Biomedical subjects

J C Mak

Publications and source records attributed to J C Mak.

At least 55 records · Page 3Linked to original sources

PubMed1994

Agonist-induced up-regulation of platelet-activating factor receptor messenger RNA in human monocytes.

Platelet-activating factor (PAF) is a potent inflammatory mediator and it actions are mediated via specific cell surface receptors which are coupled to G-proteins. PAF stimulates several functions in monocytes and may modulate the expression of its own receptor. To investigate the possible modulation of PAF receptor mRNA expression Northern blot analysis of total RNA from human monocytes was performed using the cDNA of human leukocyte PAF receptor as a probe. Following the addition of 100 nM PAF, there was a 2.0-fold increase in PAF receptor mRNA at 60 minutes after the stimulation, which was inhibited by pretreatment with the PAF receptor antagonist WEB 2086. This increase returned to control level at 120 and 180 min. The increase of PAF receptor mRNA was statistically significant for 10 nM to 1 microM of PAF, while 100 nM of lysoPAF did not increase PAF receptor mRNA levels. These results suggest that PAF receptor expression can be regulated by PAF itself at the transcriptional level.

Adult↗

PubMed1994

Modulation of airway smooth muscle beta-adrenoceptor function by a muscarinic agonist.

We have investigated the effect of a muscarinic agonist and protein kinase C (PKC) activation on beta-adrenoceptors and their coupling to adenylyl cyclase in bovine tracheal smooth muscle. There was a significant reduction in maximum binding capacity of [125I]iodocyanopindolol ([125I]ICYP) after exposure to carbachol and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). Similarly both carbachol and PMA inhibited the 5'-guanylylimidodiphosphate-induced shift in [125I]ICYP binding by isoproterenol and significantly decreased isoproterenol-induced cyclic AMP accumulation. A phorbol ester, 4 alpha-phorbol 12,13-didecanoate which does not activate PKC had no effect on beta-receptor binding or coupling. These results suggest that PKC activation directly via a phorbol ester and indirectly via muscarinic receptor stimulation may lead to reduction and uncoupling of beta-receptors in airway smooth muscle. We suggest that this mechanism may be relevant to the reduction in beta-receptor coupling in asthmatic airways as an effect of PKC activation by inflammatory mediators and neurotransmitters.

Adrenergic beta-Agonists↗

PubMed1994

Characterization of muscarinic receptor subtypes in pig airways: radioligand binding and northern blotting studies.

This study was undertaken to characterize the muscarinic receptor subtypes present in adult pig peripheral lung and airway smooth muscle. The binding of the nonselective muscarinic antagonist [N-methyl-3H]scopolamine ([3H]NMS) to pig airways showed a single class of binding sites with a maximum density of 172 and 450 fmol/mg protein in peripheral lung and airway smooth muscle, respectively. Unlike [3H]NMS, the M1-selective antagonist, [3H]telenzepine, recognized two populations of binding sites in peripheral lung. Approximately 14% of total [3H]telenzepine binding sites displayed high affinity [dissociation constant (Kd) = 0.95 nM], whereas the remaining sites showed low affinity (Kd = 14.2 nM). The high- and the low-affinity [3H]telenzepine binding sites displayed the pharmacological profile of M1 and M2 receptors, respectively. Heterogeneity of pig airways muscarinic receptor was also revealed by competitive binding experiments against [3H]NMS with the M2-selective antagonist methoctramine. This compound recognized 70 and 90% of total receptors with high affinity in airway smooth muscle (Ki = 4.44 nM) and peripheral lung (Ki = 9.82 nM), respectively. This result suggests that the dominant muscarinic receptor in pig airways is of the M2 subtype. Northern blot analysis demonstrated the presence of m1 and m2 mRNAs transcripts in peripheral lung and m2 and m3 mRNAs in airway smooth muscle with no evidence for m4 mRNA.

Animals↗

PubMed1994

Tumor necrosis factor-induced interleukin-8 expression in cultured human airway epithelial cells.

