Biomedical subjects

J C Mak

Publications and source records attributed to J C Mak.

60 records · Page 4Linked to original sources

PubMed1990

Cholinergic control of human airways in vitro following extrinsic denervation of the human respiratory tract by heart-lung transplantation.

In heart-lung transplantation (HLT), the airways have been assumed to be denervated since cholinergic, adrenergic, and sensory nerves are severed. Challenge studies of such patients suggest that there is an increase in airway responsiveness to inhaled cholinergic agonists, which may be explained by denervation hypersensitivity of muscarinic receptors on airway smooth muscle. We have studied the cholinergic control of airways from lungs removed from five patients (8 to 31 yr of age) undergoing retransplantation because of rejection-related bronchiolitis, with time since transplantation ranging from 12 to 32 months. These airways were compared with airways obtained from eight heart donors (24 to 42 yr of age) and from five patients undergoing surgical lobectomy for bronchial carcinoma (54 to 72 yr of age). Bronchial rings (distal lobar and subsegmental) were mounted in organ baths and isometric contractile responses measured. Contractile responses to acetylcholine (ACh, 10 nM to 10 mM) and to electrical field stimulation (EFS) (40 V, 0.5 ms, 1 to 64 Hz for 15 s) were determined. Transplant and control airways showed the same response to ACh, with mean EC50 values of 61.0 +/- 0.32 microM for HLT patients, 57.6 +/- 0.24 microM for donor patients, and 48.7 +/- 1.2 microM for lobectomy patients, suggesting no denervation hypersensitivity of muscarinic receptors. EFS, which activates postganglionic cholinergic nerves, caused similar frequency responses in both transplant and control airways, suggesting that postganglionic nerves are intact. [3H]quinuclidinyl benzilate binding to membranes prepared from lung was performed to determine muscarinic binding characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1990

Peripheral type benzodiazepine receptors in human and guinea pig lung: characterization and autoradiographic mapping.

Binding of [3H]Ro5-4864, a ligand selective for peripheral-type benzodiazepine receptors, to human and guinea pig lung membranes was characterized and the binding sites localized in lung sections by light microscopic autoradiography. Inhibition of [3H]Ro5-4864 binding by unlabeled Ro5-4864, PK11195, midazolam, diazepam, clonazepam and flumazenil indicated that [3H]Ro5-4864 bound to specific receptors and binding was reversible. Scatchard analysis indicated a single class of binding site, with a dissociation constant (Kd) of 12.8 +/- 2.1 nM with maximum binding capacity of 2.6 +/- 0.6 pmol/mg of protein for human lung and Kd of 8.4 +/- 1.5 nM and maximum binding capacity of 3.5 +/- 0.3 pmol/mg of protein for guinea pig lung. Autoradiograms showed specific labeling over discrete structures in both human and guinea pig lung. Labeling was particularly dense over submucosal glands in intrapulmonary bronchi of human. Airways were also labeled, with epithelium having a higher grain density than smooth muscle. Labeling over smooth muscle was denser in small compared to large airways. Vascular smooth muscle was not labeled in either human and guinea pig. The alveolar walls were uniformly labeled in both species. The functional significance of pulmonary peripheral-type benzodiazepine receptors remains to be determined.

Adult↗

PubMed1989

Muscarinic receptor subtypes in human and guinea pig lung.

Muscarinic receptor subtypes in human and guinea pig lung membranes were characterised using selective muscarinic antagonists. Competition experiments were carried out against [3H](-)-quinuclidinyl benzilate binding at 25 degrees C in Tris-HCl buffer; non-specific binding was determined in the presence of 1 microM atropine. Of all the antagonists examined, only the M1-selective antagonist pirenzepine exhibited a heterogeneous binding profile (nH less than 1.0), best described by two-binding sites of high and low affinity. Binding of [3H]pirenzepine confirmed the presence of a high proportion of high affinity (M1) receptors (60% of total) in human peripheral lung. The high potency of M3-selective antagonists 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP) and hexahydrosiladifenidol suggested the presence of M3 receptors, but the low potency of AF-DX 116 and methoctramine indicated that there was no significant population of M2 receptors present. The existence of muscarinic receptor subtypes in lung may have important clinical implication but their cellular localisation remains to be determined.

Adamantane↗

PubMed1989

Calcitonin gene-related peptide vasodilation of human pulmonary vessels.

Human calcitonin gene-related peptide (CGRP) is localized to sensory neurons in pulmonary vessels and is a potent vasodilator. We have characterized the effects of CGRP in human pulmonary vessels and localized the receptors for this peptide by autoradiography. Fresh human lung tissue was obtained from eight patients undergoing surgery and small (200-400 microns ID) pulmonary arteries and veins were dissected free of surrounding connective and pulmonary tissue. Pairs of vessels were studied and in one of each pair the endothelium was left intact and from the other of each pair the endothelium was removed by gentle abrasion. For functional studies arteries (n = 9) and veins (n = 9) were suspended in an organ bath, precontracted with 1 microM prostaglandin F2 alpha. CGRP (10 pM to 10 microM) was added in a cumulative manner. CGRP caused a dose-dependent relaxation of endothelium intact human pulmonary arteries and veins with log EC50 values of -8.01 +/- 0.35 and -8.70 +/- 0.40, respectively (not significant). Removal of the endothelium did not diminish the vasodilator potency of CGRP in either vessel. For autoradiographic studies, cryostat sections of the small human pulmonary vessels with or without endothelium were used. 125I-CGRP densely labeled CGRP receptors on vascular smooth muscle and endothelial removal did not have any effect on grain density. We concluded that CGRP is a potent vasodilator of human pulmonary arteries and veins that is not dependent on an intact endothelium. These functional studies correlate with the distribution of CGRP receptors as localized by autoradiography.

Adult↗

PubMed1988

Muscarinic receptor subtypes mediating vasodilation in the pulmonary artery.

Binding studies in several species have demonstrated a high proportion of M1 muscarinic receptors in the lung but their localization is uncertain. Using [3H]quinuclidinyl benzylate we have confirmed that binding sites with high affinity for pirenzepine account for 50% of muscarinic receptors in the rat lung. Our functional studies using the muscarinic antagonists 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), methoctramine and pirenzepine have demonstrated that the muscarinic receptor on the rat pulmonary artery endothelium which mediates vasodilation is of the M3 subtype and cannot account for the high proportion of M1 receptors identified in lung homogenates.

Animals↗

PubMedDate not supplied

Autoradiographic localization of calcitonin gene-related peptide (CGRP) binding sites in human and guinea pig lung.

125I-Human calcitonin gene-related peptide (hCGRP) binding sites were localized in human and guinea pig lungs by an autoradiographic method. Scatchard analysis of saturation experiments from slide-mounted sections of guinea pig lung displayed specific 125I-hCGRP binding sites with a dissociation constant (Kd) of 0.72 +/- 0.05 nM (mean +/- S.E.M., n = 3) and a maximal number of binding sites (Bmax) of 133.4 +/- 5.6 fmol/mg protein. In both human and guinea pig lung, autoradiography revealed that CGRP binding sites were widely distributed, with particularly dense labeling over bronchial and pulmonary blood vessels of all sizes and alveolar walls. Airway smooth muscle and epithelium of large airways was sparsely labeled but no labeling was found over submucosal glands. This localization corresponds well to the reported pattern of CGRP-like immunoreactive innervation. The findings of localization of CGRP binding sites on bronchial and pulmonary blood vessels indicate that CGRP may be important in the regulation of airway and pulmonary blood flow.

Animals↗