in specific airways resistance (sRaw) on phenylephrine were linearly related to the dose administered in 16 out of 18 asthmatic subjects, and in only 3 out of 11 control subjects. In the asthmatic subjects, sRaw increased in 10 patients whose asthma was mild, or bronchial obstruction mild to moderate, and decreased in the remaining 8 asthmatic subjects with more severe disease or with a higher degree of bronchial obstruction. Changes in forced expiratory volume in one second (FEV1) were consistent with those of sRaw. In the five asthmatic subjects who underwent the protocol twice, results were reproducible. There was no difference in the responses of heart rate between the three groups of asthmatic subjects. It is likely that phenylephrine acts both via airway smooth muscle contraction, an effect which might predominate in mild asthma, and via mucosal vasoconstriction, which might overcome the effect on smooth muscle in more severe asthma with bronchial wall oedema.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pretreatment with inhaled methoxamine on bronchial responses to histamine in asthmatic subjects

The underlying mechanisms of bronchial obstruction in asthma are complex. Both bronchospasm and bronchial oedema are thought to play pivotal roles in asthma, but their respective importance in a given asthmatic individual is unknown. To address this question, we assessed the effects of pretreatment with inhaled methoxamine, a potent alpha 1-adrenoceptor agonist, on bronchial response to inhaled histamine in 10 asthmatic subjects. The study was conducted according to a double-blind, cross-over, randomized and placebo-controlled design. In each subject, dose-response curves for the effects on forced expiratory volume in one second (FEV1) of serially doubling doses of inhaled histamine were obtained on three different days, 15 min after pretreatment with either methoxamine (10 mg) or duplicated placebo. Histamine, first dose 100 micrograms (543 nmol), was delivered by a breath-activated dosimeter every 5 min. FEV1 was measured in triplicate after each dose and the largest value was retained. There was no difference in baseline and prechallenge FEV1 after placebo and methoxamine. Mean coefficient of variation of decrease in FEV1 induced by histamine on the two placebo days was 6.7 +/- 2%. On average, the bronchial responses to histamine were not modified by pretreatment with methoxamine as compared to placebo (delta FEV1 = 0.83 +/- 0.14 l on methoxamine versus 0.85 +/- 0.11 l and 0.86 +/- 0.13 l on the two placebo days).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of substance P-induced microvascular leakage by inhaled methoxamine in rat airways

1. The effect of the inhaled alpha-adrenoceptor agonist, methoxamine (MTX), was studied on experimental airway oedema induced by injection of substance P (SP) in the rat. Sprague-Dawley rats (300-350 g) were anaesthetized with sodium thiopentone, tracheotomized and artificially ventilated. 2. MTX or its vehicle was administered by inhalation. Airway resistance and blood pressure were monitored continuously. Evans Blue dye (EB, 20 mg kg-1) was injected through a jugular catheter 1 min before SP (14.8 nmol kg-1). Airways were dissected out, weighed and placed in formamide for EB extraction and determination by spectrophotometry. 3. EB extravasation induced by SP was significantly reduced in distal intraparenchymal bronchi by inhaled MTX at doses of 50 micrograms kg-1 (58 +/- 9 vs 96 +/- 9 ng EB mg-1 tissue after vehicle, P < 0.001) and 100 micrograms kg-1 (69 +/- 11 vs 137 +/- 26 ng EB mg-1 tissue after vehicle, P < 0.01). Inhaled MTX by itself (100 micrograms kg-1) increased blood pressure: 172 +/- 6 vs 132 +/- 10 mmHg baseline (P < 0.02), but neither induced extravasation nor increased airway resistance. 4. In another set of experiments without SP, MTX was administered intravenously 1 min after EB. At 100 micrograms kg-1, i.v. MTX increased blood pressure to a similar extent as inhaled MTX (180 vs 147 mmHg baseline, P < 0.01), increased airway resistance and caused leakage of plasma proteins in distal intraparenchymal bronchi (79 +/- 7 vs 47 +/- 1 ng EB mg-1 tissue, P < 0.02). 5 Similarly, after sequential i.v. injections of doubling doses of MTX (50-800 microg kg-1), a marked EB extravasation was found in the airways. This was abrogated by pretreatment with prazosin (100 microg kg-1)but not with propranolol (2 mg kg-1).6 These results suggest that microvascular leakage and airway oedema induced by i.v. MTX may be linked to an increase in pressure in the pulmonary circulation, resulting from vasoconstriction of the pulmonary vasculature and acute cardiac dysfunction due to systemic hypertension.7 Our results with inhaled MTX show that direct deposition of MTX at the bronchial vasculature induces a reduction in SP-induced microvascular leakage in rat airways and that inhaled MTX does not share the untoward effect of i.v. MTX inducing airway oedema.

