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PubMed1975

Trophic influences of sympathetic nerves and cyclic AMP on differentiation and proliferation of isolated smooth muscle cells in culture.

Smooth muscle cells of the newborn guinea-pig vas deferens dispersed into single cells and grown in culture maintain their differentiation for approximately 5 days before undergoing dedifferentiation and mitosis. The presence of sympathetic nerve fibres in contact with the isolated cells delays this process by 3-7 days (Chamley et al., 1974). A similar delay in dedifferentiation of vas deferens smooth muscle cells in tissue culture in the presence of sympathetic ganglion extract is described in the present report, demonstrating that the trophic effect is elicited by a chemical substance. This effect is mimicked by the presence of either a confluent layer of RKA epithelial cells, dibutyryl cyclic AMP or theophylline. A similar, but considerably weaker, effect is also obtained with spinal cord and liver extracts and noradrenaline. Acetylcholine does not show an effect. It is suggested that a trophic substance (probably not noradrenaline) from sympathetic neurons activates the adenyl cyclase system of smooth muscle cells to increase the intracellular level of cyclic AMP which in turn promotes and maintains the differentiation of the cultured smooth muscle cells.

Acetylcholine↗
PubMed1979

Interaction of acetylcholine and cholecystokinin with dispersed smooth muscle cells.

Isolated gastric smooth muscle cells were prepared from the stomach of Bufo marinus by successive incubation in collagenase without added trypsin. Contraction was determined by image-splitting micrometry and expressed as the mean percentage decrease in cell length from control. Peak contractile response was attained within 30 s. Dose-response curves constructed from peak responses showed that the maximal responses to CCK-OP (37.2 +/- 3.8%), acetylcholine (35.3 +/- 2.5%), and Ca2+ (42.3 +/- 0.9%) were similar. The D50s for octapeptide of cholecystokinin (CCK-OP) and acetylcholine were around 10(-12) M and 10(-11) M, respectively. The response to a combination of submaximal concentrations of acetylcholine and CCK-OP exceeded the individual responses but did not exceed the maximal response to either agent alone. A low concentration of atropine (5 X 10(-10) M) inhibited specifically the maximal response to acetylcholine. A high concentration of atropine (5 X 10(-8) M) inhibited partially the maximal response to CCK-OP but had no effect on the maximal response to Ca2+. It was concluded that 1) dispersed gastric smooth muscle cells are highly sensitive to stimulation; 2) CCK-OP has a direct (myogenic) contractile effect on gastric smooth muscle; and 3) the effect of CCK-OP and acetylcholine are mediated by separate receptors.

Acetylcholine↗
PubMed1975

Synthesis of type I collagen by human smooth muscle cells in vitro.

Human vascular smooth muscle cells, derived from explants of medial smooth muscle of a fetal aorta, were grown in vitro and examined with phase and electron microscopy for characteristic morphologic features of smooth muscle cells and for the biosynthesis of connective tissue proteins. Their patterns of growth and ultrastructure were similar to those described for other species of cultured arterial smooth muscle cells. Most cells contained varying amounts of myofilaments interpersed with dense bodies, rough and smooth endoplasmic reticulum, mitochondria, various sized vesicles, lysosomes, and lipid droplets. Extracellularly, small amounts of electron-dense material and microfilaments were observed adjacent to or between the cells. The over-all morphology suggested that the smooth muscle cells were actively engaged in protein synthesis. Although we could not identify banded collagen fibrils in 10- to 14-day-old cultures by electron microscopy, the cells synthesized and secreted a collagen characterized as type I collagen. A hydroxyproline-containing protein composed of two alpha-1 and one alpha-2 chains was extracted from the cell layer. The triple helical precursor of type I collagen, procollagen, was secreted into the medium.

Aorta↗
PubMed1979

Temperature- and Mg-ATP-dependent regulation of Ca2+ sensitivity of smooth muscle actomyosin ATPase.

