Extracellular calcium and human isolated airway muscle: ionophore A23187 induced contraction

Dynamics of airway response in lung microsections: a tool for studying airway-extra cellular matrix interactions

The biological configuration of extracellular matrix (ECM) plays a key role in how mechanical interactions of the airway with its parenchymal attachments affect the dynamics of airway responses in different pulmonary disorders including asthma, emphysema and chronic bronchitis. It is now recognized that mechanical interactions between airway tissue and ECM play a key regulatory role on airway physiology and kinetics that can lead to the reorganization and remodeling of airway connective tissue. A connective tissue is composed of airway smooth muscle cells (ASM) and the ECM, which includes variety of glycoproteins and therefore the extent of interactions between ECM and ASM affects airway dynamics during exacerbations of major pulmonary disorders. Measurement of the velocity and magnitude of airway closure or opening provide important insights into the functions of the airway contractile apparatus and the interactions with its surrounding connective tissues. This review highlights suitability of lung microsection technique in studying measurements of airway dynamics (narrowing/opening) and associated structural distortions in airway compartments.

Lipid Emulsion Attenuates Acetylcholine-Induced Relaxation in Isolated Rat Aorta

We investigated the effect of Lipofundin MCT/LCT and Intralipid on acetylcholine-induced nitric oxide- (NO-) mediated relaxation in rat aorta to determine which lipid emulsion (LE) is more potent in terms of inhibition of NO-induced relaxation. Dose-response curves of responses induced by acetylcholine, the calcium ionophore A23187, and sodium nitroprusside were generated using isolated rat aorta with or without LE. The effect of Lipofundin MCT/LCT on acetylcholine-induced endothelial nitric oxide synthase (eNOS) phosphorylation in human umbilical vein endothelial cells (HUVECs) was investigated using western blotting. Lipofundin MCT/LCT (0.1 and 0.2%) attenuated acetylcholine-induced relaxation in endothelium-intact aorta with or without tiron, whereas 0.2% Intralipid only inhibited relaxation. Lipofundin MCT/LCT inhibited relaxation induced by the calcium ionophore A23187 and sodium nitroprusside in endothelium-intact aorta, but Lipofundin MCT/LCT had no effect on sodium nitroprusside-induced relaxation in the endothelium-denuded aorta. Combined pretreatment with l-arginine plus Lipofundin MCT/LCT increased acetylcholine-induced maximal relaxation in endothelium-intact aorta compared with Lipofundin MCT/LCT alone. l-Arginine attenuated Lipofundin MCT/LCT-mediated inhibition of acetylcholine-induced eNOS phosphorylation in HUVECs. Taken together, Lipofundin MCT/LCT attenuated acetylcholine-induced NO-mediated relaxation via an inhibitory effect on the endothelium including eNOS, which is proximal to activation of guanylyl cyclase.

Activation properties of chemically skinned fibres from human isolated bronchial smooth muscle

1. The contractile activation properties of human isolated bronchial smooth muscle were investigated using chemically (beta-escin) skinned strips. 2. Concentration-dependent contractions were induced by free ion concentrations of Ca2+ (0.5-3 microM), Sr2+ (2-200 microM) and Ba2+ (50-1000 microM). The resulting -log[cation]-tension relationships were fitted by sigmoidal curves with EC50 values (cation concentration required to produce half-maximal tension) and co-operativity factors (Hill coefficient, nH) of, respectively, 0.25 microM and 3.4 for Ca2+, 12 microM and 2.64 for Sr2+ and 100 microM and 1.73 for Ba2+. Maximal responses to Sr2+ and Ba2+ were 125.5 +/- 15.4 and 96 +/- 8.1% (n = 5) respectively of the maximum tension induced by Ca2+. 3. Trifluoperazine (5-100 microM), cyclic AMP (50-300 microM) and cyclic GMP (50-100 microM) each antagonized Ca2+ in a concentration-dependent manner. On the other hand, okadaic acid (OA, 0.2-1 microM) potentiated Ca2+ and increased the maximum response to Ca2+ (+25 +/- 5.4%, n = 5, for 1 microM OA). 4. This study has demonstrated the high Ca2+ sensitivity of the activation mechanism of human isolated bronchial smooth muscle. It also suggests that control of the contractile machinery in the human bronchus involves processes of phosphorylation and dephosphorylation. The beta-escin-treated human bronchus may be a useful model for investigating the cellular basis of some pathophysiological processes such as bronchial hyper-responsiveness.

The effect of EDTA on contractile responses of guinea-pig trachea in calcium-free medium and on the recovery of the contractile responses in calcium-containing solution

1. Acetylcholine (0.1 mmol/l) and KCl (80 mmol/l) induce contractile responses in guinea-pig trachea. 2. In the absence of extracellular Ca, contractile responses to ACh or KCl decrease as the preincubation time or the EDTA concentration increases. 3. Exposure of the tissue to Ca-free medium decreases the basal tone. 4. Prolonged incubation in the presence of EDTA (1 mmol/l) promotes a delay in the recovery of the tonic component of the contraction elicited subsequently by acetylcholine and KCl in physiological salt solution, and abolishes the phasic one.

