Temporal relationship between force, ATPase activity, and myosin phosphorylation during a contraction/relaxation cycle in a skinned smooth muscle

1990 ◽  
Vol 416 (5) ◽  
pp. 512-518 ◽  
Author(s):  
H. K�hn ◽  
A. Tewes ◽  
M. Gagelmann ◽  
K. G�th ◽  
A. Arner ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Atpase Activity ◽  
Temporal Relationship ◽  
Relaxation Cycle ◽  
Myosin Phosphorylation ◽  
Skinned Smooth Muscle

Role of magnesium in activation of smooth muscle

1988 ◽  
Vol 255 (4) ◽  
pp. C465-C472 ◽  
Author(s):  
R. J. Paul ◽  
J. C. Ruegg
Keyword(s):  
Smooth Muscle ◽  
Regulatory Mechanism ◽  
Isometric Force ◽  
Taenia Coli ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Skinned Smooth Muscle ◽  
Myosin Interaction ◽  
Gamma S

We studied the effects of Mg2+-free solutions on isometric force (F0) and unloaded shortening velocity (Vus) in contractions elicited by Ca2+ or by ATP after thiophosphorylation by adenosine 5'-O-(3-thiotriphosphate (ATP gamma S) in chemically skinned guinea pig taenia coli smooth muscle. In Mg2+-free solutions, increasing Ca2+ did not increase Fo above resting levels. At the peak of a control contraction elicited by Ca2+, transfer to Mg2+-free (but Ca2+-containing) solutions resulted in a rapid relaxation and concomitant dephosphorylation of myosin. After ATP gamma S, a contracture required neither Mg2+ nor Ca2+ in the solutions for control levels of Fo. Vus in the Mg2+-free solutions after ATP gamma S was approximately 50% of control and could be restored to near control levels by addition of Mg2+ but not Ca2+. After ATP gamma S, pretreatment with 4 mM EDTA and contracture in 0.1 mM EDTA-containing solutions decreased Fo to 70-80% of control and Vus to 50-60% of control. Our results suggest that the relatively high requirement for Mg2+ for contraction in skinned smooth muscle largely reflects the Mg2+ dependence of myosin kinase and not for actin-myosin interaction. The dependence of Fo on Mg2+ (in the presence of excess ATP) in taenia coli is less than that reported for skeletal muscle. Appreciable force can be maintained with no added Mg2+ in the presence of 4 mMEDTA, and thus it appears that ATP4- can be a substrate for contraction after ATP gamma S treatment. In addition, our data imply that any Ca2+-dependent regulatory mechanism that does not involve myosin phosphorylation/dephosphorylation, if present, requires Mg2+ for expression.

An expanded latch-bridge model of protein kinase C-mediated smooth muscle contraction

2005 ◽  
Vol 98 (4) ◽  
pp. 1356-1365 ◽  
Author(s):  
Chi-Ming Hai ◽  
Hak Rim Kim
Keyword(s):  
Smooth Muscle ◽  
Atpase Activity ◽  
Thin Filament ◽  
Muscle Mechanics ◽  
Smooth Muscle Contraction ◽  
Myosin Phosphorylation ◽  
Cross Bridge ◽  
Bridge Model ◽  
Cross Bridges ◽  
Smooth Muscle Mechanics

A thin-filament-regulated latch-bridge model of smooth muscle contraction is proposed to integrate thin-filament-based inhibition of actomyosin ATPase activity with myosin phosphorylation in the regulation of smooth muscle mechanics. The model included two latch-bridge cycles, one of which was identical to the four-state model as proposed by Hai and Murphy ( Am J Physiol Cell Physiol 255: C86–C94, 1988), whereas the ultraslow cross-bridge cycle has lower cross-bridge cycling rates. The model-fitted phorbol ester induced slow contractions at constant myosin phosphorylation and predicted steeper dependence of force on myosin phosphorylation in phorbol ester-stimulated smooth muscle. By shifting cross bridges between the two latch-bridge cycles, the model predicts that a smooth muscle cell can either maintain force at extremely low-energy cost or change its contractile state rapidly, if necessary. Depending on the fraction of cross bridges engaged in the ultraslow latch-bridge cycle, the model predicted biphasic kinetics of smooth muscle mechanics and variable steady-state dependencies of force and shortening velocity on myosin phosphorylation. These results suggest that thin-filament-based regulatory proteins may function as tuners of actomyosin ATPase activity, thus allowing a smooth muscle cell to have two discrete cross-bridge cycles with different cross-bridge cycling rates.

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