The relationship between nerves and smooth muscle cells in the rat iris

Summary The sphincter muscle in the rat iris forms irregular strands in the stroma. Bundles of unmyelinated axons run among the muscle cells. After sympathetic denervation some axons degenerate. This should indicate that sympathetic and parasympathetic nerves are present in the same nerve net. The parasympathetic axons possess varicosities, that is, enlargements containing mitochondria and synaptic vesicles. These varicosities show a similar structural relationship to the muscle cells as do the varicosities of sympathetic nerves. No obvious ultrastructural difference is observed between the sympathetic and parasympathetic varicosities.This study has been supported by research grants (U267 and Y247) from the Swedish Medical Research Council and by a Public Health Service Research Grant (NB05236-01) from the National Institute of Neurological Diseases and Blindness.     

Interactions between autonomic nerves and smooth and cardiac muscle cells in tissue culture

Specific interactions occur between nerve fibers from cultured sympathetic ganglia of guinea pigs and rats and single muscle cells from vas deferens and heart. The associations are long-lasting and resemble the pattern of autonomic neuromuscular relations in situ. In contrast, any associations formed between sympathetic nerve fibers and fibroblasts appear to be temporary. The results are discussed in relation to the normal innervation of smooth muscle and the reinnervation of explants.     

The ubiquitous localization of type I hexokinase in rat peripheral nerves, smooth muscle cells and epithelial cells

Summary An indirect immunoperoxidase technique has been used to determine the localization of type I hexokinase in a wide variety of Carnoy-fixed, paraffin-embedded rat tissues. The results suggest that the widespread tissue distribution of the isoenzyme is due to its ubiquitous localization in the nervous, smooth muscle and epithelial components of each tissue. The majority of the immunostaining was confined to cells with substantial energy requirements which are probably mainly satisfied through the breakdown of glucose. This observation is consistent with the known predominance of type I hexokinase in the central nervous system and with the regulatory role allotted to it in this tissue.     

The presence of smooth muscle cells in the rat ovary

Using a histochemical procedure for the demonstration of glycogen phosphorylase, smooth muscle cells have been demonstrated in the rat ovary around follicles, corpora lutea, atretic follicles and between groups of interstitial cells.     

The presence of smooth muscle cells in the rat ovary

Summary Using a histochemical procedure for the demonstration of glycogen phosphorylase, smooth muscle cells have been demonstrated in the rat ovary around follicles, corpora lutea, atretic follicles and between groups of interstitial cells.     

Expression of smooth muscle-specific alpha-isoactin in cultured vascular smooth muscle cells: relationship between growth and cytodifferentiation

The relationship between growth and cytodifferentiation was studied in cultured rat aortic smooth muscle cells (SMCs) using expression of the smooth muscle (SM)-specific isoactins (Vanderkerckhove, J., and K. Weber, 1979, Differentiation, 14:123-133) as a marker for differentiation in these cells. Isoactin expression was evaluated by: (a) measurements of fractional isoactin content and synthesis ([35S]methionine incorporation) by densitometric evaluation of two-dimensional isoelectric focusing sodium dodecyl sulfate gels, and (b) immunocytological examination using SM-specific isoactin antibodies. Results showed the following: (a) Loss of alpha-SM isoactin was not a prerequisite for initiation of cellular proliferation in primary cultures of rat aortic SMCs. (b) alpha-SM isoactin synthesis and content were low in subconfluent log phase growth cells but increased nearly threefold in density-arrested postconfluent cells. Conversely, beta-nonmuscle actin synthesis and content were higher in rapidly dividing subconfluent cultures than in quiescent postconfluent cultures. These changes were observed in primary and subpassaged cultures. (c) alpha-SM actin synthesis was increased by growth arrest of sparse cultures in serum-free medium (SFM; Libby, P., and K. V. O'Brien, 1983, J. Cell. Physiol., 115:217-223) but reached levels equivalent to density-arrested cells only after extended periods in SFM (i.e., greater than 5 d). (d) SFM did not further augment alpha-SM actin synthesis in postconfluent SMC cultures. (e) Serum stimulation of cells that had been growth-arrested in SFM resulted in a dramatic decrease in alpha-SM actin synthesis that preceded the onset of cellular proliferation. These findings demonstrate that cultured vascular SMCs undergo differential expression of isoactins in relation to their growth state and indicate that growth arrest promotes cytodifferentiation in these cells.     