Many smooth muscles on metabolic depletion undergo a contraction that is insensitive to EGTA [ethylene glycol-bis (beta-aminoethylether)N,N-tetraacetic acid]. Chicken gizzard actomyosin shows a progressive loss of Ca sensitivity accompanied by activation of EGTA-Mg-ATPase at temperatures near 37 degrees C with decreasing ATP concentrations. Ca2+-dependent phosphorylation still occurs under these conditions when the ATPase is Ca insensitive. Activation of EGTA-Mg-ATPase at low ATP concentration is not due to a pseudo-ATPase, or due to denautration of the actomyosin at 37 degrees C. Magnesium concentrations above 1 mM are required for observing the enhanced EGTA-Mg-ATPase activity and the Ca sensitivity is very markedly influenced by the magnesium concentrations of medium at low ATP. When the Mg-to-ATP ratio (5:1) was kept constant for varying ATP concentrations, activation of EGTA-ATPase was not observed. This activation was not due to the characteristics of the ATP regenerating system (phosphoenolpyruvate and pyruvate kinase) because with phosphocreatine and creatine phosphokinase similar results were obtained. Thus the EGTA-insensitive rise in tension during metabolic depletion is due to activation of Mg-ATPase and loss of Ca sensitivity at 37 degrees C, a temperature at which mammalian smooth muscles normally function.

Actomyosin↗
PubMed1976

Lipoprotein uptake and degradation by cultured human arterial smooth muscle cells.

The multipotential smooth muscle cell (SMC) is the predominant cell in intima and media of large arteries, proliferating eraly in the development of atheroma to become the lipid-laden foam cell. Thomogeneous cultures of human SMA have now been successfully grown from explants of normal pieces of artery obtained during surgery. In contrast to previous results with rat SMC, human SMC preferentially bind and take up large, lipid-rich lipoproteins (I125 labeled low density and very low denstiy lipoproteins) (LDL and VLDL), in comparison to smaller, high density lipoproteins (HDL). This species selectivity appears to be related to differences both in cells and in lipoproteins. Specific binding of lipoproteins by SMC, analyzed by release of radioactive protein from the cell surfaces by trypsin, accounted for approximately hal of the protein radioactivity associated with the cell layer during the first few hours of incubation. Specific binding appears to be related to the presence of apoprotein B on the lipoproteins. Lipoproteins progressively accumulate within cells as a function of incubation time. Lipoprotein degradation, assessed by appearance of TCA soluble, non-iodide radioactivity in the incubation medium, increased rapidly after an initial delay of 2 to 4 hours. Cells grown under hypoxic (5% O2) conditions instead of the usual room air showed impaired degradation of lipoproteins. These results suggest that there are receptors on arterial SMC, highly specific for different lipoproteins (as shown for skin fibroblasts). This tissue culture system may be useful for assessment of the effects of a variety of hormones, metabolites, and drugs on the handling of lipoproteins by arterial smooth muscle cells.

Arteries↗
PubMed1979

Migration of human vascular endothelial and smooth muscle cells.

Migration of endothelial and smooth muscle cells was studied in vitro by measuring the increase in surface area at specific time intervals of confluent cell colonies advancing under agarose gels that contained both Morgan's medium 199 and variuos types of sera. First passage cultures of endothelial cells or 3 to 6 passage smooth muscle cells were plated into wells punched in agarose gels, at a seeding density of 50,000 cells per well. At zero time the size of the cell colonies was 35.4 sq. mm. +/- standard error 0.1. Irradiation (1500 rads) did not affect the expansion of the cell colonies although 3H-thymidine uptake was inhibited. Endothelial cells migrated under the agarose gels concentrically as contiguous sheets. When exposed to either 20 per cent platelet-poor plasma serum, platelet-rich plasma serum, or whole blood serum, the average increase in surface area was approximately 9 sq. mm. per day. In contrast, arterial smooth muscle cell colonies expanded with an increment of approximately 9 sq. mm. per day when exposed to 10 per cent platelet-poor plasma serum but 12 sq. mm. per day when exposed to 10 per cent platelet-rich plasma serum (p less than 0.001). Platelet factors also had stimulatory effects on the migration of venous smooth muscle cells. Cytochalasin B, dibutyryl cyclic AMP, and theophylline inhibited the migration of both endothelial and smooth muscle cells, but the latter responded more to the inhibitory effects of all three agents. It is concluded that in contrast to vascular smooth muscle, endothelial cells do not require platelet factors for migration and are less responsive to specific inhibitors affecting cell movement.