The effects of tumor necrosis factor-alpha (TNF-alpha) on interleukin-8 (IL-8) expression and generation were examined in primary cultured human airway epithelial cells (HAEC) and a human lung epithelial cell line (A549). TNF-alpha increased IL-8 mRNA and protein expression in HAEC in a concentration- and time-dependent manner and these effects were inhibited by dexamethasone (1 microM). There was no change in the stability of IL-8 mRNA, and a nuclear run-on assay confirmed that TNF-alpha increased IL-8 gene transcription. TNF-alpha-induced IL-8 mRNA expression showed a biphasic response in HAEC, with an early increase at 2 h followed by a sustained increase from 8 h, which was abolished by the addition of cycloheximide, suggesting that the synthesis of another protein was involved. A549 cells also increased IL-8 secretion and mRNA after incubation of TNF-alpha, with inhibition by dexamethasone. However, A549 cells showed only an early single peak. A549 cells showed a 250-fold increase in the generation of IL-8 immunoreactivity, whereas primary cultured HAEC showed only a threefold increase, suggesting that HAEC and A549 cells may respond to TNF-alpha in different ways. The sustained increase in IL-8 secretion due to an increase in gene transcription in response to TNF-alpha may be an important amplification step in inflammatory diseases of the airways.

Bronchi↗

PubMed1994

Long-term exposure to norepinephrine results in down-regulation and reduced mRNA expression of pulmonary beta-adrenergic receptors in guinea pigs.

We studied the down-regulation of beta 2-adrenoceptors in guinea pig lung after chronic exposure to a beta-agonist. Guinea pigs were exposed to either norepinephrine (NE) or vehicle for 7 days. The density and affinity of beta-adrenoceptors were determined by Scatchard analysis of [125I]cyanopindolol binding in a lung membrane preparation and beta 1- and beta 2-adrenoceptor subtypes were studied in the presence of 0.1 microM ICI 118,551, a selective beta 2-adrenoceptor antagonist, or 0.1 microM CGP 20712 A, a selective beta 1-adrenoceptor antagonist, respectively. beta 2-Adrenoceptor mRNA was examined by Northern blot analysis. The tissue distribution of beta 2-adrenoceptors and of beta 2-adrenoceptor mRNA in lung after NE infusion were determined using receptor autoradiography and in situ hybridization, respectively. The functional significance of the decrease in beta 2-adrenoceptor was tested by measuring the relaxation response to a beta 2-agonist in isolated parenchymal strips. NE treatment resulted in decreases of 75 +/- 9%, 84 +/- 4%, and 66 +/- 9% of total beta-, beta 1-, and beta 2-adrenoceptors in the lung, compared with control animals. The administration of NE had only minimal effects on the dissociation constant (Kd) of the receptor for the radioligand. beta 2-Adrenoceptors mRNA was decreased by 46 +/- 13% after NE treatment. There was a correspondence between the distribution of beta 2-adrenoceptors and beta 2-adrenoceptor mRNA localization in both control and NE-treated guinea pigs. NE treatment reduced alveolar beta 2-adrenoceptors by 70 +/- 3% and its mRNA expression by 78 +/- 5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Expression of platelet-activating factor receptor mRNA in human and guinea pig lung.

Platelet-activating factor (PAF) has been implicated in the pathogenesis of several inflammatory pulmonary diseases, and specific binding sites have been demonstrated in human and guinea pig lung membranes by radioligand binding experiments. Both human and guinea pig PAF receptors (PAFR) have recently been cloned. We have used molecular probes to study the gene expression of PAFR in human and animal lung and in situ hybridization to determine the distribution of PAFR mRNA in peripheral lung. Northern blot analysis of total lung RNA from human lung parenchyma, using a 1.1-kb SmaI-EcoRI fragment of human PAFR cDNA or a 0.9-kb SmaI-SmaI fragment of guinea pig PAFR cDNA, demonstrated the expression of PAFR mRNA in human lung, with a single transcript of 4 kb. There was a significant increase in PAFR mRNA in the lungs of asthmatic patients and a significant decrease in PAFR mRNA in the lungs of cigarette smokers compared with normal patients. Similarly, the expression of PAFR mRNA on guinea pig and rat lung was detected as a single transcript of 3 kb, using both guinea pig and human PAFR cDNA probes. A full-length 1.8-kb human leukocyte PAFR cDNA probe was used as the DNA template for producing 35S-labeled antisense and sense cRNA probes for use in in situ hybridization studies of human peripheral lung. These studies revealed high levels of PAFR mRNA hybridization in blood vessels, moderate levels of hybridization in alveolar walls and peripheral airway smooth muscle, but no specific signal in airway epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Characterization of [3H]Ba 679 BR, a slowly dissociating muscarinic antagonist, in human lung: radioligand binding and autoradiographic mapping.

