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At least 181 records · Page 10Linked to original sources
PubMed1981

Reassessment of electrophysiological and contractile characteristics of sensitized airway smooth muscle.

Airway smooth muscle preparations were isolated from control guinea pigs, from animals sensitized to albumin and Pertussis vaccine, from sensitized animals which had been resensitized and from animals that had been sensitized and exposed to an inhalation challenge of albumin for 14 days. The resting membrane potential, its changes and contractile response of airway smooth muscle were measured during in vitro antigen challenge, administration of histamine dihydrochloride (10(-3) M), or isoproterenol (10(-3) M). We have found that: (1) The resting membrane potential of normal airway smooth muscle of guinea pig was -61.3 +/- 0.2 mV (+/- SE); (2) Resting membrane potential of airway smooth muscle from sensitized animals was significantly increased (P less than 0.05) to -72.9 +/- 0.3 mV (+/- SE); (3) One week after resensitization of animals a further significant increase (P less than 0.05) in resting membrane potential to -76.2 +/- 0.2 mV (+/- SE) was observed; (4) Resting membrane potential of airway smooth muscle isolated from animals repeatedly exposed to inhalation challenge of antigen significantly decreased (P less than 0.01) to -50.6 +/- 0.5 mV (+/- SE) as compared to controls; (5) After histamine, isoproterenol or antigen administration, the airway smooth muscle from sensitized animals repeatedly exposed to inhalation challenge showed attenuated response (P less than 0.01) as measured by both membrane potential and isometric force. In contrast, the response to antigen and histamine in preparations from sensitized animals is potentiated. It is concluded that both acute sensitization and resensitization on one hand and repeated exposure of sensitized animals to inhaled albumin on the other will alter cellular mechanism(s) responsible for the maintenance of membrane potential and the regulation of excitation-contraction coupling in airway smooth muscle.

Action Potentials↗
PubMed1992

Disorganization of microfilaments is accompanied by downregulation of alpha-smooth muscle actin isoform mRNA level in cultured vascular smooth muscle cells.

In the previous report, we demonstrated that cAMP negatively regulated alpha-smooth muscle actin mRNA levels through destabilization of the mRNA [O. Ohara et al. (1991) J. Biochem. 109, 834-839]. We here report that the decline in the alpha-smooth muscle actin mRNA levels was well correlated with disorganization of microfilaments but not necessarily with the rise in intracellular cAMP levels in rat cultured vascular smooth muscle cells. The decrease in the alpha-smooth muscle actin mRNA induced by microfilament-disorganizing agents also resulted from enhancement of the turnover rate of the mRNA. These results raise the possibility that the post-transcriptional control of the alpha-smooth muscle actin expression is linked to the organization of actin filaments in smooth muscle cells.

Actin Cytoskeleton↗
PubMed1993

Calponin phosphatase from smooth muscle: a possible role of type 1 protein phosphatase in smooth muscle relaxation.

Smooth muscle myosin bound phosphatase (MBP) purified from chicken gizzard, which is a holoenzyme of type 1 delta protein phosphatase and dephosphorylated intact myosin, catalyzed the dephosphorylation of calponin phosphorylated by protein kinase C (PK-C). The Km of MBP for calponin was 0.6 microM and the Vmax was 350 nmol/min/mg. All of the multiple sites of phosphorylation by PK-C of calponin were completely dephosphorylated by MBP. Functionally, calponin dephosphorylated by MBP recovered its inhibitory effect on the actin-activated Mg(2+)-ATPase activity of myosin. Therefore, these results suggest that a type 1 delta protein phosphatase causes relaxation of smooth muscle by the dephosphorylation not only of myosin but also of calponin.

Animals↗
PubMed1979

Role of calcium and cyclic adenosine 3':5' monophosphate in regulating smooth muscle contraction. Mechanisms of excitation-contraction coupling in smooth muscle.