Blood Platelets↗
PubMed1977

Studies on isolated smooth muscle cells: The contractile apparatus.

Smooth muscle cells may be isolated from the taenia coli muscle of the guinea pig which, when made permeable by treatment with Triton X-100 (0-05%) show a sensitivity to Ca for contraction with MgATP. The rate of contraction, about 10 micron s-1, corresponds closely to the maximum velocity of shortening of the intact muscle. Electron microscopy of such partially demembranated muscle cells shows that myosin filaments of about 16-nm diameter are present in both the rigor and the relaxes states. In addition, the actin and myosin filaments are commonly seen to be associated in groups corresponding approximately in size to the fibrils recognizable in cells in rigor in the light microscope. The dense bodies and the 10-nm filaments are found located between the actin-myosin filament groups. The thick myosin filaments may be isolated by fragmentation of the cells under relaxing conditions. These native filaments range up to about 8 micron in length and show the same structural organization as filaments aseembled from purified smooth muscle myosin: there is no central bare zone and bare edges, about 0-2 micrin long, occur at the filament ends. The lack of bipolarity of the native smooth muscle muosin filaments and the absence, in the contractile apparatus, of actin-associated structures equivalent to Z-lines suggests that the amount of shearing that can occur between the actin and myosin filaments is considerably greater than in skeletal muscle.

Animals↗
PubMed1978

The effect of lysolecithin on contractile force of isolated gastric smooth muscle.

Mechanical activity of smooth muscle preparations was recorded in circular strips of antrum, corpus, and fundus from guinea-pig stomach. Whereas acetylcholine stimulated both rhythmic and tonic (shift of the base line) activity of the tested muscles, lysolecithin induced tonic contractions, but had no influence on the rhythmic activity. Lysolecithin was ineffective in the absence of external calcium. The tonic activations of corpus and fundus preparations induced by lysolecithin were suppressed by sodium nitroprusside. D 600 (methoxy-verapamil) did not counteract the lysolecithin effect.

Animals↗
PubMed1977

p-Chlorophenoxyisobutyrate enhanced retention of homologous lipoproteins by human aortic smooth muscle cells.

Human aortic smooth muscle cells (SMC) specifically bind and take up indiscriminately both the lipid and protein moieties of homologous 25I-very low density lipoproteins (VLDL) and 125I-low density lipoproteins LDL). Sixty-five to 80% of absorbed lipids are incorporated into the cell lipids, preferentially into the phospholipid fraction. Twenty to 35% of the lipid bound and the protein moiety are eliminated from the cells. Half of the eliminated protein label is recovered as TCA soluble products. Five mM of p-chlorophenoxyisobutyrate (CPIB) raise the level of intracellular radioactivity derived from the lipid moieties of VLDL and LDL by about 40% via a reduced elimination. The processing of the protein moiety and lipoprotein binding to the cell surface are not affected by 5.0 mM of CPIB. CPIB lowers the incorporation of 14C-acetate, 14C-pyruvate, and 32phosphate radioactivity into fatty acids and phospholipids of aortic SMC. Five mM of CPIB reduce the overall palmitic acid synthesis by shifting from de novo synthesis to the mechanism of chain elongation, although the further elongation to saturated C18-C24 fatty acids is also depressed. The CPIB-enhanced retention of the lipid-derived lipoprotein radio-activity is interpreted as a compensatory mechanism providing cellular fatty acids which are deficient as a result of the CPIB inhibited synthetic processes.

Aorta, Thoracic↗
PubMed1978

Studies on the properties of triphosphoinositide phosphomonoesterase and phosphodiesterase of rabbit iris smooth muscle.

