Regulatory light chain phosphorylation increases eccentric contraction–induced injury in skinned fast‐twitch fibers

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Abstract
During contraction, activation of Ca2+/calmodulin–dependent myosin light chain kinase (MLCK) results in phosphorylation of myosin's regulatory light chain (RLC), which potentiates force and increases speed of force development over a wide range of [Ca2+]. We tested the hypothesis that RLC phosphorylation by MLCK mediates the extent of eccentric contraction–induced injury as measured by force deficit in skinned fast‐twitch skeletal muscle fibers. Results indicated that RLC phosphorylation in single skinned rat psoas fibers significantly increased Ca2+ sensitivity of isometric force; isometric force from 50 ± 16 to 59 ± 18 kN/m2 during maximal Ca2+ activation; peak absolute power output from 38 ± 15 to 48 ± 14 nW during maximal Ca2+ activation; and the magnitude of contraction‐induced force deficit during maximal (pCa 4.5) activation from 26 ± 9.8 to 35 ± 9.6%. We conclude that RLC phosphorylation increases force deficits following eccentric contractions, perhaps by increasing the number of force‐generating cross‐bridges. Muscle Nerve 29: 313–317, 2004
Funding Information
  • Muscular Dystrophy Association

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