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PubMedDate not supplied

Physiological roles and properties of potassium channels in corporal smooth muscle.

Decreased penile vascular resistance induced by corporal smooth muscle relaxation is the most important step in penile erection. The heightened tone of the corporal smooth muscles is considered a major cause in impotence. Modulation of corporal smooth muscle tone is a complex process requiring the integration of a host of intracellular events and extracellular signals. In intracellular events of corporal smooth muscle cell, the potassium channels and calcium channels play a major role. Functionally, potassium channels are important regulators of smooth muscle membrane potential in response to depolarizing stimuli and they counteract calcium channels. Potassium channels have been shown to play a fundamental role in both the physiologic and pathophysiologic regulation of smooth muscle tone in diverse tissues. Among the several subtypes of potassium channels, the calcium-sensitive (K(Ca)) or maxi-K potassium channel subtypes are thought to be the most physiologically relevant in human corporal smooth muscle. Because of the physiological role of maxi-K channels in human corporal smooth muscles, we investigated the maxi-K channels for the genetic therapy of erectile dysfunction. These data indicate that naked hSlo DNA of maxi-K channels is quite easily incorporated into corporal smooth muscle and expression of the maxi-K hSlo cDNA appeared to be sustained for 1-4 months postinjection. These results show the possibility of a similar genetic strategy of potassium channels in humans.

Journal Article↗
PubMed1982

Tension-pCa relation and sarcoplasmic reticulum responses in chemically skinned smooth muscle fibers.

Properties of bundles of smooth muscle fibers in which the surface membrane has been rendered highly permeable by chemical treatment (saponin) are described. These preparations are termed chemically skinned smooth muscle fiber bundles. Thin bundles were isolated from guinea pig teniae ceci and skinned in a relaxing solution by treatment with 50 micrograms/ml saponin for 20-30 min. Because Ca2+ sensitivity progressively decreased on repeating contractions or on incubating in a relaxing solution, the tension-pCa (-log10 [free Ca2+]) relationship was determined soon after the skinning by a single contraction in which the [free Ca2+] was increased in a stepwise manner. Unlike skinned skeletal muscle fibers, in skinned smooth muscle fiber bundles the tension-pCa relationship was not affected appreciably by the changes in pH from 6.4 to 7.2, in ionic strength from 0.15 to 0.30 M, or in [MgATP] from 0.4 to 8 mM. The saponin-treated smooth muscle fiber bundles retained a functional sarcoplasmic reticulum (SR). Ca can be loaded in the SR if the [free Ca2+] is in the micromolar range and MgATP is present and can be released by an application of caffeine. Mitochondria also appear to be functional in saponin-treated fibers.

Adenosine Triphosphate↗
PubMed1991

Isolation of two morphologically distinct cell lines from rat arterial smooth muscle expressing high tumorigenic potentials.

Smooth muscle cell proliferation is an important feature of atherogenesis. Some works have hypothesized that a transformation of smooth muscle cells could arise during this pathological process. The present paper describes two spontaneously transformed cell lines of arterial smooth muscle cells (SMC) established from aortic media of adult rat. The cell lines have been designated V6 and V8; some of their morphologic, growth, and metabolic characteristics are described and compared to their parent cells. The two cell lines appeared distinct by their morphology and by their degree of transformation. V6 cells appeared as elongated spindle-shaped cells whereas V8 cells were spread cells with a cobblestone pattern. Karyotypes of both cell lines showed a high polyploidy level. V6 and V8 cell lines were immortalized and showed growth characteristics of transformed cells: low requirement of serum to grow, ability to form colonies in soft agar and tumorigenicity in nude mice; V8 cells presented a higher malignancy than V6 cells. Both V6 and V8 cells exhibited characteristics of cultured arterial SMC: ultrastructure, alpha actin expression at the protein and mRNA level, prostacyclin production. The remarkably different morphologies of the V6 and V8 lines and their transformed phenotype suggest that these cell lines could be useful models to study SMC differentiation and proliferation with respect to atherosclerotic or hypertensive vascular diseases.

Actins↗
PubMed1999

Biological activities of novel thienothiazine derivatives on heart and smooth muscle preparations of guinea pigs.