Ba 679 BR [7(S)-(1 alpha, 2 beta, 4 beta, 5 alpha, 7 beta)-7-[(hydroxydi(2-thienyl) acetyl)oxy]-9,9-dimethyl-3-oxa-9-azoniatricyclo[3.3.1.0(2,4)]nonan e bromide] is a new long-acting muscarinic antagonist developed as a bronchodilator drug. In this study, we have evaluated its affinity, its selectively, and the distribution of its binding sites in human lung. [3H]Ba 679 BR binds to a homogeneous population of muscarinic receptors in human lung membranes, with affinities in the subnanomolar concentration range. Like ipratropium bromide, Ba 679 BR showed no selectivity in its interactions with rat cerebrocortical M1 receptors (labeled with [3H]telenzepine) or heart M2 and salivary gland M3 receptors [labeled with [N-methyl-3H]scopolamine ([3H)]. Ba 679 BR displayed 6-20-fold higher affinity, compared with ipratropium bromide. We also studied the rate of Ba 679 BR and ipratropium bromide dissociation from human lung muscarinic receptors, by monitoring [3H]NMS association. Unlike ipratropium bromide (100 nM), which dissociated so quickly that there was little difference in the [3H]NMS association, compared with vehicle-treated membranes, Ba 679 BR (1 nM) had a strong protective effect against [3H]NMS binding ( > 70%) that lasted for 90 min. Kinetic experiments conducted with [3H]Ba 679 BR confirmed the slow dissociation profile of this compound. The dissociation rate constant (k-1) for [3H]Ba 679 BR was 3.29 +/- 0.18 x 10(-3) min-1, corresponding to a half-life of the complex of 212 +/- 11 min. Autoradiographic studies revealed that [3H]Ba 679 BR binding sites were densely distributed in alveolar walls and submucosal glands. These results suggest that the slow dissociation profile of Ba 679 BR from human lung muscarinic receptors might be the underlying mechanism by which this drug achieves its long duration of action observed in functional tests.

Adolescent↗

PubMed1993

Differential down-regulation of pulmonary beta 1- and beta 2-adrenoceptor messenger RNA with prolonged in vivo infusion of isoprenaline.

The down-regulation by isoprenaline of beta 1 and beta 2-adrenoceptors in rat lung was investigated at the receptor protein and messenger RNA level. Rats were treated with either isoprenaline or vehicle for 2 h, 1 day and 7 days. Isoprenaline treatment resulted in significant decreases of both beta 1- and beta 2-adrenoceptor density after 1 day with maximal decreases of 65 +/- 7 and 65 +/- 5% for beta 1- and beta 2-adrenoceptors, respectively, at 7 days. The administration of isoprenaline had no effect on binding affinities of either beta 1 or beta 2-adrenoceptors. beta 1-Adrenoceptor mRNA was significantly decreased by 58 +/- 10, 73 +/- 4 and 51 +/- 11% at 2 h, 1 day and 7 days, respectively, after isoprenaline treatment. However, the beta 2-adrenoceptor mRNA was not changed at 2 h after treatment and was significantly decreased by 35 +/- 11 and 45 +/- 12% at 1 day and 7 days, respectively after treatment. This time course of beta 2-adrenoceptor mRNA correlated well with that of the transcription factor cyclic AMP response element binding protein-like DNA binding activity, determined by gel shift assay. These findings indicate the existence of distinct mechanisms for down-regulation of beta 1- and beta 2-adrenoceptors and suggest the involvement of cyclic AMP response element binding protein in the down-regulation of beta 2-adrenoceptors in rat lung.

Animals↗

PubMed1993

Visualization of muscarinic m4 mRNA and M4 receptor subtype in rabbit lung.

