Phenotypic diversity and molecular mechanisms of airway smooth muscle proliferation in asthma

Epoxyeicosatrienoic acids (EETs) are produced from arachidonic acid via the cytochrome P-450 epoxygenase pathway. EETs are able to modulate smooth muscle tone by increasing K+ conductance, hence generating hyperpolarization of the tissues. However, the molecular mechanisms by which EETs induce smooth muscle relaxation are not fully understood. In the present study, the effects of EETs on airway smooth muscle (ASM) were investigated using three electrophysiological techniques. 8,9-EET and 14,15-EET induced concentration-dependent relaxations of the ASM precontracted with a muscarinc agonist (carbamylcholine chloride), and these relaxations were partly inhibited by 10 nM iberiotoxin (IbTX), a specific large-conductance Ca2+-activated K+ (BKCa) channel blocker. Moreover, 3 μM 8,9- or 14,15-EET induced hyperpolarizations of −12 ± 3.5 and −16 ± 3 mV, with EC50 values of 0.13 and 0.14 μM, respectively, which were either reversed or blocked on addition of 10 nM IbTX. These results indicate that BKCa channels are involved in hyperpolarization and participate in the relaxation of ASM. In addition, complementary experiments demonstrated that 8,9- and 14,15-EET activate reconstituted BKCa channels at low free Ca2+ concentrations without affecting their unitary conductance. These increases in channel activity were IbTX sensitive and correlated well with the IbTX-sensitive hyperpolarization and relaxation of ASM. Together these results support the view that, in ASM, the EETs act through an epithelium-derived hyperpolarizing factorlike effect.

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Autocrine production of matrix metalloproteinase-2 is required for human airway smooth muscle proliferation

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1999.277.6.l1109 ◽

1999 ◽

Vol 277 (6) ◽

pp. L1109-L1117 ◽

Cited By ~ 22

Author(s):

Simon Johnson ◽

Alan Knox

Keyword(s):

Smooth Muscle ◽

Growth Factor ◽

Airway Smooth Muscle ◽

Fetal Bovine Serum ◽

Platelet Derived Growth Factor ◽

Airway Smooth Muscle Cells ◽

Human Airway Smooth Muscle ◽

Human Airway ◽

Smooth Muscle Proliferation ◽

Fetal Bovine

Airway smooth muscle proliferation is important in asthma and is dependent on pro- and antimitogenic factors and cell-matrix interactions. Here we show an antiproliferative effect of protease inhibitors on human airway smooth muscle due to inhibition of autocrine-derived matrix metalloproteinase (MMP)-2. Proliferation in response to fetal bovine serum, thrombin, and platelet-derived growth factor was inhibited by the broad-spectrum protease inhibitor Complete and the MMP inhibitors EDTA and Ro-31-9790 but not by cysteine or serine protease inhibitors. Conditioned medium from airway smooth muscle cells contained 72-kDa gelatinase that was secreted by growth-arrested cells and increased by fetal bovine serum but not by thrombin or platelet-derived growth factor. Immunostaining of cultured human airway smooth muscle cells and normal lung biopsies confirmed this gelatinase to be MMP-2. Our results suggest a novel role for MMP-2 as an important autocrine factor required for airway smooth muscle proliferation. Inhibition of MMPs could provide a target for the prevention of smooth muscle hyperplasia and airway remodeling in asthma.

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Friction in airway smooth muscle: mechanism, latch, and implications in asthma

Journal of Applied Physiology ◽

10.1152/jappl.1996.81.6.2703 ◽

1996 ◽

Vol 81 (6) ◽

pp. 2703-2703 ◽

Cited By ~ 168

Author(s):

J. J. Fredberg ◽

K. A. Jones ◽

M. Nathan ◽

S. Raboudi ◽

Y. S. Prakash ◽

...

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Time Course ◽

Molecular Mechanisms ◽

Mechanical Energy ◽

Frictional Stress ◽

Turnover Rates ◽

Shortening Velocity ◽

Biphasic Pattern ◽

Cross Bridge

Fredberg, J. J., K. A. Jones, M. Nathan, S. Raboudi, Y. S. Prakash, S. A. Shore, J. P. Butler, and G. C. Sieck. Friction in airway smooth muscle: mechanism, latch, and implications in asthma. J. Appl. Physiol. 81(6): 2703–2712, 1996.—In muscle, active force and stiffness reflect numbers of actin-myosin interactions and shortening velocity reflects their turnover rates, but the molecular basis of mechanical friction is somewhat less clear. To better characterize molecular mechanisms that govern mechanical friction, we measured the rate of mechanical energy dissipation and the rate of actomyosin ATP utilization simultaneously in activated canine airway smooth muscle subjected to small periodic stretches as occur in breathing. The amplitude of the frictional stress is proportional to ηE, where E is the tissue stiffness defined by the slope of the resulting force vs. displacement loop and η is the hysteresivity defined by the fatness of that loop. From contractile stimulus onset, the time course of frictional stress amplitude followed a biphasic pattern that tracked that of the rate of actomyosin ATP consumption. The time course of hysteresivity, however, followed a different biphasic pattern that tracked that of shortening velocity. Taken together with an analysis of mechanical energy storage and dissipation in the cross-bridge cycle, these results indicate, first, that like shortening velocity and the rate of actomyosin ATP utilization, mechanical friction in airway smooth muscle is also governed by the rate of cross-bridge cycling; second, that changes in cycling rate associated with conversion of rapidly cycling cross bridges to slowly cycling latch bridges can be assessed from changes of hysteresivity of the force vs. displacement loop; and third, that steady-state force maintenance (latch) is a low-friction contractile state. This last finding may account for the unique inability of asthmatic patients to reverse spontaneous airways obstruction with a deep inspiration.

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