Caclium initiates smooth muscle contraction by activating an enzyme, myosin light chain kinase. This enzyme catalyzes the transfer of phosphate from adenosine triphosphate to the 20,000 dalton light chain of myosin. In its phosphorylated form myosin interacts with actin to produce muscle contraction. The mechanism by which calcium activates myosin kinase requires (1) the binding of calcium to a 16,500 dalton calcium-binding protein (calmodulin), and (2) the binding of calmodulin-calcium to a 125,000 dalton catalytic subunit. This two protein complex is the active form of myosin light chain kinase. Smooth muscle relaxation is mediated by cyclic adenosine 3':5' monophosphate (cyclic AMP). One nechanism by which the latter may exert a direct effect on actin-myosin interaction is through the activation of a cyclic AMP-dependent protein kinase that can phosphorylate the 125,000 dalton component of myosin light chain kinase. Phosphorylation of myosin light chain kinase decreases the activity of the enzyme, thus favoring the unphosphorylated form of myosin, which cannot interact with actin to produce smooth muscle contraction.

Actins↗
PubMed2001

Tissue-specific expression of an anti-proliferative hybrid transgene from the human smooth muscle alpha-actin promoter suppresses smooth muscle cell proliferation and neointima formation.

The retinoblastoma protein (Rb), a key regulator of cell cycle progression, can bind the transcription factor E2F converting it from a positive transcriptional factor capable of driving cells into S phase into a negative complex which arrests cells in G1. We have created a potent transcriptional repressor of E2F-dependent transcription by fusing the C-terminal fragment of Rb (p56) to the DNA and DP1-binding domains of E2F. Because the expression of E2F/56 fusion protein from a constitutive promoter was incompatible with virus growth, adenovirus constructs were prepared where transgenes were expressed from a fragment of the smooth muscle alpha-actin (SMA) promoter. Immunoblot and beta-galactosidase staining demonstrated smooth muscle-specific expression of this transcriptional element in vitro. The SMA-p56 and SMA-E2F/p56 adenoviral constructs also induced G0/G1 cell cycle arrest specifically in smooth muscle cells. Following administration to rat tissues, the SMA-beta-galactosidase construct exhibited expression in balloon-injured carotid arteries, but not in liver, bladder or skeletal muscle. Local delivery of the SMA-E2F/p56 adenoviral construct to balloon-injured carotid arteries inhibited intimal hyperplasia. Our results demonstrate that local delivery of the SMA-E2F/p56 adenoviral construct can limit intimal hyperplasia in balloon-injured vessels, while avoiding toxicity that could occur from the dissemination and expression of the viral transgene.

Actins↗
PubMedDate not supplied

[Cellular mechanism of muscle contraction of bronchial smooth muscle].

Airway smooth muscle is one of the main effector of bronchial reactivity. The understanding of the cellular mechanisms involved in the contraction of this muscle has advanced in the recent past since isolated cells in culture can now be studied. Extracellular messengers (neurotransmitters and mediators) as well as their specific membrane receptors have been analyzed in some details. The membrane transduction of extracellular messengers brings about the formation (or the increase in the concentration) of the intracellular second messenger which, in airway smooth muscle, is the cytosolic calcium (Ca2+i) via activation of calcium channels which depend on surface membrane potential changes (electromechanical coupling) on the one hand and mainly via mechanisms independent of surface membrane potential changes-so-called the pharmacomechanical coupling--which involves membrane phosphoinositides metabolism. Changes in Ca2+i activate contractile proteins leading the muscle to shorten and to develop force via several controlled steps such as phosphorylation of myosin or changes in the sensitivity to Ca2+ of the contractile elements. Experimental techniques that enable to simultaneously study different aspects of the cellular response are being developed in airway smooth muscle and are likely to provide complementary information about the cellular physiology and pathophysiology of this muscle.

Animals↗
PubMed1999

Localization of 17-kDa myosin light chain isoforms in cultured aortic smooth muscle cells.

Smooth muscle myosin II contains two 17-kDa essential light chain isoforms (LC17gi and LC17nm) of which the relative contents differ among myosins. To understand the roles of LC17 isoforms in the functions of myosin, we performed an immunofluorescence microscopic examination of their localization in primary cultured cells isolated from rat aortic smooth muscle. To identify the isoforms, rabbit polyclonal antibodies were prepared against C-terminal nonapeptides corresponding to either LC17gi or LC17nm from porcine aortic smooth muscle myosin. These isoforms differ in only 5 amino acid residues within the C-terminal 9 residues. These antibodies specifically recognize each LC17 isoform on urea-PAGE of total rat aortic cell lysates. Immediately after plating, the smooth muscle cells stained heterogeneously with each antibody, indicating differing contents of LC17 isoforms among cells. On double staining 1-2 d cultures with both antibodies, LC17nm was detected diffusely throughout the cytoplasm, whereas LC17gi was concentrated in specific regions such as the cell periphery and the base of cytoplasmic processes. These results support the suggestion that myosin containing LC17gi is essential for force-generation by aortic smooth muscle and that myosin containing LC17nm may play an important role in maintaining smooth muscle tension.