New thienothiazine derivatives which differ in their side chains on the nitrogen atom of the thienothiazine ring were investigated regarding their biological activity and compared with calcium antagonistic drugs. Isometric contraction force was measured in guinea-pig papillary muscles, aortic strips and terminal ilea. Chronotropic activity was studied in right atria of guinea pigs. MS 69 with a ethylpyridylcarbonyl side chain had the most potent negative inotropic effect on isolated papillary muscles, followed by MS 74, which has an ethylmethylpiperazinylthiocarbonyl side chain. The negative inotropic effect could be antagonized by increasing the extracellular calcium concentration. MS 87 with an ethylpyridylcarboxamide side chain had the most potent relaxing effect on aortic strips and MS 48 with an ethylbenzylpiperazinylcarbonyl side chain was most potent on terminal ilea. Compounds with a more hydrophilic side chain had less activity. It is concluded that increasing the lipophilicity by substitution of an oxygen atom by a sulfur atom (MS 74) or addition of a pyridine ring (MS 69) results in a higher biological activity.

Animals↗
PubMed1999

[Development of new anti-atherosclerotic drugs based on the phenotypic modulation of vascular smooth muscle cells].

We have established a novel smooth muscle cell line (SVS) which retains the expression of specific markers for smooth muscle cells, such as smooth muscle myosin-1, calponin and SM22 alpha, from temperature-sensitive SV40 large T-antigen transgenic mice. SVS cells showed temperature-dependent growth and the expression of smooth muscle markers, showing that the differentiation stage can be controlled in this cell line by culture temperature. We have constructed luciferase-reporter cell lines for calponin and SM22 alpha genes by using SVS cells. We detected some compounds including ascorbic acid, which stimulated the expression of smooth muscle markers by the reporter assay. Ascorbic acid and its long lasting derivatives stimulated the expression of markers continuously. Moreover, ascorbic acid activated the expression of markers in synthetic SMCs seen in the intima of a rat balloon injury model. Thus, this reporter system should be useful for discovery of new antiatherosclerotic drugs.

Animals↗
PubMed1993

The skeletal muscle transverse tubular Mg-ATPase: identity with Mg-ATPases of smooth muscle and brain.

Purified chicken skeletal muscle transverse tubule (T-tubule, TT) membrane preparations contain a very active Ca- or Mg-ATPase (EC 3.6.1.3) previously thought to be a T-system-specific marker enzyme. The function of the Mg-ATPase has not yet been determined although its prominent activity and concentration in junctional complexes supports a possible role in the excitation-contraction cycle. An essential component of the Mg-ATPase has been identified as a M(r) 85,000 glycoprotein (85k-GP). Polyclonal antibodies raised against the TT 85k-GP were specific and exhibited no cross-reactivity with other skeletal muscle proteins on immunoblots. Using this anti-85k-glycoprotein IgG, we have explored other chicken tissues to determine the tissue distribution of the 85k-GP. Antibody reactive polypeptides of M(r) 85,000 were found in gizzard smooth muscle, brain, heart, spleen, and lung tissue. The brain and smooth muscle membrane proteins were further purified and characterized for 85k-GP-associated Mg-ATPase activity. The brain and smooth muscle enzymes exhibited properties indistinguishable from the skeletal muscle TT-specific Mg-ATPase with regard to a series of activators and inhibitors, amino terminal amino acid sequences, and the effects of deglycosylation. The enzyme in all three tissues was inhibited by the diacylglycerol kinase inhibitor R 59022. Identification of the TT Mg-ATPase in gizzard smooth muscle has allowed the investigation of the Mg-ATPase membrane topology using isolated whole smooth muscle cells. The data support an ecto-orientation for the smooth muscle cell enzyme. Although the orientations of the brain and skeletal muscle enzymes have not been conclusively determined, the nearly identical properties of all three enzymes argues for an ecto-orientation of the active sites of these enzymes as well. The responsiveness of the three enzymes to regulatory lipids suggests that the ecto-Mg-ATPase may serve as a master switch controlling extracellular ATP concentrations and ligand accessibility to P1- and P2-purinoceptors. It is also proposed that the ecto-MgATPase may regulate ATP accessibility to ectoprotein kinases in a variety of tissues, and, in brain, the ecto-MgATPase may modulate the neurotransmitter role of ATP.

Animals↗
PubMed1991

Characterization of receptors mediating the effects of dopamine on gastric smooth muscle.