A simple and rapid micromethod for genomic DNA extraction from jugal epithelial cells. Application to human lymphocyte antigen typing in one large family of atopic/asthmatic probands

We describe a rapid and reliable micromethod for DNA isolation from buccal epithelial cells from the interior mouth mucosa. This convenient, noninvasive method could be applied to genetic typing in a small number of cells (about 2000 cells per cheek). We have shown that DNA released by this method is suitable for further amplification by polymerase chain reaction (PCR). Using this protocol, coupled with the PCR-RFLP (restriction fragment length polymorphism) method, we analyzed the allelic sequence diversity of the human lymphocyte antigen (HLA) class II genes in an extended family of 33 persons containing 14 asthmatic or atopic members. Six of eight DQA1 alleles, and 11 DQB1, 20 DPB1, and 10 DR haplotypes could be identified in a single DNA sample. Our results suggest that the DR53 group haplotype is frequently associated with allergic asthma and atopy. The micromethod described here may be useful in genetic epidemiology, especially in family studies involving small children.

Effect of furosemide on prostaglandin synthesis by human nasal and bronchial epithelial cells in culture

Inhaled furosemide protects asthmatic subjects against bronchial obstruction caused by indirect provocants. We have attempted to correlate the protective effect of furosemide with its ability to alter prostaglandin (PG) synthesis by the airway epithelium. Human epithelial cells from nasal polyps and bronchi were cultured in DME-Ham's F12 medium with 10% fetal calf serum. Confluent cells (days 6 through 8) were incubated for 30 min in fresh medium, and the PGs in the supernatant were measured by radioimmunoassay. Spontaneous output (ng.ml-1.mg-1 cell protein) was as follows (mean +/- SEM): PGE2 = 7.74 +/- 2.10 (n = 12), PGF2 alpha = 1.66 +/- 0.12 (n = 15), 6-keto-PGF1 alpha = 4.32 +/- 1.37 (n = 11), PGD2 = 0.73 +/- 0.16 (n = 11) for bronchial cells and PGE2 = 7.24 +/- 0.80 (n = 32), PGF2 alpha = 1.38 +/- 0.12 (n = 17), 6-keto-PGF1 alpha = 6.79 +/- 2.50 (n = 15), PGD2 = 0.42 +/- 0.07 (n = 17) for nasal cells. Incubation with arachidonic acid (25 micrograms/ml) for 30 min significantly increased the amounts of the four PGs. Incubation with furosemide (10(-4) M) for 30 min caused a marked reduction in both basal and arachidonic acid-stimulated production of PGE2 and PGF2 alpha but did not reduce production of 6-keto-PGF1 alpha and PGD2. Incubation with bumetanide (10(-4) M) for 30 min did not modify the PGE2 synthesis by nasal epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between use of the maximum tolerated dose and study sensitivity for detecting rodent carcinogenicity

The relationship between maximum tolerated dose (MTD) and study sensitivity for detecting rodent carcinogenicity was evaluated for 216 chemicals found to be carcinogens in laboratory animal studies conducted by the National Cancer Institute (NCI) and the National Toxicology Program (NTP). Approximately two-thirds of these rodent carcinogens would have been detected even without the top dose (estimated MTD), but in many of these studies, some site-specific carcinogenic effects would have been missed. Among the remaining one-third of the rodent carcinogens that required the top dose for statistical significance, approximately 80% had numerically elevated rates of the same site-specific tumors at lower doses as well. Only 13 of the NCI/NTP rodent carcinogens had increased tumor rates limited to the top dose for all sites of carcinogenicity. Alternatively, of the 838 site-specific carcinogenic effects observed in the NCI/NTP studies, 447 (53%) would have been detected even without the top dose. Of the remaining effects, 75% (294/391) showed numerically elevated site-specific tumor rates at lower doses. Our evaluation indicates that most carcinogenic effects observed at the top dose in rodent studies are also present (with reduced incidence that might or might not be statistically significant) at the lower doses typically employed (1/2MTD, 1/4MTD).

