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Biomedical subjects

C W Emala

Publications and source records attributed to C W Emala.

8 recordsLinked to original sources
PubMed1995

Reduced adenylyl cyclase activation with no decrease in beta-adrenergic receptors in basenji greyhound leukocytes: relevance to beta-adrenergic responses in airway smooth muscle.

Mononuclear leukocytes (MNLs) have been used as a model of beta-adrenergic responsiveness of airway smooth muscle, but the relevance of this model remains controversial. The basenji greyhound (BG) dog model of airway hyperresponsiveness shares some features with human asthma, and airway smooth muscle shows a selective impairment in isoproterenol-stimulated adenylyl cyclase activity. In this study, MNL membranes were obtained from these same dogs, and the beta-adrenergic receptor-adenylyl cyclase cascade function was compared with that in airway smooth muscle. beta-Adrenergic receptor numbers and affinities for iodine 125-cyanopindolol were similar in the two dog groups (receptor numbers [Bmax] = 441 +/- 101 and 447 +/- 61 fmol/mg protein and dissociation constant [Kd] = 269 +/- 44 and 312 +/- 60 pmol/L for mongrel and BG MNLs, respectively). Quantities of the Gs alpha protein were not different in the membranes as determined by immunoblotting. Stimulation of adenylyl cyclase by isoproterenol (100 mumol/L) was impaired in MNL membranes of BG membranes (22% +/- 4% increase over guanosine triphosphate [10 mumol/L]) compared with mongrel membranes (47% +/- 8.6% increase over guanosine triphosphate [10 mumol/L], p < 0.05). Stimulation of adenylyl cyclase by prostaglandin E1 (10 mumol/L), NaF (10 mmol/L), or forskolin (10 mumol/L) did not differ in membranes from the two groups. No difference was found in the lymphocyte subsets in the two groups as determined by flow cytometry. These findings are qualitatively similar to studies of trachealis muscle membranes from these same dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1995

Expression of muscarinic receptor subtypes and M2-muscarinic inhibition of adenylyl cyclase in lung.

The relative distribution and absolute quantities of muscarinic receptor subtypes m1, m2, m3, and m4 were determined in membranes of canine trachealis muscle, bronchi, and lung parenchyma by immuno-precipitation with receptor subtype-specific rabbit polyclonal antisera. Additionally, the functional coupling of muscarinic receptors to the inhibition of adenylyl cyclase was related to the presence of m2-muscarinic receptors in each region. Immunoprecipitation identified more total muscarinic receptors in trachealis muscle than in bronchi or lung. m2-Muscarinic receptor predominated in tracheal muscle (372 +/- 85 fmol/mg protein) with fewer m3 receptors (48 +/- 5 fmol/mg protein). Bronchi contained 6.6 +/- 2.0 and 9.2 +/- 1.8 fmol/mg protein of m2 and m3 receptors, respectively. Lung parenchyma contained 13.9 +/- 3.9 fmol/mg protein of m3 receptors. Adenylyl cyclase activity increased in response to guanosine triphosphate and isoproterenol in membranes from all three lung regions, but muscarinic-mediated inhibition of adenylyl cyclase occurred only in trachealis membranes. These studies provide the first quantitative assessment of muscarinic receptor subtypes in different regions of the lung and relate the ability to measure muscarinic inhibition of adenylyl cyclase to the presence of m2 receptors.

Acetylcholine↗
PubMed1995

Basenji-greyhound dog: increased m2 muscarinic receptor expression in trachealis muscle.

Airway smooth muscle from asthmatic humans and from the Basenji-greyhound dog (BG) dog is hyporesponsive to beta-adrenergic agonist stimulation. Because adenylyl cyclase is under dual regulation in airway smooth muscle, we compared muscarinic receptor-coupled inhibition of adenylyl cyclase in airway smooth muscle from BG and mongrel dogs. Inhibition of forskolin-stimulated adenylyl cyclase activity by the muscarinic M2 agonist oxotremorine was greater in airway smooth muscle membranes from BG compared with mongrel controls. Quantitative immunoprecipitation studies showed increased numbers of m2 but not m3 muscarinic receptors in the BG airway smooth muscle. The enhanced ability of muscarinic agonists to inhibit adenylyl cyclase in BG airway smooth muscle may be due to the greater numbers of muscarinic m2 receptors, which may account in part for impaired airway smooth muscle relaxation in the BG model of airway hyperresponsiveness.

Adenylyl Cyclase Inhibitors↗
PubMed1994

G protein subunits in lung cells.

