Isolation and characterization of guinea-pig tracheal smooth muscle cells that retain differentiated function in long-term subculture

Modulation of smooth muscle phenotype in vitro by homologous cell substrate

We have developed a novel cell culture system that supports the shortening of smooth muscle cells. Primary rat airway smooth muscle cells were plated on an ethanol-fixed, confluent monolayer of homologous smooth muscle cells (homologous cell substrate, HCS). Cells grown on HCS exhibited morphological and functional characteristics consistent with a differentiated phenotype. Cells on HCS were spindle shaped with a well-defined long axis, whereas cells grown on glass were larger and irregularly shaped. Smooth muscle-specific alpha-actin immunostained diffusely in cells on HCS, whereas it appeared as stress fibers in cells on glass. Agonists recruited a greater fraction of HCS cells to contract, resulting in greater changes in cell area or length on average, but the maximal capacity of shortening of individual cells was similar between the groups. Unlike cells on glass, cells on HCS shortened to methacholine. HCS was reversible and persisted over several passages. Agonists stimulated intracellular Ca(2+) oscillations in cells on HCS, whereas they elicited biphasic peak and plateau transients in cells on glass. HCS modulates smooth muscle cell phenotype in vitro.

Calcium and growth responses of hyperresponsive airway smooth muscle to different isoforms of platelet-derived growth factor (PDGF)

Airway smooth muscle (ASM) mass is likely to be an important determinant of airway responsiveness. Highly inbred Fisher rats model innate hyperresponsiveness, and also have more ASM in vivo than control Lewis rats. Platelet derived growth factor (PDGF) is an important endogenous growth factor for ASM, and partially purified PDGF-AB causes enhanced growth of Fisher rat ASM cells, compared to Lewis cells. The aim of the present study was to determine the mitogenic effects of all three recombinant PDGF isoforms on ASM cells, and investigate the mechanisms of enhanced Fisher ASM growth responses. The potential mechanisms assessed include PDGF receptor expression and activation (tyrosine phoshorylation), and intracellular calcium (Ca2+) responses to PDGF isoforms. Fisher ASM cells had a greater mitogenic response to PDGF-AB and -AA, and a greater Ca2+ response to -BB than Lewis ASM cells. A Ca2+ response was not necessary for a mitogenic response, and the effects of PDGF isoforms on Ca2+ were not associated with their effects on growth. Therefore, we suggest that enhanced Fisher mitogenic response to PDGF-AA and -AB is not mediated by differences in Ca2+ signalling. Western analysis of the PDGF receptor indicated a similar expression of β-PDGF receptor in ASM cells from the two rat strains, but a greater expression of α-PDGF receptor in Fisher cells; however, phosphorylation of the PDGF receptor following growth stimulation did not differ between strains. This suggests a role for post-receptor signals, in addition to enhanced receptor expression, in the enhanced growth response of Fisher ASM cells to PDGF-AA and -AB.Key words: PDGF receptors, tyrosine phosphorylation, intracellular calcium, proliferation, airway smooth muscle cells.

Protein kinase C is involved in enhanced airway smooth muscle cell growth in hyperresponsive rats

Fischer rat airway smooth muscle (ASM) models two potential risk factors for asthma: hyperresponsiveness to contractile agonists and to growth stimuli. The aim of this study was to identify the mechanisms responsible for enhanced ASM mitogenic response in Fischer rats compared with the control Lewis strain. The enhanced Fischer ASM cell growth response to fetal bovine serum (FBS) could not be accounted for by phospholipase C, mitogen-activated protein kinases, or tyrosine kinase activities as assessed by pharmacological inhibition and Western blotting. In contrast, depletion of phorbol ester-sensitive isoforms of the serine/threonine kinase protein kinase C (PKC) removed the difference in growth response between the rat strains. Additionally, FBS selectively induced serine/threonine phosphorylation of a 115-kDa protein in Fischer ASM cells. Enhanced activation of PKC-betaI and decreased activation of PKC-delta in Fischer compared with Lewis cells following FBS stimulation were suggested by Western blotting of membrane and cytosolic fractions. The data are consistent with a role for PKC in the enhanced ASM cell growth of hyperresponsive rats.