The effects of dopamine on circular and longitudinal smooth muscle from the body of the guinea pig stomach were examined. In circular muscle, dopamine (10(-6)-10(-3) mol/L) induced contractions that were tetrodotoxin-insensitive with a concentration of half-maximal effect (EC50) of 6.3 x 10(-6) mol/L for dopamine vs. 1.4 x 10(7) mol/L for norepinephrine. The efficacies of dopamine- and norepinephrine-induced contraction were similar. The alpha-adrenoceptor antagonist phentolamine competitively inhibited dopamine-induced circular contractions (Ki = 2.5 x 10(-8) mol/L slope 1.06), whereas the dopamine antagonist haloperidol had no effect. The alpha 1-antagonist prazosin competitively inhibited dopamine-induced contractions (Ki = 1.8 x 10(-8) mol/L, slope 1.03), whereas the alpha 2 antagonist yohimbine was slightly less potent (Ki = 2.2 x 10(-7) mol/L, slope 1.15). In longitudinal muscle, dopamine produced relaxation with an EC50 of 2.9 x 10(-5) mol/L vs. 2.4 x 10(-6) mol/L for norepinephrine. Tetrodotoxin reduced relaxation to dopamine by one third at low doses of dopamine (10(-5)-10(-4) mol/L) and had no effect above 10(-3) mol/L. Phentolamine did not inhibit dopamine-induced relaxation, whereas haloperidol demonstrated potent competitive inhibition (Ki = 5.8 x 10(-7) mol/L, slope 0.90). The selective DA1 antagonist Sch 23390 (Research Biochemicals Inc., Natick, MA) showed competitive antagonism (Ki = 6.3 x 10(-6) mol/L, slope 0.98), whereas the selective DA2 antagonist domperidone had no effect. The effect of Sch 23390 was tetrodotoxin resistant. It is concluded that in the body of the guinea pig stomach, dopamine induces contraction in circular muscle through smooth muscle alpha adrenoceptors, whereas in longitudinal muscle, dopamine induces relaxation through smooth muscle DA1 receptors.

Adrenergic alpha-Antagonists↗
PubMed1998

Aortic carboxypeptidase-like protein, a novel protein with discoidin and carboxypeptidase-like domains, is up-regulated during vascular smooth muscle cell differentiation.

Phenotypic modulation of vascular smooth muscle cells plays an important role in the pathogenesis of arteriosclerosis. In a screen of proteins expressed in human aortic smooth muscle cells, we identified a novel gene product designated aortic carboxypeptidase-like protein (ACLP). The approximately 4-kilobase human cDNA and its mouse homologue encode 1158 and 1128 amino acid proteins, respectively, that are 85% identical. ACLP is a nonnuclear protein that contains a signal peptide, a lysine- and proline-rich 11-amino acid repeating motif, a discoidin-like domain, and a C-terminal domain with 39% identity to carboxypeptidase E. By Western blot analysis and in situ hybridization, we detected abundant ACLP expression in the adult aorta. ACLP was expressed predominantly in the smooth muscle cells of the adult mouse aorta but not in the adventitia or in several other tissues. In cultured mouse aortic smooth muscle cells, ACLP mRNA and protein were up-regulated 2-3-fold after serum starvation. Using a recently developed neural crest cell to smooth muscle cell in vitro differentiation system, we found that ACLP mRNA and protein were not expressed in neural crest cells but were up-regulated dramatically with the differentiation of these cells. These results indicate that ACLP may play a role in differentiated vascular smooth muscle cells.

Adult↗
PubMed2000

Molecular mechanism of cGMP-mediated smooth muscle relaxation.

Contraction and relaxation of smooth muscle is a tightly regulated process involving numerous endogenous substances and their intracellular second messengers. We examine the key role of cyclic guanosine monophosphate (cGMP) in mediating smooth muscle relaxation. We briefly review the current art regarding cGMP generation and degradation, while focusing on the recent identification of the molecular mechanisms underlying cGMP-mediated smooth muscle relaxation. cGMP-induced SM relaxation is mediated mainly by cGMP-dependent protein kinase activation. It involves several molecular events culminating in a reduction in intracellular Ca(2+) concentration and a decrease in the sensitivity of the contractile system to Ca(2+). We propose that the cGMP-induced decrease in Ca(2+) sensitivity is a strategic way to achieve "active relaxation" of the smooth muscle. In summary, we present compelling evidence supporting a key role for cGMP as a mediator of smooth muscle relaxation in physiological and pharmacological settings.

Animals↗
PubMed2006

Serum response factor, its cofactors, and epithelial-mesenchymal signaling in urinary bladder smooth muscle formation.