Communication between endothelial and smooth muscle cells

Vascular endothelial cells play a fundamental role in the control of vascular tone, and therefore in the control of local blood flow, by releasing various contracting (endothelin, prostaglandins) and relaxing (prostacycline, NO) factors. An additional mechanism involving the hyperpolarization of the vascular smooth muscle cells is observed mainly in the coronary vascular bed and in the periphery. This phenomenon was attributed to an elusive endothelial factor called endothelium-derived hyperpolarizing factor (EDHF). This mechanism is now better understood. It involves first an increase in the endothelial intracellular concentration of calcium, the activation of endothelial potassium channels and the resulting hyperpolarization of the endothelial cells. The hyperpolarization of the endothelial cells is transmitted to the smooth muscle cells by different pathways. This hyperpolarization propagates along the vessels not only via the smooth muscle cells but also via the endothelial cells. Therefore, the endothelial layer can also be considered as a conducting tissue. The discovery of specific inhibitors of the endothelial cell hyperpolarization allows the assessment of the contribution of EDHF-mediated responses in the control of vascular tone.     

Interaction between nitric oxide and prostaglandin E pathways in rat smooth muscle myometrial cells

Previously, we demonstrated the presence of a nitric oxide (NO) prostaglandin (PG) pathway in myometrial cells obtained from uterine rat tissue. This pathway was modulated by estrogen and one possible function could be to modulate uterine relaxation. In the present study, we investigated the role of progesterone in the regulation of NO synthesis and the uterotonic PGE production by myometrial cells from uterine rat tissue. We worked with two groups of rats: (i) ovariectomizcd (OV) rats, without influence of sex hormones and (ii) OV rats injected with progesterone (4 mg) s.c. Myometrial uterine cells were obtained by a selective enzymatic digestion. In the incubation medium of these cells, nitrite concentration (as a measure of NO production) and PGE production were evaluated. To ensure a specific response, a competitive NOs inhibitor, N(G)-monomethyl-L-arginine; L-NMMA (300 microM) was used. We found that at 48 h of the incubation period, cells obtained from progesterone-primed uterine tissue presented an increase in the nitrite concentration concomitant with a decrease in the PGE production. When L-NMMA was added to the cells, nitrite production and PGE synthesis returned to control values. The fact that this effect had not been observed in the group of cells obtained from OV rats suggests that progesterone was responsible for it. These data provide strong evidence that in spite of the fact that estrogen and progesterone modulate the NO-PG pathway in the uterine rat tissue, the two hormones have opposite effects.     

The chronological relationship between the thickening of smooth muscle, epithelial cell proliferation and myenteric neural denervation in the rat jejunum

The jejunum of rats was treated by serosal application of a 0.2% solution of benzalkonium chloride (BAC) for 30 min. Control animals were treated with saline (0.9% NaC1). The animals were allocated to eight groups of 10 rats each and sacrificed 15, 30, 45, 60 days after BAC treatment. Segments were removed from the jejunum for neuronal counting, measurement of the smooth muscle area and morphokinetic study of the epithelium. There was a significant reduction in neuron number in the myenteric plexus 30 days after BAC treatment, thickening of smooth muscle 15-60 days after BAC treatment, but no change in epithelial cell proliferation in the jejunum at either time.     

Morphology of smooth muscle cells in the rat thoracic duct

Summary The three-dimensional cytoarchitecture and ultrastructure of the smooth muscle cells in the wall of the rat thoracic duct were investigated by scanning and transmission electron microscopy. The muscle layer basically consists of a single layer of circularly arranged cells. The smooth muscle cell is fusiform or ribbon-like in shape, as in veins or venules with a similar or smaller diameter. Connections by spinous processes are observed between adjacent muscle cells along their length. Spot-like membrane contacts frequently occur in areas where facing membranes are closely apposed. These are thought to be gap junctions and may be responsible for electrical coupling and mechanical attachment. Large invaginations arranged regularly in rows on the surface of the smooth muscle cells can be observed. These invaginations are closely associated with a flattened sarcoplasmic reticulum, and caveolae tend to open into the invaginations.     