Nitric oxide synthesis by tracheal smooth muscle cells by a nitric oxide synthase-independent pathway

Nitric oxide (NO) is known to be synthesized from L-arginine in a reaction catalyzed by NO synthase. Liver cytochrome P-450 enzymes also catalyze the oxidative cleavage of C==N bonds of compounds containing a -C(NH2)==NOH function, producing NO in vitro. The present study was designed to investigate whether there was evidence of a similar pathway for the production of NO in tracheal smooth muscle cells. Formamidoxime (10(-2) to 10(-4) M), a compound containing -C(NH2)==NOH, relaxed carbachol-contracted tracheal rings and increased intracellular cGMP in cultured tracheal smooth muscle cells, whereas L-arginine had no such effect. NO was detectable in the medium containing cultured tracheal smooth muscle cells when incubated with formamidoxime. Ethoxyresorufin (10(-7) to 10(-4) M), an alternate cytochrome P-450 substrate, inhibited formamidoxime-induced cGMP accumulation as well as tracheal ring relaxation in cultured tracheal smooth muscle cells. The NO synthase inhibitors Nomega-nitro-L-arginine (10(-3) M) and NG-monomethyl-L-arginine (10(-3) M) had no effect on formamidoxime-induced cGMP accumulation. These results suggest that NO can be synthesized from formamidoxime in tracheal smooth muscle cells, presumably by a reaction catalyzed by cytochrome P-450.

Effects of purinoceptor agonists on cytosolic Ca2+ concentration in swine tracheal smooth muscle cells in culture

1. The effects of various purinoceptor agonists on intracellular Ca2+ concentration ([Ca2+]i) in swine tracheal smooth muscle cells in primary culture were examined to investigate the subtype of purinoceptors in these cells. 2. ATP (1 microM to 1 mM) concentration-dependently increased [Ca2+]i which was measured by monitoring the fluorescence signal of fura2. 3. alpha, beta-Me ATP at concentrations higher than 10 microM increased [ca2+]i in the presence of extracellular Ca2+. Responses to the drug were 12 +/- 5 and 61 +/- 4% of responses to ATP (100 microM) at 100 microM and 1 mM, respectively (n = 7). The response to 100 microM ATP was inhibited by 62% in the presence of 1 mM alpha, beta-Me ATP (n = 8), though the drug at concentrations lower than that did not affect the response to ATP. 4. ATP increased [Ca2+]i in the absence of extracellular Ca2+. The response to ATP in this condition was 40% of that in the presence of extracellular Ca2+ (n = 8). 5. Neither cibacron blue 3GA (10 microM) (n = 8) nor suramin (10 and 100 microM) (n = 10) affected the response to ATP (1 microM to 100 microM). 6. The rank order of potency in the absence of extracellular Ca2+ was UTP > ATP > adenosine 5'-o-(3-thiotriphosphate) > > ADP = alpha, beta-methylene adenosine 5'-triphosphate > 2-(methylthio)-adenosine 5'-(tetrahydrogen triphosphate). 7. UTP (1 microM to 100 microM) concentration-dependently increased inositol 1,4,5-triphosphate (IP3) production. 8. These results suggest that the increase in [Ca2+]i induced by purinoceptor agonists is mediated mainly via a nucleotide receptor in swine tracheal smooth muscle cells in primary culture.

Primary culture of canine tracheal smooth muscle cells in serum-free medium: effects of insulin-like growth factor I and insulin

The effects of growth factors on cell growth and muscarinic receptor (mAChR) expression of canine tracheal smooth muscle cells (TSMCs) were observed under serum-free medium supplemented with 0.1% BSA. In the presence of 0.1% BSA, TSMCs withdraw from cell cycle as compared with 10% FBS and allow to determine the effects of growth factors on mAChR expression. The individual components of growth factors (IGF-I, insulin, and aFGF) at the concentration used are not sufficient to stimulate growth of TSMCs in the primary culture with 0.1% BSA. IGF-I (10 ng/ml) and insulin (1 microgram/ml), alone or in combination, could stimulate the expression of mAChRs of cultured TSMCs. Heparin could inhibit these stimulatory effects of mAChR expression. The stimulatory effects of IGF-I and insulin on mAChR expression were mediated through their own receptors since these effects were reversed by pretreatment of TSMCs with antibodies of the respective growth factor receptors. The pharmacological response of functional mAChRs, determined as accumulation of inositol phosphates induced by carbachol, is greater in the medium containing IGF-I and insulin than that cultured in 0.1% BSA. These results firmly establish that IGF-I and insulin could stimulate the expression of mAChRs in TSMCs under serum-free culture condition.