Little is known about the mechanism of bladder smooth muscle differentiation. We hypothesize that epithelial-mesenchymal signaling induces the expression of smooth muscle proteins in bladder mesenchyme resulting in smooth muscle differentiation. We confirmed that smooth muscle differentiation in the mouse urinary bladder occurs first at gestational day 14 (E14) based upon immunohistochemical localization of smooth muscle alpha-actin (SMAA). To investigate murine bladder smooth muscle differentiation and epithlelial-mesenchymal signaling in the developing bladder, we analyzed gene expression profiles of intact embryonic murine bladders and separated epithelial and mesenchymal components at embryonic days E13, E14, E15, E16, and postnatal day 1 (P1). Using cDNA microarray, we identified regulators of vascular smooth muscle differentiation in bladder mesenchyme, including serum response factor (SRF) and its cofactors, ELK1 and SRF accessory protein (SAP)1, as well as two SRF-associated pathways, angiotension receptor II and transforming growth factor- beta2. Immunohistochemistry showed diffuse expression of SRF in the bladder at E12 with localization of expression to the peripheral mesenchyme at E13 and E14. Our results suggest that bladder smooth muscle differentiation may share a similar gene expression program as occurs during vascular smooth muscle differentiation. The unique structure of the urinary bladder makes it an ideal model for studies of smooth muscle differentiation and epithelial-mesenchymal signaling.

Animals↗
PubMed1997

Na+/K+ ATPase mediates rhythmic spontaneous relaxations in canine airway smooth muscle.

In canine airway smooth muscle, cyclopiazonic acid (CPA; selective blocker of the sarcoplasmic reticulum Ca(2+)-pump) evokes a contractile response which is initially mediated via release of internally sequestered Ca2+, but is later supported almost exclusively by electromechanical coupling. As such, this second component is highly sensitive to inhibition of voltage-dependent Ca(2+)-influx (e.g. dihydropyridines, removal of external Ca2+) or to membrane hyperpolarization. In the present study, we describe relaxations which occur spontaneously during this second component of the CPA-evoked contraction. These relaxations are also electromechanically mediated, since they are abolished by depolarization of the membrane by high-K+ media. TEA has relatively little effect on the phasic activity, thus ruling out an involvement of Ca(2+)-dependent K+ channels. On the other hand, the phasic activity is abolished by ouabain, by removal of external K+, or by cooling and is markedly slowed by removal of external Na+. These observations indicate that the phasic activity is mediated by the Na+/K(+)-ATPase.

Animals↗
PubMed1999

New benzoxazine and benzothiazine derivatives--structure-activity relations in guinea-pig heart and smooth muscle preparations.

New benzoxazine and benzothiazine derivatives which differ in their side chains on the nitrogen atom of the benzoxazine or benzothiazine ring were investigated regarding structure-activity relations and compared with calcium antagonistic drugs. The isometric contraction force was measured in guinea-pig papillary muscles, aortic strips and terminal ilea. Chronotropic activity was studied in right atria of guinea pigs. The benzoxazine derivative with a dimethoxyphenylethyl-N-methylaminoethylcarboxamide side chain (MS 84) had the most potent negative inotropic effect on papillary muscles and the most potent relaxing effect on terminal ilea. The benzothiazine derivative with a methylpiperazinylcarbonyl side chain (MS 63) was less effective. Benzoxazine derivatives with a methylpiperazinylcarbonyl (MS 64) or a N-dimethylaminoethylcarboxamide side chain (MS 66) and the benzothiazine derivative (MS 65) with an analog side chain like MS 66 only had a weak effect. We conclude that the oxygen atom in the heterocyclic ring and the lipophilic side chain on the nitrogen atom, which is almost identical with the calcium antagonistic drug KT-362 is responsible for the most potent action.

Animals↗
PubMed1994

Early changes in airway smooth muscle hyperresponsiveness.