Animals↗
PubMed1991

Impedance analysis applicable to cardiac muscle and smooth muscle bundles.

An electrical equivalent circuit was constructed to represent a chain of five myocardial cells in a cardiac muscle bundle with various degrees of cell-to-cell coupling, and an impedance analysis was performed. The impedance across the entire network was measured at frequencies ranging from 10(1) to 10(6) Hz. The Bode plots were nearly superimposable for 1, 10, and 100 tunnels; for 10(3), 10(4), and 10(5) tunnels, the absolute zeta at 10 Hz was lower: e.g., 9.82 M omega for 1 tunnel compared to 6.64 M omega for 10(5) tunnels. The delta zeta 1/2 values were shifted to the left in the well-coupled cases: e.g., for 1 tunnel, f1/2 was 37.8 kHz, and for 10(5) tunnels, f1/2 was 1.2 kHz. For high coupling, the Bode plots contained a double component due to the end membranes. When Ro was increased by eight times, zeta increased by 7.47 fold (for 1 tunnel, 10 Hz), and by 3.72 fold (for 10(5) tunnels, 10 Hz). Raising Ro to x 12, x 100, and x 1000 produced a further and further shift to the left of the Bode plots. The total tissue resistivity (Rt) increased as a function Ro. Thus, in low coupling cases, almost all of the applied current passes through the interstitial space; e.g., at 1 tunnel (10 Hz), 1.0% of the current passes through the cell pathway (Rcell). The ratio of impedances at 10 kHz to 10 Hz (zeta 10kHz/zeta 10Hz) decreased with increasing tunnels (for Ro x 1). The ratio of resistivities at Ro x 8 to Ro x 1 (Rt'/Rt) was 7.47 for 1 tunnel. In contrast, the ratio at 10(5) tunnels was 3.73. It is concluded that it is difficult to determine the degree of cell coupling from such impedance analysis, unless the same tissue can be used for its own control, i.e., before and after a large change in cell coupling is introduced.

Cell Communication↗
PubMed1986

Effect of methylated bepridil on slow action potentials in cardiac muscle and vascular smooth muscle.

The anti-anginal agent bepridil blocks slow Ca2+ channels in a variety of tissues. Since bepridil accumulates inside cells, the possibility exists that bepridil acts, at least partially, from inside the cell. To test this possibility, we examined the effects of a quaternary ammonium analog of bepridil, methylated bepridil, which presumably would enter the cells less readily, on the Ca2+-dependent slow action potentials of guinea pig papillary muscles (in 25 mM [K+]0) and rabbit pulmonary arteries (in tetraethylammonium chloride). In cardiac muscle, methylated bepridil had little effect on the slow action potentials at low stimulation frequencies (0.5 Hz), but at higher frequencies (1.0 and 2.0 Hz) the slow action potentials were depressed and/or the muscle was unable to follow each stimulation. These effects are similar to those obtained with bepridil, but bepridil was more potent than methylated bepridil. In vascular smooth muscle cells, methylated bepridil inhibited the slow action potentials at a somewhat lower dose than bepridil. We conclude that, in cardiac muscle, bepridil probably has two sites of action, one outside the cell (presumably on or associated with the slow Ca2+ channel) and a second site inside the cell. On the other hand, in vascular smooth muscle cells, bepridil may act only on an external site.

Action Potentials↗
PubMed1996

Smooth muscle alpha-actin downregulation in cultured chick aortic smooth muscle and neural crest cells is associated with altered cell shape.

A modified CXL retrovirus was used to clone an antisense smooth muscle alpha-actin ribozyme sequence adjacent to the reporter lacZ sequence. The virus was applied to downregulate alpha-actin expression in cultured smooth muscle cells obtained from chicken aortic arch and cultured neural crest cells. After infection with the ribozyme-containing CXL retrovirus both the smooth muscle and neural crest cells showed beta-galactosidase activity accompanied by a reduction of smooth muscle alpha-actin-positive fibers. Double staining of beta-galactosidase and smooth muscle alpha-actin using immunohistochemistry revealed that single cells infected with the CXL/ribozyme showed little to no smooth muscle alpha-actin protein. The absence of smooth muscle alpha-actin was associated with a distinct change in cellular morphology of the cultured cells, suggesting that expression of smooth muscle alpha-actin in cultured neural crest cells may be associated with cytoskeletal elements rather than vascular smooth muscle phenotype.

