Specific [3H]-N-methyl scopolamine binding without cholinergic function in cultured adult skin fibroblasts

Muscarinic cholinoceptor activation modulates DNA synthesis and CD40 expression in fibroblast cells

1 The aim of the present work was to examine the role of muscarinic acetylcholine receptors (mAChR) on DNA synthesis and CD40 expression in human fibroblast cells. Neonatal human skin fibroblast cultures were stimulated with carbachol in presence or absence of specific antagonists and the following parameters were measured: identification of mAChR subtypes, DNA synthesis, inositol phosphates (InsP) production and CD40 expression. 2 Human fibroblasts express mAChR with Kd 0.47 +/- 0.11 nm and Bmax 236 +/- 22 fmol mg protein(-1). Carbachol stimulates DNA synthesis, InsP and the expression of CD40. All these effects were inhibited by atropine, mustard hydrochloride (4-DAMP) and pirenzepine but not by AF-DX 116 and tropicamide, indicating that M3 and M1 mAChR are implicated in carbachol action. The relative Ki of the antagonists obtained by competition binding assay was in parallel to the relative potency for blocking both carbachol-stimulated InsP accumulation and DNA synthesis. 3 The intracellular pathway leading to carbachol-induced biological effects involved phospholipase C and calcium/calmodulin, as U-73122 and trifluoroperazine blocked carbachol effects, respectively. Calphostin C, a protein kinase C inhibitor, had no effect, indicating that this enzyme does not participate in the system. 4 These results may contribute to a better understanding of the modulatory role of the parasympathetic muscarinic system on normal human fibroblast function.

Mast cell, myofibroblast and nerve terminal complexes in carbon tetrachloride-induced cirrhotic rat livers

BACKGROUND/AIMS

Extracellular matrices in liver fibrosis are known to be produced by myofibroblasts that are transformed from fat-storing cells. The development of the fibrotic process is thought to be mediated by various fibrogenic mediators. Recently, the involvement of mast cells and cholinergic neurotransmitters in fibrogenesis has been suggested. We have studied the distribution of these cells and cholinergic nerve fibers in normal rat livers and 6-week carbon tetrachloride-induced rat cirrhotic livers.

METHODS

Mast cells and myofibroblasts were identified by immunohistochemistry for mast cell tryptase (AA1) and alpha-smooth muscle actin. Cholinergic nerve fibers and terminals were localized using the acetylcholinesterase neurohistochemistry method for light and transmission electron microscopy.

RESULTS

In normal rat livers, a few nerve terminals were connected with fibroblasts near the vascular walls in the portal tracts. In contrast, in cirrhotic rat livers, numerous acetylcholinesterase-positive nerve fibers were observed in the fibrous septa, forming a network. Ultrastructurally, the nerve terminals were observed in close contact with mast cells and myofibroblasts in fibrous septa, forming characteristic mast cell/myofibroblast/nerve terminal complexes. In cirrhotic nodules, nerve terminals were situated in close contact with myofibroblasts in the periseptal sinusoids. These axon terminals contained numerous small clear vesicles, and acetylcholinesterase-positive products were noted in the space of the synaptic membranes.

CONCLUSIONS

Our findings demonstrate that mast cell/ myofibroblast/cholinergic nerve terminal complexes may play a role in the development of liver fibrosis, probably because of the production of extracellular matrix components by myofibroblasts.

Characterization of muscarinic acetylcholine receptors in cultured adult skin fibroblasts: effects of the Swedish Alzheimer's disease APP 670/671 mutation on binding levels

We have characterised the muscarinic receptor subtypes found in human skin fibroblasts and compared binding levels in cell lines from members of the Alzheimer's disease family with the Swedish amyloid precursor protein (APP) 670/671 mutation. Binding studies with [3H] quinuclidinyl benzilate ([3H]QNB) and the M2/M4 selective antagonist [3H] (+/-)-5,11-dihydro-11-([(2-[(di-propylamino)methyl]-1- piperidinyl]ethyl)amino]carbonyl)-6H-pyrido(2,3-b)(1,4)benzodiazepine-6- one ([3H]AF-DX 384) revealed the presence of a single population of muscarinic receptors on lysed fibroblast membranes. [3H]QNB binding was displaced by a number of selective muscarinic ligands with a rank order of potency: atropine > himbacine > methoctramine > (+/-)-p-fluoro-hexahydro-sila-difenidol hydrochloride > pirenzepine > muscarinic-toxin-3. APP 670/671 mutation carrying cell lines showed 25-35% lower levels of muscarinic receptors labelled with [3H]QNB, [3H]N-methyl scopolamine and [3H]AF-DX 384, compared to controls. This difference was not statistically significant due to large individual variation. It is concluded that muscarinic receptors on adult skin fibroblasts are predominantly of the M2 subtype. Since these cells do not possess M1 and M3 receptor subtypes, they are unlikely to provide a good model for studying muscarinic receptor regulation of APP processing.

Ultrastructure of cholinergic innervation in the cirrhotic liver in guinea pigs. Neurohistochemical and ultrastructural study

Hepatic cirrhosis was induced in guinea pigs by ligation of the common bile duct and innervation of the liver was studied by fluorescence histochemistry (glyoxylic acid method), acetylcholinesterase (AChE) neurohistochemistry (modified Karnovsky and Roots method), and transmission electron microscopy. In control animals the adrenergic terminals showed connections with endothelial cells, hepatocytes and fat-storing cells, but no cholinergic terminals were evident. Cirrhosis was present 6 weeks after the bile duct ligation and marked fibrosis, accompanied by bile duct proliferation, was evident in the portal areas. Numerous AChE-positive nerve fibers traversed the collagenous bundles in the fibrotic areas, and cholinergic terminals formed close contacts with fibroblasts. Each axon terminal was found to contain numerous small coreless vesicles and AChE-reaction products were confirmed in the space between a nerve terminal and a fibroblast. In contrast, fluorescence adrenergic nerve fibers and their terminals remained unchanged. This study demonstrates that parasympathetic cholinergic innervation participates in some stages in the development of hepatic cirrhosis.

Muscarinic cholinergic receptors on intact human lymphocytes. Properties and subclass characterization

Saturable specific binding of tritiated N-methyl-scopolamine (3H-NMS) can be demonstrated on intact circulating human lymphocytes, with an average KD of 7 nmol/liter and an average density of about 15 fmol/10(6) cells. Specific 3H-NMS binding can be inhibited by cholinergic antagonists and agonists, is highly stereospecific for the enantiomers of the cholinergic antagonist quinuclidinyl benzilate (QNB), and is modulated by the stable guanosine triphosphate (GTP) analog GppNHp in a fashion similar to the specific binding of the same radioligand to rat heart membranes. The results indicate the presence of muscarinic cholinergic receptors on intact human lymphocytes, with a predominance of the M2 subtype. As central muscarinic cholinergic receptors have been reported to play an important role in the pathogenesis of affective disorders, the lymphocyte might represent a suitable model for the study of muscarinic receptor functions in humans.