Regulation of contraction kinetics in skinned skeletal muscle fibers by calcium and troponin C.
The influences of [Ca(2+)] and Ca(2+) dissociation rate from troponin C (TnC) on the kinetics of contraction (k(Ca)) activated by photolysis of a caged Ca(2+) compound in skinned fast-twitch psoas and slow-twitch soleus fibers from rabbits were investigated at 15 degrees C. Increasing the amount of Ca(2+) released increased the amount of force in psoas and soleus fibers and increased k(Ca) in a curvilinear manner in psoas fibers approximately 5-fold but did not alter k(Ca) in soleus fibers. Reconstituting psoas fibers with mutants of TnC that in solution exhibited increased Ca(2+) affinity and approximately 2- to 5-fold decreased Ca(2+) dissociation rate (M82Q TnC) or decreased Ca(2+) affinity and approximately 2-fold increased Ca(2+) dissociation rate (NHdel TnC) did not affect maximal k(Ca). Thus the influence of [Ca(2+)] on k(Ca) is fiber type dependent and the maximum k(Ca) in psoas fibers is dominated by kinetics of cross-bridge cycling over kinetics of Ca(2+) exchange with TnC.
Luo
Ye
Y
Department of Physiology and Cell Biology, Ohio State University, 1645 Neil Ave, Columbus, OH 43210-1218, USA.
Rall
Jack A
JA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D007537:Isometric Contraction / Q000502:physiology*; D007700:Kinetics; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011817:Rabbits; D013314:Stress, Mechanical; D019209:Troponin C / Q000378:metabolism*
D019209:Troponin C; D002118:Calcium