Postnatal maturation increases the abundance, but decreases the specific activity, of MLCK in ovine carotids

Abstract

The regulation of myofilament Ca ++ sensitivity changes with postnatal age, such that the ability of increases in cytosolic Ca ++ to stimulate myosin light chain phosphorylation is upregulated in fetal compared to adult carotid arteries. Although considerable attention has been paid to the role of myosin light chain phosphatase in this regulation, the present study tests the hypothesis that age‐related differences in thick‐filament regulation also involve changes in myosin light chain kinase (MLCK) activity. Western blot analysis revealed that MLCK abundance was 16±1 times greater in adult than in fetal arteries. To measure MLCK activity in situ, arteries were incubated in the presence of 30 nM Calyculin A to inhibit phosphatase activity, then were frozen at 0,4,8, and 12 seconds of exposure to 120 mM K + , and analyzed for MLC phosphorylation using urea/glycerol gels. MLCK activity was estimated as the rate of change in phosphorylation, and was significantly greater in fetal (27±4 %/sec) than in adult (19±2 %/sec) arteries. Together, these results demonstrate that MLCK abundance and specific activity are inversely related during postnatal maturation, and that changes in MLCK activity contribute significantly to age‐related differences in thick‐filament regulation in ovine carotid arteries. Supported by NIH HD31226, HL54120, and HL64867.