To study asthmatic airway smooth muscle we developed a canine model of ragweed pollen sensitized, airway hyperresponsiveness because of the difficulties in obtaining human tissue. Tracheal and bronchial smooth muscles from sensitized dogs were shown to possess greater ability to shorten and higher maximum shortening velocity (Vo), both of which contribute to the excessive narrowing of airways typical of human asthma. However, maximum force production remained normal, demonstrating the dissociation between the behaviour of shortening and force. Because we found no evidence of inflammation, hypertrophy, or hyperplasia in the sensitized airway smooth muscles, we felt this is a model of early disease and should provide insight into early and perhaps primary pathogenetic mechanisms. Vo is known to be determined by actomyosin ATPase, which in smooth muscle is activated via phosphorylation of the 20-kDa myosin light chain (MLC20) by myosin light chain kinase (MLCK). Therefore, ATPase activity, MLC20 phosphorylation, and MLCK were investigated. Sensitized tracheal and bronchial smooth muscles showed significantly higher ATPase activity, and a higher level of MLC20 phosphorylation, resulting from increased MLCK activity, a consequence of the measured increase in total quantity of MLCK rather than in specific activity. Since MLCK is activated by binding with Ca(2+)-calmodulin complex, intracellular Ca2+ concentration and calmodulin activity were also assessed, but no difference was found between sensitized and control animals. Our study suggests that increased MLCK quantity may be the cause of airway hyperresponsiveness found in sensitized animals, and future investigation should be focused on depicting the reason for the elevated MLCK.

Animals↗
PubMed2004

Control of smooth muscle cell proliferation in vascular disease.

PURPOSE OF REVIEW: Smooth muscle cell proliferation has previously been regarded as a central feature in vascular disease. The role of this process has recently been substantially re-evaluated, and we have reconsidered the functional importance of smooth muscle cell proliferation, the origin of proliferating smooth muscle cells in lesions, and the mechanisms whereby smooth muscle cell proliferation is controlled. In this review, we summarize recent progress in the understanding of smooth muscle cell proliferation, with a particular focus on how interactions between the extracellular matrix, smooth muscle cells, and mitogens control critical steps in this process. RECENT FINDINGS: Irrespective of the origin of smooth muscle cells in vascular lesions, fundamental interactions between the extracellular matrix and cell surface integrins are necessary in order to initiate a proliferative response in a quiescent smooth muscle cell, in a similar manner to any non-malignant cell. These interactions trigger intracellular signaling and cell cycle entry, which facilitate cell cycle progression and proliferation by mitogens. In addition, extracellular matrix interactions may also control the availability and activity of growth factors such as heparin-binding mitogens, which can be sequestered by heparan sulfate containing extracellular matrix components and regulate smooth muscle cell proliferation. SUMMARY: New insights into mechanisms whereby the extracellular matrix takes part in the control of smooth muscle cell proliferation suggest a number of putative targets for future therapies that can be applied to increase plaque stability, prevent the clinical consequences of atherosclerosis and improve outcomes after interventional procedures and organ transplantation.

Animals↗
PubMed1987

Effect of atrial natriuretic factor on Na+-K+-Cl- cotransport of vascular smooth muscle cells.

We previously demonstrated that vascular smooth muscle cells possess a prominent Na+-K+-Cl- cotransport system that can be markedly stimulated by elevations in levels of intracellular cyclic guanosine 3',5'-monophosphate (cGMP). Since others have shown that atrial natriuretic factor (ANF) can bind to specific membrane receptors and can enhance cGMP levels in vascular smooth muscle cells, we asked whether ANF could also stimulate Na+-K+-Cl- cotransport in vascular smooth muscle cells. It was discovered that rat atriopeptin III stimulated Na+-K+-Cl- cotransport of vascular smooth muscle cells in a concentration-dependent manner. In contrast, rat atriopeptin III had no effect on two other sodium transport systems known to be present in vascular smooth muscle cells (i.e., Na+-H+ exchange and Na+-K+-adenosine triphosphatase (ATPase). These studies indicated that ANF selectively stimulates Na+-K+-Cl- cotransport of vascular smooth muscle cells. We then asked whether ANF-stimulated Na+-K+-Cl- cotransport was dependent upon the ability of ANF to enhance intracellular cGMP levels. When rat atriopeptin III-stimulated increases in cGMP were inhibited with the quinolinedione LY 83583, rat atriopeptin III could no longer stimulate Na+-K+-Cl- cotransport of vascular smooth muscle cells. Thus it appeared that the effects of ANF were dependent upon the ability of ANF to elevate intracellular cGMP levels. Finally, we asked whether ANF effects on Na+-K+-Cl- cotransport were related to the biological activity of ANF.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Cyclic AMP-mobilizing agents and glucocorticoids modulate human smooth muscle cell migration.

