TY - JOUR
T1 - Alteration of cross-bridge kinetics by myosin light chain phosphorylation in rabbit skeletal muscle
T2 - Implications for regulation of actin-myosin interaction
AU - Sweeney, H. Lee
AU - Stull, James T.
PY - 1990
Y1 - 1990
N2 - Myosin light chain phosphorylation in permeable skeletal muscle fibers increases isometric force and the rate of force production at submaximal levels of calcium activation; myosin light chain phosphorylation may underlie the increased rate and extent of force production associated with isometric twitch potentiation in intact fibers. To understand the mechanism by which myosin light chain phosphorylation manifests these effects, we have measured isometric force, isometric stiffness, rate of isometric force redevelopment after isotonic shortening, and isometric ATPase activity in permeabilized rabbit psoas muscle fibers. These measurements were made in the presence and absence of myosin light chain phosphorylation over a range of calcium concentrations that caused various levels of activation. The results were analyzed with a two-state cross-bridge cycle model as suggested by Brenner [Brenner, B. (1988) Proc. Natl. Acad. Sci. USA 85, 3265-3269]. The results indicate that myosin light chain phosphorylation exerts its effect on force generation and the isometric rate of force redevelopment in striated muscle through a single mechanism, namely, by increasing the rate constant describing the transition from non-force-generating crossbridges to force-generating states (fapp). gapp, the reverse rate constant, is unaffected by phosphorylation as are the number of cycling cross-bridges. Since both calcium and myosin light chain phosphorylation increase fapp, the possibility is considered that modulation of fapp may represent a general mechanism for regulating force in actin-myosin systems.
AB - Myosin light chain phosphorylation in permeable skeletal muscle fibers increases isometric force and the rate of force production at submaximal levels of calcium activation; myosin light chain phosphorylation may underlie the increased rate and extent of force production associated with isometric twitch potentiation in intact fibers. To understand the mechanism by which myosin light chain phosphorylation manifests these effects, we have measured isometric force, isometric stiffness, rate of isometric force redevelopment after isotonic shortening, and isometric ATPase activity in permeabilized rabbit psoas muscle fibers. These measurements were made in the presence and absence of myosin light chain phosphorylation over a range of calcium concentrations that caused various levels of activation. The results were analyzed with a two-state cross-bridge cycle model as suggested by Brenner [Brenner, B. (1988) Proc. Natl. Acad. Sci. USA 85, 3265-3269]. The results indicate that myosin light chain phosphorylation exerts its effect on force generation and the isometric rate of force redevelopment in striated muscle through a single mechanism, namely, by increasing the rate constant describing the transition from non-force-generating crossbridges to force-generating states (fapp). gapp, the reverse rate constant, is unaffected by phosphorylation as are the number of cycling cross-bridges. Since both calcium and myosin light chain phosphorylation increase fapp, the possibility is considered that modulation of fapp may represent a general mechanism for regulating force in actin-myosin systems.
KW - Contraction
KW - Modulation of force
UR - http://www.scopus.com/inward/record.url?scp=0025061076&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0025061076&partnerID=8YFLogxK
U2 - 10.1073/pnas.87.1.414
DO - 10.1073/pnas.87.1.414
M3 - Article
C2 - 2136951
AN - SCOPUS:0025061076
SN - 0027-8424
VL - 87
SP - 414
EP - 418
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 1
ER -