Origins of reversed directionality in the ncd molecular motor

The head or motor domain of the ncd (non-claret disjunctional) molecular motor is 41% identical to that of kinesin, yet moves along microtubules in the opposite direction to kinesin. We show here that despite the reversed directionality of ncd, its kinetics in solution are homologous in key respects to those of kinesin. The rate limiting step, ADP release, occurs at 0.0033 s-1 at 100 mM NaCl and is accelerated approximately 1000-fold when the motor binds to microtubules. Other reaction steps are all very fast (> 0.1 s-1) compared with ADP release, and the motor is consequently paused in the ncd.ADP state until microtubule binding occurs (Kd = 2 microM), at which point ADP release is triggered and the motor locks onto the microtubule in a rigor-like state. These data identify close functional homology between the strong binding states of kinesin and ncd, and in view of this we discuss a possible mechanism for directional reversal, in which the strong binding states of ncd and kinesin are functionally identical, but the weak binding states are biased in opposite directions.

HLA class II alleles in isocyanate-induced asthma

Studying genetic factors that control human immune responsiveness may further our understanding of specific types of asthma in which the role of immune factors is uncertain to date. HLA Class II gene products are involved in the control of immune responses. Therefore, we investigated whether HLA Class II genetic markers contribute to susceptibility or resistance to isocyanate-induced asthma (IAA) in exposed workers. We collected venous blood samples from two groups of unrelated white adults: (1) patients with isocyanate-induced asthma documented by a positive inhalation challenge; and (2) exposed individuals with no history of IAA. The second exon of DQA1, DQB1, DPB1, and DRB genes was selectively amplified by the polymerase chain reaction (PCR) method. HLA typing was carried out by the PCR-RFLP method, which allowed discrimination of most HLA DQA1, DQB1, DPB1, and DRB alleles. No significant difference was found in the distribution of DPB1 alleles between patients and control subjects. Allele DQB1*0503 and allelic combination DQB1*0201/0301 were associated with susceptibility to the disease. Conversely, allele DQB1*0501 and the DQA1*0101-DQB1*0501-DR1 haplotype conferred significant protection to exposed healthy control subjects. Our results are consistent with the hypothesis that immune mechanisms are involved in isocyanate-induced asthma and that specific genetic factors may increase or decrease the risk of developing IAA in exposed workers.

Locally deposited but not inhaled frusemide reduces nasal potential difference in healthy subjects

Previous publications suggest that prolonged inhalation of frusemide (F) does not cause a fall in the nasal transepithelial potential difference (PD) whereas locally deposited F does. In an attempt to reconcile these observations, we have measured the effect of inhalation through the nose and local deposition of F, amiloride (A), bumetanide (B) and salbutamol (S) on nasal PD in 7 healthy male volunteers in a randomised, double blind study. Solutions of drugs ranging from 10(-6) M to 10(-3) M (3 x 10(-8) M to 3 x 10(-5) M for B) in phosphate buffered saline 0.5 ml (PBS) were sequentially deposited in both nostrils, and nasal PD was measured 5 min after each dose. In 10 further volunteers, 10(-2) M solutions of A, F and S (3 x 10(-4) M for B) 5 ml were nebulised through the nose for 15 min, when nasal PD was measured. Resting PD was similar in the left and right nostrils averaging -17.1 mV (lumen negative). Placebo, inhaled of deposited B and S, and inhaled F did not change nasal PD. Topically deposited F significantly lowered PDmax in a dose-dependent manner [10(-4) M, -12% from baseline; 10(-3) M, -24%] as did the more potent A [10(-5) M, -19%; 10(-4) M, -31%; 10(-3) M, -47%]. Nebulised A (10(-2) M) had the same effect on nasal PD as deposited A (10(-4) M). The effects of locally deposited F and A (10(-3) M) on nasal PD were additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Modelling of passive expiration in patients with adult respiratory distress syndrome

The time-course of volume change during passive expiration preceded by an end-inspiratory hold was studied with a biexponential model in six adult respiratory distress syndrome (ARDS) patients. We measured the initial volumes and time constants of the fast (tau 1), and the slow (tau 2) compartments of expiration, as well as the static elastance of the respiratory system. The results were compared to those of 11 normal subjects. We observed that: 1) the biexponential model fitted closely the volume decay; 2) the fast compartment was responsible for 81 +/- 7% (ARDS) versus 84 +/- 10% (controls) of the total volume exhaled, with tau 1 = 0.35 +/- 0.11 s (ARDS) versus 0.50 +/- 0.22 s (controls); 3) the slow compartment contributed only 19 +/- 6% (ARDS) versus 16 +/- 7% (controls), with tau 2 = 4.67 +/- 2.38 s (ARDS) versus 3.27 +/- 1.54 s (controls); and 4) static elastance was higher in ARDS patients. The findings could be explained in terms of a four parameter viscoelastic model of the respiratory system.