Sensitization decreases relaxation in human isolated airways

Passively sensitized human isolated airways provide an opportunity to study some aspects of bronchial hyperresponsiveness in vitro. Since it has been suggested that excessive airway narrowing could be due to impaired relaxation, we examined the effect of a variety of agents producing relaxation via different mechanisms, i.e., verapamil and lemakalim (a calcium channel antagonist and a potassium channel opener, respectively) and isoproterenol, forskolin, and dibutyryl cAMP (modulators of the beta-adrenoceptor signal transduction pathway). Human bronchial rings, obtained at thoracotomy, were passively sensitized by incubation in serum from atopic asthmatic patients, and control rings were incubated in serum from nonatopic subjects. We also studied bronchial rings from five spontaneously sensitized human lung specimens. Responses to the relaxant compounds were measured isometrically. Passive sensitization significantly decreased the efficacy of verapamil in maximally contracted tissues from 60 +/- 10 to 45 +/- 7% of the maximal carbachol response (n = 6, p < 0.05) and that of lemakalim from 51 +/- 16 to 38 +/- 14% (n = 7, p < 0.05) in tissues at baseline tone. Similarly, spontaneously sensitized tissues relaxed less to lemakalim (64 +/- 6% of the maximal response to isoproterenol, n = 5, p < 0.05) than did nonsensitized tissues (80 +/- 4%). Sensitization did not alter responses to isoproterenol, forskolin, and dibutyryl cAMP. We conclude that sensitization of human isolated airways reduces relaxation responses that depend upon activation of ion channels but not those that depend upon activation of beta-adrenoceptors and transduction processes directly coupled to these receptors.

Effect of in vitro exposure to acrolein on carbachol responses in rat trachealis muscle

Isolated tracheal rings obtained from male Wistar rats 10 to 15 weeks old and weighing 300 to 400 g were exposed to aqueous solutions of acrolein, and the resulting change of smooth muscle contractility was evaluated by measuring the cumulative carbachol concentration-response curve. Using the product of acrolein concentration and time as a surrogate for the acrolein dose delivered to the smooth muscle cells, contractility measured after a variety of exposure concentrations from 0.01 to 3.0 microM and times from 5 to 60 min could be correlated in a dose-dependent manner. In the range of doses from 0.1 to 6 microM-min, relative contractility continuously increased from 0 to 50% above unexposed control values. At doses greater than 6 microM-min, the enhancement in contractility declined. This decline may have been due to cell damage or cell death which was so severe at a dose of 60 microM-min that contractility fell below control values. Below a threshold dose of 0.1 microM-min, acrolein had no effect on contractility. The role arachidonic acid metabolism in the enhancement of smooth muscle reactivity to carbachol was studied using indometacin to block the cyclo-oxygenase pathway and NDGA to block the lipoxygenase pathway. At a concentration of 10 microM of either indometacin or NDGA, the acrolein-induced enhancement in airway reactivity was completely inhibited. At lower concentrations, inhibition by these two chemicals was partially additive, suggesting that both the lipoxygenase and cyclo-oxygenase pathways play a role in the hyperreactive response.

Responsiveness to histamine in human sensitized airway smooth muscle

Passive sensitization of human isolated airway smooth muscle increases contractile responses to histamine. We looked to see whether this increase was due to an alteration in the relative role of histamine H1 and H2 receptors. Human bronchial spiral strips obtained at thoracotomy were passively sensitized by incubation in serum from atopic asthmatic patients to Dermatophagoïdes pteronyssinus and control strips were incubated in serum from healthy non-allergic non-atopic subjects. We also studied spiral strips dissected from two spontaneously sensitized human lung specimens. Cumulative concentration-response curves (CCRC) to Ca2+ (10(-5) -3 x 10(-2) M) were constructed either in the presence of 10(-5) M histamine alone or in that of the combination histamine and the H2 antagonist cimetidine (10(-5) M). Unlike in the absence of histamine, Ca2+ CCRC in the presence of histamine alone were significantly shifted to the left in the passively sensitized tissues (mean EC50: 5.7 x 10(-4) M) compared to control ones (mean EC50: 9.3 x 10(-4) M, n = 6, P < 0.05). Addition of cimetidine to histamine did not alter the Ca2+ CCRC either in the control or in passively or spontaneously sensitized airway smooth muscle. These results suggest that (i) passive sensitization increases contractile response to Ca2+ of human bronchial smooth muscle in the presence of histamine; (ii) this increase is not due to a difference in the H1- vs H2-mediated response; and (iii) H2-mediated effects do not play a significant role in spontaneously sensitized human lung as both in the non-sensitized and passively sensitized lung.

[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.

Characterization of contractile prostanoid receptors on human airway smooth muscle

In human bronchial rings the thromboxane A2 (TxA2) mimetic, U46619, produced cumulative concentration-related contractions up to a maximum of 141 +/- 23% of the response induced by carbachol or acetylcholine. The geometric mean EC50 value was 3.2 X 10(-8) M (95% confidence interval: 1.2, 8.9 X 10(-8) M) (n = 5). Contractions to U46619 were unaffected by atropine (10(-6) M) or verapamil (10(-5) M), but were competitively antagonized by the TxA2 antagonist GR32191 with a pA2 value of 8.40 +/- 0.41. The maximum contractile response to prostaglandin (PG) F2 alpha was smaller (90 +/- 9%, n = 13) and the potency was less (EC50 = 2 X 10(-6) M) than that of U46619. Contractions to PGF2 alpha were also competitively antagonized by GR32191 with a pA2 value of 8.18 +/- 0.08. Concentration-response curves to PGE2 were biphasic, relaxation at concentrations from 10(-9) to 10(-6) M and contraction from 10(-6) to 3 X 10(-5) M. GR32191 10(-7) M inhibited the contractile portion of the response curve in 8 of 11 tissues. Based on these results we conclude that U46619, PGF2 alpha and PGE2 all contract human airways by stimulation of the TxA2 (TP) receptor.