Exogenous calmodulin increases Ca2+ sensitivity of isometric tension activation and myosin phosphorylation in skinned smooth muscle

1981 ◽  
Vol 392 (2) ◽  
pp. 115-120 ◽  
Author(s):  
P. S. Cassidy ◽  
W. G. L. Kerrick ◽  
P. E. Hoar ◽  
D. A. Malencik
Keyword(s):  
Smooth Muscle ◽  
Isometric Tension ◽  
Myosin Phosphorylation ◽  
Skinned Smooth Muscle

Effects of Ca2+, Mg2+, and myosin phosphorylation on skinned smooth muscle fibers

1987 ◽  
Vol 252 (5) ◽  
pp. C543-C554 ◽  
Author(s):  
R. J. Barsotti ◽  
M. Ikebe ◽  
D. J. Hartshorne
Keyword(s):  
Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Isometric Tension ◽  
Skinned Fibers ◽  
Myosin Light Chain Phosphorylation ◽  
Shortening Velocity ◽  
Myosin Phosphorylation ◽  
Chicken Gizzard ◽  
Skinned Smooth Muscle

Isometric tension, unloaded shortening velocity (Vus), and myosin light chain phosphorylation were measured with skinned chicken gizzard fibers at various Ca2+ concentrations and at two concentrations of free Mg2+, 0.7 and 2.2 mM. At low free Mg2+, an increase in Ca2+ from pCa 8.0 to 6.4 resulted in an increase of all three parameters. Between pCa 6.4 and 5.0, isometric tension and phosphorylation remained constant but Vus continued to increase. At low free Mg2+, therefore, Vus showed a dependence both on phosphorylation and on Ca2+. At high free Mg2+, tension and Vus increased as phosphorylation increased and both were maximum at pCa 6.4, where phosphorylation became constant. Therefore, at high free Mg2+, Vus was dependent only on phosphorylation and did not show an additional Ca2+ dependence. Incubation of the Ca2+-independent kinase (approximately 3 microM) with skinned fibers under various conditions resulted in a constant level of phosphorylation (49-58%). At high free Mg2+ plus the Ca2+-independent kinase Vus was independent of Ca2+, whereas at low free Mg2+ Vus increased from pCa 6.4 to 5.0. These data are consistent with the hypothesis that Ca2+ binding to the Ca2+-Mg2+ sites of myosin increase Vus and that this occurs at Ca2+ concentrations higher than those necessary to saturate calmodulin.

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.

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