Modelling of passive expiration in patients with adult respiratory distress syndrome

The time-course of volume change during passive expiration preceded by an end-inspiratory hold was studied with a biexponential model in six adult respiratory distress syndrome (ARDS) patients. We measured the initial volumes and time constants of the fast (tau 1), and the slow (tau 2) compartments of expiration, as well as the static elastance of the respiratory system. The results were compared to those of 11 normal subjects. We observed that: 1) the biexponential model fitted closely the volume decay; 2) the fast compartment was responsible for 81 +/- 7% (ARDS) versus 84 +/- 10% (controls) of the total volume exhaled, with tau 1 = 0.35 +/- 0.11 s (ARDS) versus 0.50 +/- 0.22 s (controls); 3) the slow compartment contributed only 19 +/- 6% (ARDS) versus 16 +/- 7% (controls), with tau 2 = 4.67 +/- 2.38 s (ARDS) versus 3.27 +/- 1.54 s (controls); and 4) static elastance was higher in ARDS patients. The findings could be explained in terms of a four parameter viscoelastic model of the respiratory system.

Structural and functional domains of the Drosophila ncd microtubule motor protein

Nonclaret disjunctional (ncd) is a kinesin-related microtubule motor protein that is required for proper chromosome distribution in Drosophila. Despite its sequence similarity to kinesin heavy chain, ncd translocates with the opposite polarity as kinesin, toward microtubule minus ends. We have expressed different regions of the protein in bacteria and analyzed the proteins for function. Results indicate that ncd consists of three domains: a basic, proline-rich N-terminal "tail," a central alpha-helical coiled-coil stalk, and a C-terminal motor domain. The ncd N terminus proteins bundle microtubules in motility assays and show ATP-independent binding to microtubules in solution. Truncated proteins, lacking the tail but containing the predicted motor domain and differing lengths of the stalk, did not support microtubule gliding in in vitro assays but showed microtubule-stimulated MgATPase activity in solution. Addition of a nonspecific N terminus to two of the truncated proteins restored directional gliding and rotation of microtubules in motility assays, demonstrating that these properties map to the predicted mechanochemical domain of ncd. Physical properties of the C terminus proteins indicate that the stalk region is important for dimerization and that the ncd protein probably exists and functions as a dimer.

Muscarinic receptors after syngeneic unilateral lung transplantation

We have characterized the muscarinic cholinergic receptor population by binding assay in left and right lung membranes from syngeneic Lewis rats one month after unilateral left lung transplantation and from controls. The density of muscarinic receptors measured by [3H](-)QNB binding was similar in left and right lung membranes one month after unilateral left lung transplantation (Bmax = 28.2 +/- 2.2 and 29.0 +/- 1.4 fmol/mg protein, respectively) and was similar between transplanted and control rats. Binding affinity also was similar on both sides (Kd = 28.5 +/- 9.5 and 32.3 +/- 2.7 pM, respectively). Binding parameters (Ki) of four selective muscarinic antagonists determined from competitive binding experiments of 0.5 nM [3H](-)QNB showed an order of potency: atropine > 4-DAMP > AF-DX 116 BS > pirenzepine both in transplanted and in control lungs. There was no significant difference in Ki values between left transplanted and right non transplanted lungs (1.8 +/- 0.1 and 1.9 +/- 0.1 nM; 4.3 +/- 0.5 and 3.5 +/- 0.5 nM; 80.9 +/- 13.8 and 78.9 +/- 18.8 nM; 480.4 +/- 40.9 and 481.7 +/- 78.2 nM, respectively for atropine, 4-DAMP, AF-DX 116 BS and pirenzepine). Values were also similar between transplanted and control lungs. These observations suggest a similar population of muscarinic receptors in the transplanted and the non transplanted lung in the Lewis rat. This result is in accordance with the similar physiological effect of exogenous acetylcholine that we previously observed in transplanted and non transplanted bronchi.