Actins↗
PubMed1997

Endothelin-1 alters the contractile phenotype of cultured embryonic smooth muscle cells.

Smooth muscle tissues may be classified into phasic (fast) or tonic (slow) contractile phenotypes. This study was initiated to examine the specification of these phenotypes during development and the role of growth factors in this process. We used myosin light chain 17 (MLC17) and myosin heavy chain transcript splice variants as markers of the tonic (aortic) and phasic (intestinal) smooth muscle phenotypes in chick embryos. By reverse transcription-polymerase chain reaction, we determined embryonic days 6 to 16 to be a critical period for the establishment of these phenotypes. During this period, endothelin-1 is present at 40-fold-higher levels in aortic compared with intestinal tissues. To test the hypothesis that endothelin-1 may be involved in establishing the aortic (tonic) phenotype, we developed a system in which embryonic smooth muscle cells exhibit phasic and tonic contractile properties in vitro. Single-cell force measurements showed that cultured embryonic gizzard (phasic) cells developed force more rapidly (8 +/- 2 seconds) and achieved greater force (3.0 +/- 0.7 microN) than did cultured embryonic aortic (tonic) cells (20 +/- 0.7 seconds, 0.76 +/- 0.01 microN; P < .05) in response to depolarization. Chronic exposure of the phasic (gizzard) cells to endothelin-1 prolonged the time to peak force (24 +/- 3 seconds) and reduced the peak force (1.0 +/- 0.1 microN), so that the contraction resembled the tonic type. This effect, mediated by the endothelin-A receptor, was associated with a shift in MLC17 splicing to the tonic pattern. These results demonstrate that endothelin-1 is highly enriched in developing aortic compared with intestinal tissues and can convert phasic smooth muscle cells to the tonic type in vitro, suggesting a role for this growth factor during development in determining the contractile phenotype of smooth muscle cells.

Angiotensin II↗
PubMed2002

Calcium release events in excitation-contraction coupling in smooth muscle.

Although smooth muscle cells are not organized in sarcomeres, as are striated muscles, nevertheless Ca2+ for contraction is released from the sarcoplasmic reticulum (SR) at certain preferred sites. These sites commonly discharge packets of Ca2+ spontaneously and have been called frequent discharge sites (FDSs). Each spontaneous release of a Ca2+ packet usually leads to a burst of openings of Ca2+-activated K+ channels in the cell membrane which produces a spontaneous transient outward current (STOC) in smooth muscle cells under voltage clamp. When fluorescent Ca2+ indicators such as Fluo-3 became available, the spontaneous transient increases in [Ca2+]i produced by Ca2+ packets released from the SR were also detected in cardiac muscle as flashes of fluorescence or 'sparks'. Sparks in smooth muscle consist of smaller Ca2+ packets that can give rise to 'microsparks'. In some smooth muscles which have Ca2+-activated Cl- channels, STICs (spontaneous transient inward currents) are also found to be associated with sparks. FDSs have been found to be important initiating sites for a Ca2+ wave in response to an action potential or in response to receptor activation and possibly other stimuli, such as stretch. In both cases Ca2+-induced Ca2+ release seems to be crucially involved.

Animals↗
PubMed2004

Cell cycle-mediated regulation of smooth muscle alpha-actin gene transcription in fibroblasts and vascular smooth muscle cells involves multiple adenovirus E1A-interacting cofactors.