Maintenance of contractility in dissociated smooth muscle: low-density cultures in a defined medium

The loss of contractility in long-term cultures of dissociated smooth muscle is such an established observation that the lack of contractility of cultured smooth muscle cells is often not even noted. This report describes methods of dissociating and culturing smooth muscle cells from the avian amnion that maintain contractility for > 1 mo in a defined medium. Because contractility was assessed by monitoring the contractions of individual cells to neurotransmitter-related substances, it is clear that these cells maintained both contractility and pharmacological responsiveness. However, when amniotic smooth muscle cells were dissociated with enzymes containing impurities or cultured in the presence of serum, they flattened and lost contractility, as reported for many other types of smooth muscle.

Increased contraction and inositol phosphate formation of tracheal smooth muscle from hyperresponsive guinea pigs

Tracheal smooth muscle from guinea pigs with documented airway hyperresponsiveness in vivo after multiple antigen challenges produced 30% to 50% greater force than tracheas from control guinea pigs, when stimulated with carbachol, histamine, or leukotriene D4. When cultured smooth muscle cells were incubated with myo[2-3H]inositol, basal uptake of [3H]inositol was similar in cells from normal and hyperresponsive guinea pigs, but when these cells were stimulated with contractile agonists, there was increased uptake of inositol in hyperresponsive cells. Analysis of inositol phosphates by column chromatography and high-performance liquid chromatography revealed the presence of inositol-1,4,5-triphosphate, inositol-1,3,4-trisphosphate, inositol-1,4-bisphosphate, and inositol-1-monophosphate. The release of inositol-1,4,5-triphosphate, inositol-1,4-biphosphate, and inositol-1-monophosphate by smooth muscle cells stimulated with carbachol, leukotriene D4, or histamine was 20% to 40% greater in cells derived from hyperresponsive animals than cells from normal animals. These data demonstrate that the increased muscle contraction of hyperresponsive guinea pig tracheas is associated with increased inositol phosphate metabolism in these cells. Delineating the mechanisms of airway smooth muscle contraction should provide new pharmacologic targets for the inhibition of bronchoconstriction in asthma.

Identification of adenylate cyclase-coupled histamine H2 receptors in guinea pig tracheal smooth muscle cells in culture and the effect of dexamethasone

Histamine acts on airway contractile elements through at least two different receptor subtypes: H1, which mediates Ca(2+)-dependent contraction, and H2, which stimulates cyclic adenosine monophosphate (cAMP) synthesis and possibly relaxation. The aim of this study was to determine the relative contribution of the different receptor subtypes to histamine-stimulated cAMP production by guinea pig tracheal smooth muscle (GPTSM) cells in primary culture. Histamine and N-alpha-methylhistamine induced concentration-dependent cAMP synthesis; these effects were entirely blocked by 10(-4) M cimetidine, an H2-receptor antagonist, whereas 10(-6) M thioperamide, a selective H3 blocker, was ineffective. The H3 agonist, R-(alpha)-methylhistamine, did not stimulate cAMP synthesis. Triprolidine, an H1 antagonist, did not modify histamine (10(-5) M)-stimulated cAMP synthesis. Histamine (10(-5) M) doubled [Ca2+]i in GPTSM. A 24-h pretreatment of GPTSM cells with 10(-6) M dexamethasone enhanced cAMP synthesized in response to 10(-5) M histamine and to 5 x 10(-6) M forskolin but did not significantly alter either the affinity or the binding capacity for [3H]-tiotidine, an H2-receptor antagonist. These results indicate that GPTSM cells in culture express H2 but not H3 receptors, which are linked to adenylate cyclase; their functional expression does not seem to be modulated by the concurrent activation of H1 receptors, whose presence in GPTSM is evidenced by a histamine-stimulated increase in [Ca2+]i. The most likely site of action of dexamethasone in enhancing histamine-stimulated cAMP synthesis is at the level of adenylate cyclase since the steroid had no effect on the H2 receptor itself.

