F-actin disruption attenuates agonist-induced [Ca2+], myosin phosphorylation, and force in smooth muscle.
Cytochalasins B and D (at 10 microM) inhibited stress development induced by 1 microM carbachol in bovine tracheal smooth muscle by 55% and 90%, respectively. Glucose depletion was ineffective in inhibiting carbachol-induced contraction, indicating that inhibition of glucose transport was not the cause. Cytochalasin D-treated smooth muscle cells appeared collapsed, with spiky protrusions from the cell membrane. Deconvolution of fluorescent images of fluorescein isothiocyanate-phalloidin-labeled smooth muscle cells revealed concentrations of actin filaments near the cell periphery, including near the spiky protrusions. Cytochalasin B attenuated carbachol-induced intracellular Ca2+ concentration ([Ca2+]), especially the initial peak intracellular [Ca2+]. Cytochalasin B also attenuated carbachol-induced myosin light chain phosphorylation. However, when the myosin phosphorylation data were plotted against time-matched intracellular [Ca2+] data, the two relationships in control and cytochalasin B-treated smooth muscle were similar, suggesting that the changes in myosin phosphorylation could be explained by the changes in intracellular [Ca2+]. These results suggest that actin filaments in smooth muscle cells are dynamic and may be an integral component of Ca2+ regulation and/or signal transduction in receptor-coupled mechanisms.
Tseng
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S
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
Kim
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Kim
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Morgan
K G
KG
Hai
C M
CM
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D003571:Cytochalasin B / Q000494:pharmacology*; D015638:Cytochalasin D / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000502:physiology
D000199:Actins; D015638:Cytochalasin D; D003571:Cytochalasin B; D002217:Carbachol; D009218:Myosins; D011188:Potassium; D002118:Calcium