We have used in situ hybridization to study the localization of muscarinic receptor subtype mRNAs and compared this with the distribution of muscarinic receptor subtypes using receptor autoradiography in tissue sections of the rabbit lung. To localize muscarinic receptor subtype mRNAs, subtype-specific synthetic oligonucleotide probes or riboprobes were generated. Two muscarinic receptor mRNAs (m3 and m4) were detected. The m3 mRNA was expressed in high concentration in tracheal smooth muscle, epithelium and blood vessels and to a lesser extent in bronchiolar smooth muscle while the m4 mRNA was abundantly expressed in bronchiolar smooth muscle and alveolar walls. No expression of m1, m2 or m5 mRNAs was found in any lung structures. This was confirmed by Northern blot analysis which revealed only a single transcript of 3.6 kb for m4 mRNA in rabbit lung. With the exception of the airway epithelium and blood vessels, there was a correspondence between mRNA localization and the distribution of muscarinic receptor subtypes visualized by [3H](-)-quinuclidinyl benzilate ([3H]QNB) autoradiographically in the presence of relatively selective muscarinic subtype antagonists (M1-M3) and direct labelling with selective [3H]AF-DX 384. The significance and the reasons for the presence of m4 mRNA and M4 receptors in the rabbit lung are uncertain and warrant further investigation.

Animals↗

PubMed1993

Tachykinin control of ferret airways: mucus secretion, bronchoconstriction and receptor mapping.

The effects of synthetic tachykinin receptor agonists on mucus secretion by ferret trachea was determined in vitro in Ussing chambers using 35SO4 as a mucus marker and the synthetic peptides [Sar9,Met(O2)11]substance P (SarSP), [beta Ala8]neurokinin A-(4-10) and [MePhe7] neurokinin B which are selective for NK1, NK2 and NK3 tachykinin-receptors respectively. The bronchomotor effects of the same agonists were also studied in vitro and tachykinin receptors were localized by autoradiographic mapping. SarSP was the only synthetic agonist able to elicit a concentration-dependent increase in mucus secretion and was much more potent than SP. The EC50 for SarSP was 1.7 x 10(-6) M. Moreover, the maximal increase in release of 35SO4 produced by SarSP 10(-5) M was 95% of the increase produced by methacholine 10(-4) M indicating that this concentration of SarSP induced a near maximal secretory response. There was no significant difference in the secretory action of SP administered from the luminal or the submucosal side of the tissue. Only the NK2 agonist was able to produce a concentration-dependent contractility of bronchial ring preparations and its effect was relatively weak (EC50 6.4 x 10(-6) M). Capsaicin (10(-5) M) produced only a slight increase in tracheal mucus secretion (28 +/- 5%; n = 6) and was completely ineffective in inducing bronchoconstriction. Binding sites for [125I]-Bolton Hunter SP were more evident than sites for [125I]-NKA on submucosal glands and epithelium. In contrast, only binding sites to NKA could be observed over the smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

A new calcitonin-receptor-like sequence in rat pulmonary blood vessels.

1. Two rat clones have been isolated which are similar to known calcitonin-receptor sequences. One of these does not have the distribution expected of a calcitonin receptor. It is widely distributed, with extremely high levels of expression in the lung, where it is associated with the blood vessels. 2. This rat sequence may represent the receptor for calcitonin-gene-related peptide or islet amyloid polypeptide. Both have binding activity in the lung and are potent vasodilators. The gene represented by this sequence may therefore play an important role in the maintenance of vascular tone.

Amino Acid Sequence↗

PubMed1993

Characterization of guinea pig pulmonary neurokinin type 1 receptors using a novel antagonist ligand, [3H]FK888.

We have characterized the binding of a novel radioligand, [3H] FK888, to neurokinin (NK)1 receptors in guinea pig lung membranes and localized its binding in guinea pig lung sections by autoradiography. Lung membranes were incubated with [3H] FK888 at 25 degrees and the assays were terminated by rapid filtration; nonspecific binding was defined as binding in the presence of 1 microM concentrations of the nonpeptide NK1-selective antagonist CP-96,345. Kinetic analysis showed that specific binding of [3H] FK888 (approximately 70% of total binding) was rapid, reaching a plateau by 20 min, and that binding was reversed by addition of 1 microM CP-96,345, giving a kinetic Kd of 0.46 nM. Binding of [3H] FK888 was saturable at approximately 1 nM, and equilibrium binding analysis gave a Kd of 0.32 +/- 0.03 nM and a Bmax of 46.9 +/- 7.1 fmol/mg of protein (four experiments). In competition studies, substance P, CP-96,345, and FK888 competed for [3H] FK888 binding, but NKA, NKB, and NK2-selective antagonists such as SR48968 and L-659,877 did not. Guanosine-5'-O-(3-thio)triphosphate significantly shifted the competition curve for substance P competition against [3H]FK888 binding to a lower affinity state, confirming that NK1 receptors are coupled to a G protein. Autoradiographic mapping in cryostat sections of lung showed that [3H]FK888 binding was dense over smooth muscle of all airways, with moderate binding over epithelium of bronchi and bronchioles as well as submucosal glands of trachea. No significant labeling of blood vessels was observed. [3H]FK888 binds to NK1 receptors in guinea pig lung and may be a useful tool for studying the expression and regulation of NK1 receptors.