Characterization of thromboxane A2/prostaglandin H2 receptors and histamine H1 receptors in cultured guinea-pig tracheal smooth-muscle cells

We characterized thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors and histamine H1 receptors in Guinea-pig cultured tracheal smooth-muscle cells (TSMC). [3H]SQ 29,548 (a TXA2 antagonist)-binding sites were saturable and a high affinity with a dissociation constant of 6.2 +/- 0.60 nM (mean +/- S.E.) and a receptor density of 46 +/- 4.6 fmol/10(6) cells. [3H]SQ 29548 binding was completely inhibited by TXA2 mimetics or antagonists. Intracellular calcium concentration ([Ca2+]i) in TSMC was increased with U46619 stimulation and the increase was attenuated by TXA2 antagonists, the potencies of which correlated with those inhibiting the activities of the [3H]SQ 29548 binding. [3H]Mepyramine (a H1 antagonist)-binding sites were also present in TSMC. [3H]Mepyramine had a single class of low-affinity-binding sites with a dissociation constant of 2.6 +/- 0.081 microM and a receptor density of 10.6 +/- 0.11 nmol/mg protein. [3H]Mepyramine binding in TSMC membrane was inhibited by H1 antagonists, but not by H2 antagonists. The inhibition constants of mepyramine in TSMC were 910-times lower than those in tracheal membranes. In contrast, the histamine-induced increase in [Ca2+]i in TSMC was inhibited in the presence of low concentrations of H1 antagonists. All these observations provide evidence that TXA2/PGH2 receptors, mepyramine-binding sites and/or H1 receptors are expressed in cultured TSMC.

Polyphosphoinositide hydrolysis and protein kinase C activation in guinea pig tracheal smooth muscle cells in culture by leukotriene D4 involve a pertussis toxin sensitive G-protein

Leukotriene D4 (LTD4) at concentrations greater than 1 nM induced phosphatidylinositol bisphosphate (PIP2) hydrolysis and protein kinase C (PKC) activation in primary culture of airway smooth muscle cells. Within seconds of activation, an increase in inositol 1,4,5-trisphosphate (IP3) was observed reaching a maximum at 5 min. The level of IP3 decreased after 5 min and was followed by an increase in inositol 1,4-bisphosphate (IP2) and inositol 1-monophosphate (IP1). LTD4-induced PIP2 hydrolysis was inhibited by 1 h pretreatment of cells with 10 micrograms/ml of pertussis toxin (PTX). LTD4 activated both soluble and particulate forms of PKC by 2-3-fold. The LTD4-induced PKC activation was blocked by treatment of cells with PTX, suggesting the involvement of a PTX-sensitive G-protein. To assess the involvement of G(i) in smooth muscle cell receptor activation, the modulation of adenylyl cyclase activity was investigated. LTD4 did not stimulate cAMP formation in smooth muscle cells, and did not inhibit forskolin-induced cAMP formation. These data suggest that the LTD4 receptor in airway smooth muscle cells is coupled to a PTX-sensitive G-protein, possibly G(o).

Heat-labile toxin from Bordetella parapertussis induces contraction of smooth muscle cells in culture

The ability of Bordetella heat-labile toxin (HLT) to contract various types of cells in culture was examined. HLT from B. parapertussis induced contraction of cultured smooth muscle cells from trachea, intestine, uterus and vas deferens as well as from aorta. The time required for contraction decreased as the dose of B. parapertussis HLT increased from 3 to 100 MID/ml. Upon exposure of cells to concentrations of toxin greater than 100 MID/ml, at least 2 hr was required for contraction. HLT from B. parapertussis did not affect cultured cardiac or skeletal muscle cells within 8 hr after the exposure to HLT (100 MID/ml). No effect on other types of primary culture cells or established cells such as Chinese hamster ovary (CHO) cells has been described. These data indicate that the primary target cells for HLT might be smooth muscle cells.