Expression of smooth muscle alpha-actin in growth factor-induced myofibroblasts and in differentiated vascular smooth muscle cells is transcriptionally controlled by multiple positive or negative trans-acting factors interacting with distinct cis-elements in the 5'-flanking region of the gene. Because none of the transcriptional regulators reported to date is smooth muscle cell- or myofibroblast-specific per se, the dynamic interplay among many factors interacting at specific sites along the promoter appears to be a signature feature of smooth muscle alpha-actin gene regulation in these cell types. Herein, the ability of the adenovirus E1A 12 S protein to bind and functionally inactivate specific cell regulatory factors has been exploited to identify several previously unknown coactivators of the mouse smooth muscle alpha-actin promoter in rodent fibroblasts and vascular smooth muscle cells. In transient cotransfection assays, ectopic expression of wild type E1A suppressed promoter activity in a dose- and cis-element-dependent manner. In asynchronous cells, N-terminal E1A mutants defective in CREB-binding protein (CBP) and p300 binding capacity exhibited markedly reduced inhibitory activity toward a smooth muscle alpha-actin promoter driven by a composite TEF-1-, SRF-, and Sp1/3-regulated enhancer. In synchronized cells, however, a more complex mutant E1A inhibitory pattern indicated that collaboration between CBP/p300 and the retinoblastoma family of pocket proteins was required to produce a fully functional enhancer. Cotransfection experiments conducted with Rb(-/-) fibroblasts demonstrated the necessity of pRB in augmenting smooth muscle alpha-actin enhancer/promoter activity. Physical interaction studies with the use of purified wild type and mutant E1A proteins confirmed that CBP, p300, and pRB were targets of E1A binding in nuclear extracts of vascular smooth muscle cells and/or fibroblasts. Collectively, these results suggest that a repertoire of E1A-interacting proteins, namely CBP/p300 and pRB, serve to integrate the activities of multiple trans-acting factors to control smooth muscle alpha-actin gene transcription in a cell type- and cell cycle-dependent manner.

Actins↗
PubMed1998

Pharmacology of airway smooth muscle.

Airway smooth muscle contributes to changes in airway caliber not only through the variations in its tone but also through its contribution to thickness of the airway wall. Until recently, most attention was paid to the agents that altered airway smooth muscle tone, their receptors, the signal transduction pathways they activated, and the mechanisms of contraction and relaxation themselves. Lately, the regulation of smooth muscle proliferation has received increasing attention, and, most recently, the possible role of smooth muscle as a source of inflammatory mediators has been recognized. Airway smooth muscle cells are now seen as playing an important interactive role with inflammatory and structural cells in the response to injury and repair of the airways.

Asthma↗
PubMed1991

The calpain-calpastatin system in vascular smooth muscle.

Vascular smooth muscle contains large amounts of the Ca(2+)-dependent protease calpain II. In this study, we compared bovine aortic muscle (muscle phenotype) to cultured bovine aortic cells of smooth muscle origin (modulated phenotype) with respect to major constituents of the calpain-calpastatin system. Bovine aortic muscle contained only calpain II by activity measurements, Western blot of tissue extracts and Northern blot of poly(A)+ RNA. On the other hand, using the same methodologies, both calpains I and II as well as the 110 kDa inhibitor protein, calpastatin, were identified in cultured bovine aortic cells of smooth muscle origin. We conclude that the phenotypic state of smooth muscle cells is associated with differential expression of major components of the calpain-calpastatin system. Moreover, bovine aortic muscle is the only tissue identified to date that contains calpain II exclusively.

Animals↗
PubMed1994

Ontogeny of the ryanodine receptor in rabbit urinary bladder smooth muscle.

Bladder smooth muscle contraction is mediated by both direct calcium entry through the cell membrane, and by calcium induced calcium release (CICR) from the sarcoplasmic reticulum (SR) storage sites. Ryanodine is a neutral plant alkaloid which binds to an ion channel located on the SR membrane. Its effects in cardiac skeletal muscle are well characterized where it inhibits the efflux of intracellular calcium stores, and thus it serves as a negative inotrope. It has also been shown that in the developing rabbit myocardium, there is a gradual increase in the expression of this ion channel. Little has been written about the expression and function of the ryanodine sensitive ion channel in smooth muscle. Recently we have shown that neonatal rabbit bladder smooth muscle is not very sensitive to ryanodine, while that from mature rabbits is extremely sensitive. This leads us to quantify the expression of the ryanodine sensitive ion channel. In this paper we demonstrate that the Kd values do not change to any significant degree with normal rabbit bladder development. However the Bmax values for 3 day, 2, 4, 6, and 8 week rabbit bladder smooth muscle are 7, 10, 15, 29, and 44 fmol specifically bound ryanodine/mg protein. The differences between the neonatal groups and the mature groups are significant (P < 0.5). This increase in ryanodine sensitive ion channel expression with normal growth would suggest that with normal maturation, the bladder smooth muscle cell acquires an increased pool of sequestered intracellular calcium. This would follow a similar pattern of development that has already been described in rabbit myocardium.

Aging↗