Many hormones and neurotransmitters bind to membrane-bound receptors that are coupled to signal generating enzymes or ion channels via signal transducing GTP-binding proteins termed G proteins. Although receptors and second messengers have been extensively studied in cells of the respiratory system, the G proteins responsible for the coupling of these proteins have not been well-characterized. Therefore, we used immunoblot analysis to determine expression of G protein alpha and beta subunits in membranes prepared from cells and tissues of the respiratory system, including cultured canine tracheal epithelium, cleanly dissected canine tracheal smooth muscle, canine large conducting airways, and canine and human lung parenchyma. The two isoforms of Gs alpha (45 and 52 kDa) were present in all tissues, with a predominant expression of the 45 kDa isoform. Plasma membranes prepared from canine tracheal epithelium and muscle, and human lung parenchyma, contained greater amounts of Gs alpha than membranes prepared from canine bronchus and lung. Relative levels of immunoreactive G(i) alpha(2), G(i) alpha(3), Gq/G11 alpha, beta 1 and beta 2 were similar in all of the tissues studied. By contrast, G(o) alpha was absent in cultured tracheal epithelium, and tracheal smooth muscle expressed greater amounts of G(i) alpha(2) compared to G(i) alpha(3). Specificity of G protein expression can provide one regulatory mechanism for functional biochemical pathways within cells. The demonstration of specific G protein subunits is the first step in the molecular characterization of the regulation of these pathways, both in normal tissues and in disease states.

Amino Acid Sequence↗
PubMed1994

Signal-transducing G proteins: basic and clinical implications.

The pivotal role that G proteins play in transmembrane signal transduction is highlighted by the rapidly expanding list of receptors and effector molecules that are coupled through G proteins. G proteins are poised to allow discrimination and diversification of cellular signals into the cytosolic milieu. The utilization of an evolutionarily conserved "GTPase clock" by G proteins, offers insight into the fundamental role these proteins play in biology. Knowledge of the implication of altered expression or function of G proteins in human disease is now emerging. It is not surprising that deficiency or expression of altered forms of these important proteins can lead to global or restricted metabolic disturbances, depending upon the distribution and role of the G protein. Human disorders, including heart failure, alcoholism, endocrine abnormalities, and neoplasia, are now recognized as due in part to altered expression or function of G proteins.

Amino Acid Sequence↗
PubMed1994

Characterization of GTP-binding proteins coupled to inhibition of adenylyl cyclase in guinea pig tracheal epithelial cells.

Many important airway epithelial cell functions are regulated by intracellular cAMP. Adenylyl cyclase, the enzyme that synthesizes cAMP, is under dual regulation in many cells, but muscarinic agonists have not been shown to inhibit adenylyl cyclase in human and dog epithelial cells, despite the presence of muscarinic receptors. We question whether the lack of inhibition was related to the absence of a component of the inhibitory pathway or a lack of coupling between the components. The GTP-binding regulatory proteins (G proteins) that regulate adenylyl cyclase activity in airway epithelium have not been well characterized. We used primary cultures of guinea pig tracheal epithelial cells as a model system and identified the G proteins that modulate adenylyl cyclase activity. Immunoblot analysis demonstrated the presence of alpha subunits corresponding to stimulatory (Gs alpha) and inhibitory [Gi alpha (2) and Gi alpha (3)] G proteins as well as beta chains. These G proteins were functionally coupled to stimulation and inhibition of adenylyl cyclase in epithelial membrane preparations. Pertussis toxin-catalyzed [32P]ADP-ribosylation of Gi alpha was significantly reduced by 100 microM GTP gamma S (78.4 +/- 3.6% of control), by 100 mM NaF (41.9 +/- 9.1% of control), and by carbachol (100 microM) (29.2 +/- 9.0% of control). Atropine (10 microM) inhibited the carbachol effect by greater than 90%, suggesting that the muscarinic receptors were functionally coupled to Gi proteins. beta-Adrenergic agonists increased adenylyl cyclase activity, but muscarinic agonists failed to inhibit this enzyme. In summary, guinea pig tracheal epithelial membranes contain muscarinic receptors, Gi alpha (2) and adenylyl cyclase, which are appropriately coupled.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗
PubMed1983

Invited review: bacterial flagellar sheaths: structures in search of a function.

Although bacterial flagellar sheaths were observed over 30 years ago, they may still be characterized as structures in search of a function. In addition to true sheaths, bacterial flagella may possess other adornments that cause an increase in the organelle's cross-sectional diameter. These "complex flagella" are sharply differentiated from sheathed flagella. Immunological and chemical distinctions have been found between flagellar sheaths, flagellar cores, and LPS layers inferred to be the sheath sensu stricto. Although complex flagella may serve as specific receptors for flagellotropic phages or in allowing for more efficient swimming in viscous environments, similar functions have not yet been attributed to true sheaths. It is postulated that flagellar sheaths may allow for specific interaction between a bacterium and a surface. In addition, there is a problem as to the relationship between a rapidly rotating flagellum and the sheath.

Antigens, Bacterial↗