Regulation of functional muscarinic receptor expression in tracheal smooth muscle cells

Recent studies have shown that cultured tracheal smooth muscle cells (TSMCs) do not respond to muscarinic agonists with a significant increase in intracellular Ca2+ concentration. This may be due to a downregulation of muscarinic receptors (mAChRs) in TSMCs. We report here that the individual component of growth factors or hormones at the concentration used is not sufficient to stimulate growth of TSMCs in the primary culture with 1% fetal bovine serum (FBS). In the presence of 1% FBS, TSMCs withdraw from the cell cycle and express high levels of cell surface mAChRs. Furthermore, insulin-like growth factor I (IGF-I) and insulin (Ins), alone or in combination, could stimulate the expression of mAChRs on the cultured TSMCs in 1% FBS without changing the affinity of receptors. Heparin could inhibit these stimulatory effects on mAChR expression. The pharmacological response of functional mAChRs, determined as accumulation of inositol phosphates induced by carbachol, is greater in the medium containing IGF-I and Ins than those cultured in 1% FBS. This action may be partially mediated through a cholera toxin-sensitive protein. The results conclude that IGF-I and Ins are necessary for TSMCs to express functional mAChRs.

Muscarinic receptor expression in the primary culture of tracheal smooth muscle cells

Tracheal smooth muscle cells (TSMCs) were isolated from dog trachea in order to analyze the direct effects of growth factors and hormones on cell proliferation and muscarinic receptor (mAchR) expression. Dissection and dissociation of tracheal smooth muscle tissue with a collagenase I, deoxyribonuclease I and elastase IV mixture resulted in high yield and viability of TSMCs. A screen of growth factors, hormones, and serum concentration for the stimulation of cell growth, revealed that insulin-like growth factor, basic fibroblast growth factor, epidermal growth factor, insulin, transferrin, or hydrocortisone alone at the concentration used was not necessary or sufficient to stimulate growth of TSMCs in the primary culture with DMEM/F-12 containing 1% FBS. The regulation of cell surface mAchR expression in response to serum and cell growth in primary culture of TSMCs has been examined. In the presence of 1% serum, TSMCs withdraw from the cell cycle and express high levels of cell surface mAchRs. Exposure of quiescent TSMCs to 10% serum results in a loss of surface mAchRs. In addition, insulin-like growth factor, insulin or transferrin could stimulate the expression of mAchRs on TSMCs cultured in DMEM/F-12 containing 1% FBS. The results demonstrated that low serum concentration culture system may provide a useful model to elucidate the expression of mAchRs in the culture of TSMCs.

Development and characterization of primary cultures of smooth muscle cells from the fibromuscular stroma of the guinea pig prostate

Primary cultures of smooth muscle cells (SMCs) were obtained by a two-step enzymatic digestion of guinea pig prostatic stroma. Ultrastructural morphology and growth characteristics of these cells conformed to those reported for SMCs isolated from vascular and visceral tissue sources. Electron microscopic examination indicated that the cells assumed modified myofibroblastoid features in culture. Microfilaments with associated dense bodies were markedly depleted in cultured smooth muscle cells, in comparison with those of the parent tissue. Cultured cells also possessed increased content of rough endoplasmic reticulum indicating the increased secretory or protein-synthetic capacity of the cells. Immunoperoxidase staining for cytoskeletal markers using monoclonal antibodies to desmin and vimentin supported the ultrastructural observations, suggesting a decline in desmin-staining intermediate filaments during "modulation" to the myofibroblastoid form. Despite this depletion of smooth muscle-specific differentiation markers and reversion to more general mesenchymal properties, the cells retained the ability to contract on challenge with norepinephrine, and grew in the characteristic "hill and valley" pattern on attaining confluence. Inasmuch as the estrogen and androgen receptor expression of the parent stromal tissue is also retained, these primary cell cultures should provide a useful model to study regulation of prostatic development.