Latrunculin B increases force fluctuation-induced relengthening of ACh-contracted, isotonically shortened canine tracheal smooth muscle.
We hypothesized that differences in actin filament length could influence force fluctuation-induced relengthening (FFIR) of contracted airway smooth muscle and tested this hypothesis as follows. One-hundred micromolar ACh-stimulated canine tracheal smooth muscle (TSM) strips set at optimal reference length (Lref) were allowed to shorten against 32% maximal isometric force (Fmax) steady preload, after which force oscillations of +/-16% Fmax were superimposed. Strips relengthened during force oscillations. We measured hysteresivity and calculated FFIR as the difference between muscle length before and after 20-min imposed force oscillations. Strips were relaxed by ACh removal and treated for 1 h with 30 nM latrunculin B (sequesters G-actin and promotes depolymerization) or 500 nM jasplakinolide (stabilizes actin filaments and opposes depolymerization). A second isotonic contraction protocol was then performed; FFIR and hysteresivity were again measured. Latrunculin B increased FFIR by 92.2 +/- 27.6% Lref and hysteresivity by 31.8 +/- 13.5% vs. pretreatment values. In contrast, jasplakinolide had little influence on relengthening by itself; neither FFIR nor hysteresivity was significantly affected. However, when jasplakinolide-treated tissues were then incubated with latrunculin B in the continued presence of jasplakinolide for 1 more h and a third contraction protocol performed, latrunculin B no longer substantially enhanced TSM relengthening. In TSM treated with latrunculin B + jasplakinolide, FFIR increased by only 3.03 +/- 5.2% Lref and hysteresivity by 4.14 +/- 4.9% compared with its first (pre-jasplakinolide or latrunculin B) value. These results suggest that actin filament length, in part, determines the relengthening of contracted airway smooth muscle.
Dowell
M L
ML
Section of Pulmonary and Critical Care Medicine, Univ. of Chicago, MC6026, 5841 S. Maryland Ave., Chicago, IL 60637, USA.
Lakser
O J
OJ
Gerthoffer
W T
WT
Fredberg
J J
JJ
Stelmack
G L
GL
Halayko
A J
AJ
Solway
J
J
Mitchell
R W
RW
D000109:Acetylcholine / Q000494:pharmacology*; D008841:Actin Cytoskeleton / Q000502:physiology*; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology*; D047630:Depsipeptides / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D013314:Stress, Mechanical; D013844:Thiazoles / Q000494:pharmacology*; D053778:Thiazolidines; D014132:Trachea / Q000187:drug effects / Q000502:physiology*
D019086:Bridged Bicyclo Compounds, Heterocyclic; D047630:Depsipeptides; D013844:Thiazoles; D053778:Thiazolidines; C057531:jasplakinolide; C037068:latrunculin B; D000109:Acetylcholine