The rabbit iris smooth muscle has been shown to contain triphosphoinositide phosphomonoesterase (phosphatidyl-myo-inositol-4,5-bisphosphate phosphohydrolase, EC 3.1.3.36) and phosphodiesterase (triphosphoinositide inositoltrisphosphohydrolase, EC 3.1.4.11) activities. Under our experimental conditions about 77% of the phosphomonoesterase and 61% of the phosphodiesterase activities were localized in the particulate fraction. The kinetic properties of the enzymes in the microsomal fraction were examined. The enzyme preparation was specific to polyphosphoinositides; it did not attack phosphatidylinositol under the present assay condition. The effects of Ca2+ and Mg2+ were also studied. Although the microsomal enzymes did not require added divalent cations for their activities, both the phosphomonoesterase and phosphodiesterase were appreciably inhibited by 1 mM EDTA. Phosphodiesterase and phosphomonoesterase were stimulated by Ca2+ and Mg2+, respectively. The demonstration of triphosphoinositide phosphodiesterase in the iris muscle, coupled with the findings that this enzyme is activated by Ca2+ and is not influenced by acetylcholine add further support to our previous conclusion (J. Pharmacol. Exp. Ther. (1978) 204, 655--668; J. Neurochem. (1978) 30, 517--525) that an increased Ca2+ influx, following the interaction between the neurotransmitter and its receptor, could act to stimulate the phosphodiesterase, thus leading to increased triphosphoinositide breakdown and increased phosphatidic acid via increased diacylglycerol.

Animals↗
PubMed1977

Mechanism of isoproterenol-induced desensitization of tracheal smooth muscle.

Isolated rat tracheal smooth muscle became considerably less sensitive to the relaxing action of isoproterenol after being incubated with 5 x 10(-6) M isoproterenol for 30 minutes. Pretreatment of the tissue with propranolol, but not with methylprednisolone, clearly reduced the isoproterenol-induced desensitization. This suggested that propranolol by occupying the beta adrenergic receptor prevented isoproterenol from binding to this receptor, thereby preventing the isoproterenol-induced desensitization. Furthermore, an isoproterenol-desensitized tracheal preparation exhibited a diminished sensitivity to other beta agonists, but not to the spasmolytic actions of D600, hydralazine, sodium nitrite and aminophylline. These results suggested that the beta receptor is specifically involved in the desensitization induced by isoproterenol. A highly desensitized tissue could always be made to undergo complete relaxation by exposing it to sufficiently high concentrations of isoproterenol. Thus, there appeared to be no positive indication of a very large change in the apparent intrinsic activity of the isoproterenol in the desensitized tissue. However, the dissociation constant for the propranolol-beta receptor complex in the desensitized tissue was shown to be 180-fold larger than that in the normal tissue. These findings provide strong evidence that one demonstrable cellular change that occurs in the desensitized tissue is a pronounced reduction in the affinity of the beta receptors for isoproterenol.

Adrenergic beta-Agonists↗
PubMed1977

Ca2+ regulation in vascular smooth muscle.

Regulation of aorta smooth muscle contraction by Ca ion requires the collaboration of the 80,000 dalton factor and tropomyosin. A method for preparing pure actin from aorta smooth muscle is described.

Actins↗
PubMed1977

Studies on the function and composition of the 10-NM(100-A) filaments of vertebrate smooth muscle.

The extraction of isolated vertebrate smooth muscle cells at high and low ionic strength yields cell ghosts which are seen in the electron microscope to be composed of a complex network of 10-nm filaments, together with residual actin. After SDS-gel electrophoresis of the cell ghosts only 2 bands may be recognized, one corresponding to actin and the other migrating at about 55 000 mol. wt that arises from the 10-nm filaments. The 10-nm filaments are extremely sensitive to proteolysis and are absent from cells exposed to crude collagenase in the presence of Triton X-100. Such cells, lacking 10-nm filaments, still contract in response to ATP. The data indicate that the 10-nm filaments are not essential for contraction, but rather form a specialized intracellular cytoskeleton. While completely insoluble in concentrated salt solutions the 55 000 mol. wt protein is readily extracted with acetic acid from homogenized and salt-extracted smooth muscle residue. The extracted protein reassembles, on dialysis, into filaments of about 10-nm diameter and has an amino acid composition almost identical to that deduced for vertebrate neurofilaments. From the cytoskeletal role that the 10-nm filaments play in smooth muscle and, as appears likely, in other cell types the filament protein has been tentatively termed 'skeletin'. Results relating to the proportion of skeletin in smooth muscle and the structure of the 10-nm filaments are described and discussed.

Amino Acids↗