Modulation by theophylline and enprofylline of the excitatory non-cholinergic transmission in guinea-pig bronchi

The mechanism of action of xanthines in asthma remains controversial. Since sensory innervation may play a role in the pathogenesis of asthma, we investigated whether xanthines were capable of reducing the contractile response of the bronchi to nerve stimulation. In guinea-pig bronchi in vitro, electrical field stimulation (EFS: 40 V, 16 Hz, 0.2 ms during 10 s) induces a rapid cholinergic contraction followed by a long-lasting contraction due to a local release of neuropeptides from C-fibre endings. We measured isometric neuronally-mediated contractions of bronchial smooth muscle and studied the effects of increasing concentrations of two xanthine derivatives, theophylline, an antagonist of adenosine receptors, and enprofylline, which has no effect on adenosine receptors. Both enprofylline (1-50 microM) and theophylline (10-100 microM) inhibited, in a concentration-dependent manner, the peptidergic contraction, an effect which was more marked with enprofylline than theophylline (EC50 = 9.6 +/- 0.7 microM and 62.0 +/- 4.7 microM, respectively). Conversely, the cholinergic response was unaffected. Contractions induced by exogenous substance P (0.03-3 microM) were also unaffected by theophylline and enprofylline at the above mentioned EC50s. Our results suggest that concentrations of theophylline, similar to those used therapeutically, reduce the release of sensory neuropeptides from C-fibre endings. This effect is unrelated to adenosine receptor blockade, since enprofylline had a similar inhibitory effect.

Effect of airway blood flow on airflow

Resistance to gas flow of an airway is a function of both airway smooth muscle tone and thickness of the airway wall internal to the outer ring of airway smooth muscle. Schematically, the increase in airway resistance caused by shortening of airway smooth muscle may be potentiated by a concomitant increase in airway wall thickness caused by vasodilation of the bronchial vessels and/or microvascular leakage. Conversely, bronchial vasoconstriction may limit to some extent the increase in resistance to gas flow caused by airway smooth muscle shortening and/or congestion and edema of the airway wall. Many endogenous paracrine mediators, putatively involved in asthma and bronchial hyperresponsiveness, have both bronchomotor and vascular effects. The overall effects on resistance to airflow of endogenous or exogenous agents depend not only upon pre-existing airway smooth muscle tone and pre-existing condition of bronchial vessels but also upon two factors that facilitate microvascular leakage, namely, inflammation of the airway wall and outflow pressure of the bronchial circulation, which is close to left atrial pressure.

Modulation by theophylline and enprofylline of the excitatory non-cholinergic transmission in guinea-pig bronchi

The mechanism of action of xanthines in asthma remains controversial. Since sensory innervation may play a role in the pathogenesis of asthma, we investigated whether xanthines were capable of reducing the contractile response of the bronchi to nerve stimulation. In guinea-pig bronchi in vitro, electrical field stimulation (EFS: 40 V, 16 Hz, 0.2 ms during 10 s) induces a rapid cholinergic contraction followed by a long-lasting contraction due to a local release of neuropeptides from C-fibre endings. We measured isometric neuronally-mediated contractions of bronchial smooth muscle and studied the effects of increasing concentrations of two xanthine derivatives, theophylline, an antagonist of adenosine receptors, and enprofylline, which has no effect on adenosine receptors. Both enprofylline (1-50 microM) and theophylline (10-100 microM) inhibited, in a concentration-dependent manner, the peptidergic contraction, an effect which was more marked with enprofylline than theophylline (EC50 = 9.6 +/- 0.7 microM and 62.0 +/- 4.7 microM, respectively). Conversely, the cholinergic response was unaffected. Contractions induced by exogenous substance P (0.03-3 microM) were also unaffected by theophylline and enprofylline at the above mentioned EC50s. Our results suggest that concentrations of theophylline, similar to those used therapeutically, reduce the release of sensory neuropeptides from C-fibre endings. This effect is unrelated to adenosine receptor blockade, since enprofylline had a similar inhibitory effect.