Hyperplasia and cell migration of smooth muscle are features of both airway and pulmonary vascular diseases. The precise cellular and molecular mechanisms that regulate smooth muscle migration in the lungs remain unknown. In this study, we examined the effect of cAMP-mobilizing agents and steroids on smooth muscle cell migration. Platelet-derived growth factor (PDGF), transforming growth factor-alpha, vascular endothelial growth factor, and basic fibroblast growth factor significantly stimulated cell migration in pulmonary vascular smooth muscle (PVSM) cells. Airway smooth muscle (ASM) migration was also stimulated by PDGF, transforming growth factor-alpha, and basic fibroblast growth factor, but vascular endothelial growth factor was without effect. Interestingly, the smooth muscle mitogen thrombin did not stimulate migration of either cell type. Agents capable of elevating intracellular cAMP inhibited basal (unstimulated) cell migration in both cell types, whereas their effects on PDGF-stimulated migration were more variable. Prostaglandin E2, salmeterol, and the phosphodiesterase type 4 inhibitor cilomolast inhibited basal ASM and PVSM migration by 30-60%. Prostaglandin E2 and cilomolast also inhibited PDGF-stimulated migration of ASM and PVSM cells, but salmeterol was without effect. Preincubation of ASM cells with dexamethasone or fluticasone inhibited basal and PDGF-stimulated migration, and enabled an inhibitory effect of salmeterol on PDGF-induced cell migration. Steroids alone did not stimulate cAMP production or cAMP/PKA-dependent gene transcription (CRE-Luc activity), but slightly augmented salmeterol-stimulated CRE-Luc activity. Collectively, these findings demonstrate that cAMP-mobilizing agents and steroids modulate human smooth muscle cell migration, likely by distinct mechanisms.

Albuterol↗
PubMed1990

Developmental changes in expression of contractile and cytoskeletal proteins in human aortic smooth muscle.

To describe phenotypic changes of human aortic smooth muscle cells (SMCs), proportion of smooth muscle and nonmuscle variants of actin, myosin heavy chains (MHCs), vinculin, and caldesmon, during prenatal and several months of postnatal development was determined. In aortic SMCs from 9-10-week-old fetus, both nonmuscle and smooth muscle-specific variants of all four proteins were present, however, the nonmuscle forms were more abundant. During development, a shift towards the expression of muscle-specific variants was observed, although the time course of changes in protein variant content was not similar for all the proteins studied. By the 24th week of gestation, fractional content of alpha-smooth muscle actin and smooth muscle MHCs was rather close to that in the mature SMCs, and comprised approximately 80 and 90%, respectively, of the levels characteristic of SMCs from adult aortic media. On the contrary, fractional ratio of meta-vinculin and 150-kDa caldesmon was still rather low in the aorta from the 24-week-old fetus, did not increase in a 2-month-old child aorta, and did not reach the level characteristic of mature SMCs even in the 6-month-old child aorta. Thus changes in alpha-smooth muscle actin and smooth muscle MHC fractional content occur mainly during the prenatal period of development, before the 24th week of gestation; while meta-vinculin and the 150-kDa caldesmon proportion increases mainly in the postnatal period, during several months after birth. In the "Discussion," phenotypes of SMCs from developing aorta were compared to those from different layers of the adult aortic wall.

Actins↗
PubMed1990

Derivation and properties of platelet-derived growth factor-independent rat smooth muscle cells.

The present study reports that smooth muscle cells can be derived from the adult rat aorta without being exposed to serum containing platelet releasate, these cells can also be grown and passaged in medium lacking detectable quantities of platelet-derived growth factor (PDGF). As reported earlier, smooth muscle cells grown from the newborn or injured vessels have a distinctive epithelioid appearance. The platelet factor independent smooth muscle cells have a similar appearance. Unlike the cells from newborn animals or from injured vessels, smooth muscle cells derived in this way from the adult animal do not produce PDGF, although they do display PDGF receptors. Studies in serum-free medium show that the PDGF-independent cells can respond to PDGF when all other components of serum are absent; however, growth of these smooth muscle cells proceeds equally well in low concentrations of serum, independent of the presence of PDGF or other growth factors detectable by growth-promoting assays using either 3T3 cells or smooth muscle cells whose growth is dependent on factors present in whole blood serum. Taken together with recent observations in vivo, these data suggest that growth of at least some smooth muscle cells may depend on mechanisms independent of release of growth factors by platelets.

Animals↗