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.
Section of Pulmonary and Critical Care Medicine, Univ. of Chicago, MC6026, 5841 S. Maryland Ave., Chicago, IL 60637, USA.
M L
ML
Dowell
O J
OJ
Lakser
W T
WT
Gerthoffer
J J
JJ
Fredberg
G L
GL
Stelmack
A J
AJ
Halayko
J
J
Solway
R W
RW
Mitchell
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