Animals↗

PubMed1992

A comparison of beta-adrenergic receptors and in vitro relaxant responses to isoproterenol in asthmatic airway smooth muscle.

In previous reports, we have documented decreased in vitro airway smooth muscle responses to isoproterenol (ISO) in fresh postmortem trachea and bronchus from subjects with fatal asthma. One hypothesis to explain this finding is a decrease in beta-adrenergic receptor (beta AR) numbers on airway smooth muscle. We have now examined the autoradiographic distribution and density of beta AR using [125I]iodocyanopindolol on sections of airway smooth muscle adjacent to those studied functionally. The results have been compared with "normal" trachea and bronchi obtained from persons dying suddenly of nonpulmonary causes. In both trachea and bronchi, there was a 2.8-fold and 2.5-fold increase in specific grain counts, respectively, over smooth muscle from asthmatic airways (n = 6) compared with that determined in normal airways (n = 4, P less than 0.01, unpaired t test). The affinity of the beta AR for the agonist ISO, as determined by competitive binding experiments with increasing concentrations of (-)-ISO on tissue sections, was increased in asthmatic bronchi (IC50 = 80 +/- 13 nM; n = 3) compared with normal bronchi (IC50 = 562 +/- 144 nM; n = 4, P less than 0.05). We conclude that beta AR-mediated relaxant abnormalities in airway smooth muscle in fatal asthma cannot be explained by a decrease in receptor number and, surprisingly, beta AR expression is increased.

Asthma↗

PubMed1992

Localization of muscarinic receptor subtype mRNAs in human lung.

m2 mRNA in airway smooth muscle; m3 mRNA in airway epithelium, airway smooth muscle, and submucosal glands. No detection of m4 and m5 mRNAs was observed in any cellular structures. The presence of various muscarinic receptor subtype mRNAs was confirmed by Northern blot analysis. Only human lung mRNA hybridized to the m1 probe giving a single 3.2 kb transcript. mRNA from the human cultured airway smooth muscle cells gave m2 and m3 hybridization bands of about 6.0 kb and 4.5 kb, respectively, while mRNA from the cultured airway epithelial cells gave only m3 hybridization band of 4.5 kb. With the exception of the airway epithelium, there was a good correlation between the distribution of mRNAs by in situ hybridization and the distribution of receptor subtypes by autoradiographic mapping. These results may have an important clinical implication, and also give rise to further investigation of gene regulation of pulmonary muscarinic receptor subtypes in health and disease.

Adult↗

PubMed1991

Autoradiographic visualization of bradykinin receptors in human and guinea pig lung.

High affinity [3H]bradykinin (BK) receptor binding sites have been identified in human and guinea pig lung sections by in vitro autoradiography. [3H]BK was incubated with tissue sections for 120 min at 25 degrees C and non-specific binding determined by incubating adjacent serial sections in the presence of unlabelled BK. In saturation experiments with guinea pig lung sections, a single class of high affinity binding sites was identified with an apparent dissociation constant (Kd) of 0.5 +/- 0.1 nM and a maximal binding capacity (Bmax) of 35.2 +/- 2.9 fmol/mg protein (n = 5). The binding of [3H]BK was inhibited by unlabelled BK and NPC 349 (a specific B2 antagonist) at IC50 of 2.7 +/- 0.4 and 87 +/- 9 nM (n = 3), respectively. In contrast, no inhibition was found at 1 microM for a variety of vasoactive peptides such substance P, calcitonin gene-related peptide, vasoactive intestinal peptide and des-Arg9-[Leu8]BK (a specific B1-antagonist). Autoradiography revealed that BK receptors were widely distributed in human and guinea pig lung, with dense labelling over bronchial and pulmonary blood vessels of all sizes and in the lamina propria immediately subjacent to the basal epithelial cell layer in large airways. Airway smooth muscle was sparsely labelled in large airways, but greater labelling in smaller airways. There was also detectable labelling over submucosal glands and nerve fibres in human intrapulmonary bronchi and over alveolar walls in both species. The high density of BK receptors on bronchial and pulmonary blood vessels indicate that BK may play an important role in the regulation of airway and pulmonary blood flow, as well as airway epithelial regulation.

