ATP hydrolysis during contraction of permeabilized airway smooth muscle.
This study determined whether the time-dependent decline in the rate of ATP hydrolysis by actomyosin ATPase during sustained isometric force can occur in the absence of a time-dependent decline in regulatory myosin light chain (rMLC) phosphorylation in Triton X-100-permeabilized canine tracheal smooth muscle. Maximal activation with 10 microM Ca(2+) induced sustained increases in isometric force, stiffness, and rMLC phosphorylation; however, the increase in the ATP hydrolysis rate was initially high but then declined to a steady-state level above that of the unstimulated muscle (basal 31.8 +/- 5.8 nmol. cm(-3). s(-1); peak 81.4 +/- 11.3 nmol. cm(-3). s(-1); steady-state 62.2 +/- 9.1 nmol. cm(-3). s(-1)). Activation of strips in which the rMLC was irreversibly and maximally thiophosphorylated with adenosine 5'-O-(3-thiotriphosphate) also induced sustained increases in isometric force and stiffness but a nonsustained increase in ATP hydrolysis rate. There was no significant difference in the peak or steady-state isometric force, stiffness, or ATP hydrolysis rate or in the steady-state maximum unloaded shortening velocity between strips activated by 10 microM Ca(2+) or rMLC thiophosphorylation (0.058 +/- 0.016 and 0.047 +/- 0.011 muscle lengths/s, respectively). Mechanisms other than changes in rMLC phosphorylation contribute to the time-dependent decline in actomyosin ATPase activity during sustained activation of canine tracheal smooth muscle.
Jones
K A
KA
Departments of Anesthesiology and Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
Lorenz
R R
RR
Prakash
Y S
YS
Sieck
G C
GC
Warner
D O
DO
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D004548:Elasticity; D005260:Female; D006868:Hydrolysis; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D010539:Permeability; D010766:Phosphorylation; D013997:Time Factors; D014132:Trachea / Q000378:metabolism / Q000502:physiology*; D000077191:Wortmannin
D000730:Androstadienes; D018994:Myosin Light Chains; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D000077191:Wortmannin