AFDX-116 discriminates between muscarinic M2 receptors of the heart and the iris smooth muscle

Summary Studies with the atypical muscarinic antagonist pirenzepine provide convincing evidence for the classification of muscarinic acetylcholine receptors (mAChRs) into two subtypes, M₁ and M₂. The present study examines the heterogeneity of the M₂ subtype employing the newly developed competitive muscarinic antagonist, AFDX-116. Comparison of the binding affinities of pirenzepine, atropine, and AFDX-116 to mAChRs in microsomes from the rabbit cerebral cortex, heart, and iris smooth muscle shows that iris mAChRs, which are pharmacologically of the M₂ subtype, can be distinguished from M₂ cardiac receptors based on their affinity for AFDX-116. These results are consistent with the hypothesis that the M₂ receptor subtype consists of a heterogeneous population of receptors.Abbreviations mAChRs Muscarinic Acetylcholine Receptors - CCh Carbachol - NMS N-Methylscopolamine - AFDX-116 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6Hpyrido[2,3-b][1,4]benzodiazepine-6-one     

Galanin-immunoreactive nerves in the rat iris: alterations induced by denervations

Summary The iris and choroid membrane of the adult rat contain nerve fibers expressing immunoreactivity to the neuropeptide galanin. The density and distribution of galanin-positive nerve fibers varied from iris to iris and, particularly, among animals. Smooth, non-terminal axons were seen running in nerve bundles consisting of otherwise negative fibers. From the choroid membrane these bundles reached the iris via the ciliary body. Axons were frequently seen to branch giving rise to a sparse system of varicose, single fibers in the dilator plate and sphincter area. Galanin-positive fibers were sometimes also seen outlining blood vessels.Capsaicin, in a dose that causes permanent depletion of substance P- and cholecystokinin-immunoreactive fibers in the iris, caused no change in amount of galanin-positive fibers. Removal of the superior cervical ganglion caused a rapid and pronounced increase in the number of galanin-immunoreactive nerve fibers. Similarly, removal of the ciliary ganglion appeared to increase galanin immunoreactivity, while removal of the pterygopalatine ganglion was less effective. Lesioning of the trigeminal ganglion caused a disappearance of galanin immunoreactivity. The sympathetectomy-induced increase was counteracted by capsaicin.Galanin-positive nerve cell bodies were present in both the superior cervical and the trigeminal ganglia. In the superior cervical ganglion, immunoreactive galanin did not seem to coexist with neuropeptide Y-positive cells; in the trigeminal ganglion, some galanin-positive cells also contained calcitonin gene-related peptide (CGRP) immunoreactivity, while most cells did not. In the iris, double-staining suggested that CGRP and galanin immunoreactivities were contained in different fiber populations.We conclude that the rat iris and choroid membrane contain a sparse plexus of nerve fibers expressing galanin-like immunoreactivity. It is suggested that these fibers are derived from the trigeminal ganglion. The iris is able to respond with a pronounced increase in number of galanin-immunoreactive nerve fibers to certain denervation procedures.     

Development of smooth and skeletal muscle cells in the iris of the domestic duck,chick and quail

Summary Embryonic development of the avian iris muscle was studied by light and electron microscopy in order to clarify the origin of the iridial skeletal muscle cells. In normal development of the domestic duck, chick, and quail, the muscle bundles appearing in the iris at stage 35 consisted solely of smooth muscle cells. Undifferentiated cells appeared at stage 36, and finally skeletal muscle cells were observed at stage 37. This sequence suggests that stromal mesenchymal cells migrate into the muscle bundles to become skeletal muscle cells.Tissue culture of whole indes removed from duck embryos at stages 30 through 34 produced skeletal muscle cells while culture of isolated iridial epithelia removed at stages 31 and 32 did not. Removal of the midbrain region of duck embryos at stage 10 frequently produced severe disorganization of the eye concomitant with craniofacial deformities typical of a neural crest mesenchymal defect. These severely disorganized eyes were devoid of iridial skeletal muscle cells. These results also suggest mesenchymal origin of iridial skeletal muscle cells.