Adult↗

PubMed1991

Localization of beta 2-adrenoceptor messenger RNA in human and rat lung using in situ hybridization: correlation with receptor autoradiography.

We have used in situ hybridization to study the localization of mRNA encoding the beta 2-adrenoceptor in tissue sections of the human and rat lung and compared this with the distribution of beta 2-receptor binding sites using receptor autoradiography. To localize beta 2-receptor mRNA, a [32P]labeled antisense RNA probe (riboprobe) was generated from human or rat beta 2-receptor cDNA. A similar distribution of beta 2-receptor mRNA was identified in both species. The highest intensity of beta 2-receptor mRNA was detected in smooth muscle of small airways, airway epithelium and pulmonary blood vessels. Lower intensity of beta 2-receptor mRNA was identified in smooth muscle of large airways, and alveolar epithelium (presumably type I and type II pneumocytes). No significant hybridization signal was detected in interstitial tissue. The specificity of the hybridization signal was confirmed with a sense probe (having identical sequence to the mRNA) and preincubation with RNase A, and by Northern blot analysis which revealed a single band of mRNA of 2.2 kb. There was a correspondence between mRNA localization and the distribution of beta 2-receptors visualized by [125I]iodocyanopindolol autoradiographically in the presence of CGP 20712 (a beta 1-selective antagonist). However, alveolar walls that showed a high beta 2-receptor density had relatively low levels of mRNA. This cellular heterogeneity may reflect differences in RNA stability or transcription rate in different lung cells. This approach opens up new options in the investigation of the regulation of pulmonary beta 2-receptor gene expression in health and disease.

Animals↗

PubMed1990

Autoradiographic mapping of calcitonin gene-related peptide receptors in human and guinea pig hearts.

Calcitonin gene-related peptide (CGRP) is a 37-amino acid peptide that is a potent coronary vasodilator. Although CGRP is found in high concentrations around coronary arteries, its precise function in the control of coronary vasomotor tone remains unclear. We studied the distribution of specific receptors for CGRP in guinea pig and human hearts and found that the highest concentration of specific receptors for CGRP was in the major coronary arteries, which is consistent with the hypothesis that CGRP is implicated in control of coronary vasomotor tone. Areas of coronary artery with atheroma contained significantly decreased (158 +/- 35 grains/1,000 microns 2 tissue, n = 3) binding sites compared with binding sites in normal arteries (266 +/- 10 grains/1,000 microns 2 tissue, n = 11; p less than 0.001, t test). The decrease in receptors for CGRP around atheroma may predispose these vessels to coronary spasm.

Animals↗

PubMed1990

Autoradiographic visualization of muscarinic receptor subtypes in human and guinea pig lung.

Muscarinic receptor subtypes have been localized in human and guinea pig lung sections by an autoradiographic technique, using [3H](-)quinuclidinyl benzilate [( 3H]QNB) and selective muscarinic antagonists. [3H]QNB was incubated with tissue sections for 90 min at 25 degrees C, and nonspecific binding was determined by incubating adjacent serial sections in the presence of 1 microM atropine. Binding to lung sections had the characterization expected for muscarinic receptors. Autoradiography revealed that muscarinic receptors were widely distributed in human lung, with dense labeling over submucosal glands and airway ganglia, and moderate labeling over nerves in intrapulmonary bronchi and of airway smooth muscle of large and small airways. In addition, alveolar walls were uniformly labeled. In guinea pig lung, labeling of airway smooth muscle was similar, but in contrast to human airways, epithelium was labeled but alveolar walls were not. The muscarinic receptors of human airway smooth muscle from large to small airways were entirely of the M3-subtype, whereas in guinea pig airway smooth muscle, the majority were the M3-subtype with a very small population of the M2-subtype present. In human bronchial submucosal glands, M1- and M3-subtypes appeared to coexist in the proportions of 36 and 64%, respectively. In human alveolar walls the muscarinic receptors were entirely of the M1-subtype, which is absent from the guinea pig lung. No M2-receptors were demonstrated in human lung. The localization of M1-receptors was confirmed by direct labeling with [3H]pirenzepine. With the exception of the alveolar walls in human lung, the localization of muscarinic receptor subtypes on structures in the lung is consistent with known functional studies.

Animals↗