Key Points
- To evaluate the effect of myosin light chain phosphorylation on isometric tension generation during submaximal calcium activation in permeabilized mammalian cardiac and skeletal muscle cells.
- Permeabilized rabbit psoas (skeletal) and ventricular (cardiac) muscle fibers were activated across ranges of calcium concentrations (pCa 6.0–5.4 for skeletal; pCa 6.2–5.6 for cardiac).
- Fibers were incubated with 0.15 µM myosin light chain kinase and 2 µM calmodulin at pCa 5.4 to increase light chain phosphorylation from 5–10% to 60–75%.
- Isometric tension generation across the specified pCa activation sequences was re-measured after 5 minutes of phosphorylation treatment.
- Phosphorylation of the regulatory P-light chain increased tension development in both permeabilized skeletal and cardiac muscle fibers at submaximal calcium levels (<50% maximal activation).
- Phosphorylation induced a leftward shift in the pCa-tension relationship accompanied by a decrease in the slope of the activation curve, demonstrating increased calcium sensitivity.
Structured PICO
PPopulationPermeabilized rabbit psoas and ventricular muscle fibers
IInterventionAddition of myosin light chain kinase (0.15 microM) and calmodulin (2 microM) to induce myosin light chain phosphorylation
CComparatorBaseline tension production before phosphorylation
OOutcomeTension production at submaximal Ca2+ activation levels (pCa-tension relationship)surrogate
Myosin light chain phosphorylation enhances actin-myosin interactions and increases tension production at submaximal calcium levels in mammalian cardiac and skeletal muscle.