Nebulin plays a direct role in promoting strong actin-myosin interactions.
The role of the actin filament-associated protein nebulin on mechanical and kinetic properties of the actomyosin motor was investigated in skeletal muscle of wild-type (wt) and nebulin-deficient (nebulin(-)(/)(-)) mice that were 1 d old, an age at which sarcomeric structure is still well preserved. In Ca2+-activated skinned fibers from psoas muscle, we determined the Ca2+ dependence of isometric force and stiffness, the rate of force redevelopment after unloaded shortening (k(TR)), the power during isotonic shortening, and the unloaded shortening velocity (V(0)). Our results show a 65% reduction in isometric force in nebulin(-)(/)(-) fibers at saturating [Ca2+], whereas neither thin-filament length nor the Ca2+ sensitivity of the contractile system is affected. Stiffness measurements indicate that the reduction in isometric force is due to a reduction in the number of actin-attached myosin motors, whereas the force of the motor is unchanged. Furthermore, in nebulin(-)(/)(-) fibers, k(TR) is decreased by 57%, V(0) is increased by 63%, and the maximum power is decreased by 80%. These results indicate that, in the absence of nebulin, the attachment probability of the myosin motors to actin is decreased, revealing a direct role for nebulin in promoting strong actomyosin interactions responsible for force and power production.
Bang
Marie-Louise
ML
Istituto Tecnologie Biomediche-Consiglio Nazionale delle Ricerche (ITB-CNR), Via Fratelli Cervi 93, 20090 Segrate, Milan, Italy. m.bang@itb.cnr.it
Caremani
Marco
M
Brunello
Elisabetta
E
Littlefield
Ryan
R
Lieber
Richard L
RL
Chen
Ju
J
Lombardi
Vincenzo
V
Linari
Marco
M
D000199:Actins / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology; D009218:Myosins / Q000378:metabolism*
D000199:Actins; D009124:Muscle Proteins; C035620:nebulin; D009218:Myosins; D002118:Calcium
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