Carboxypeptidase M-like enzyme modulates the noncholinergic bronchoconstrictor response in guinea pig

We studied the effects of aerosolized DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MGTA) (10(-4) M, 90 breaths), a specific inhibitor of carboxypeptidase B-type enzymes, on changes in total pulmonary resistance (RL) induced by aerosolized capsaicin (10(-7) to 10(-4) M; 10 breaths at each concentration) and vagus nerve stimulation (5 V, 5 ms, for 20 s at frequencies varying from 2 to 10 Hz) in anesthetized, atropinized, and ventilated guinea pigs. We also studied the effect of aerosolized MGTA on the bronchoconstrictor response to either aerosolized substance P, neurokinin A (10(-7) to 10(-4) M; 10 breaths at each concentration), and carbachol (10(-5) to 2 x 10(-4) M; 10 breaths at each concentration) or to i.v. administration of neurokinin A (10(-11) to 10(-8) mol/kg), bradykinin (10(-10) to 10(-7) mol/kg), and histamine (10(-8) to 10(-6) mol/kg). Although aerosolized MGTA caused no change in basal RL (P > 0.5), it did potentiate the noncholinergic bronchoconstrictor response to capsaicin (n = 5; P < 0.001) as well as to vagus nerve stimulation (n = 5; P = 0.001). In contrast, MGTA did not potentiate the bronchoconstrictor response to either aerosolized substance P, neurokinin A, and carbachol or to i.v. administration of neurokinin A, histamine, and bradykinin. Carboxypeptidase activity cleaving C-terminal arginine or lysine was found in the membrane preparations of trachea and lung from guinea pigs. The membrane-bound carboxypeptidase activity was maximal at pH 7.0 and was enhanced by the presence of CoCl2 (1 mM) in both the tracheal and lung tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Passive partitioning of respiratory volumes and time constants in ventilated patients

If the thoracoabdominal partitioning of volumes in the mechanical respiratory apparatus was constant, one transducer of indirect spirometry should be sufficient to measure volume variations. To verify this hypothesis we used respiratory inductive plethysmography (RIP) in 16 paralysed patients, of whom eight had normal lungs and 8 had not, to measure: 1) the thoracoabdominal partitioning of volumes (400-1,200 ml) insufflated from either a syringe (Syr) or a ventilator (Vent); and 2) thoracic (Tho) and abdominal (Abd) time constants (T0.368) on spontaneous deflation to barometric pressure. In eleven additional subjects with normal lungs we measured only the time constants. 1) Correlation coefficients of the calibration lines were in all but one subject > 0.98. In all patients the error of volume was < +/- 10% when either one of two coils alone was used to assess volumes with no difference between the two coils; 2) Partitioning varied little with volumes (4 +/- 2%), but widely between subjects, with no group average significant difference between Syr and Vent; 3) T0.368 were identical for Tho and Abd except in one patient; 4) Partitioning and T0.368 were volume size independent. We conclude that, to measure volume variations and time constants in ventilated, paralysed patients, the use of either a thoracic or abdominal single coil RIP is justified. We also provide the normal range for time constant in 19 subjects (0.73 +/- 0.29 s).

Passive partitioning of respiratory volumes and time constants in ventilated patients

If the thoracoabdominal partitioning of volumes in the mechanical respiratory apparatus was constant, one transducer of indirect spirometry should be sufficient to measure volume variations. To verify this hypothesis we used respiratory inductive plethysmography (RIP) in 16 paralysed patients, of whom eight had normal lungs and 8 had not, to measure: 1) the thoracoabdominal partitioning of volumes (400-1,200 ml) insufflated from either a syringe (Syr) or a ventilator (Vent); and 2) thoracic (Tho) and abdominal (Abd) time constants (T0.368) on spontaneous deflation to barometric pressure. In eleven additional subjects with normal lungs we measured only the time constants. 1) Correlation coefficients of the calibration lines were in all but one subject > 0.98. In all patients the error of volume was < +/- 10% when either one of two coils alone was used to assess volumes with no difference between the two coils; 2) Partitioning varied little with volumes (4 +/- 2%), but widely between subjects, with no group average significant difference between Syr and Vent; 3) T0.368 were identical for Tho and Abd except in one patient; 4) Partitioning and T0.368 were volume size independent. We conclude that, to measure volume variations and time constants in ventilated, paralysed patients, the use of either a thoracic or abdominal single coil RIP is justified. We also provide the normal range for time constant in 19 subjects (0.73 +/- 0.29 s).