Maximal stimulation-induced in situ myosin light chain kinase activity is upregulated in fetal compared with adult ovine carotid arteries

• Published in: American journal of physiology. Heart and circulatory physiology 2008-12, Vol.295 (6), p.H2289-H2298
• Main Authors: Injeti, Elisha R, Sandoval, Renan J, Williams, James M, Smolensky, Alexander V, Ford, Lincoln E, Pearce, William J
• Format: Article
• Language: English
• Subjects: Age Factors; Aging - metabolism; Animals; Azepines - pharmacology; Biochemistry; Calcium; Calmodulin - metabolism; Carotid Artery, Common - embryology; Carotid Artery, Common - enzymology; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Enzymes; Fetus - blood supply; Fetuses; Kinases; Myosin Light Chains - metabolism; Myosin-Light-Chain Kinase - antagonists & inhibitors; Myosin-Light-Chain Kinase - metabolism; Myosin-Light-Chain Phosphatase - antagonists & inhibitors; Myosin-Light-Chain Phosphatase - metabolism; Naphthalenes - pharmacology; Oxazoles - pharmacology; Phosphorylation; Sheep; Time Factors; Up-Regulation; Vasoconstriction; Veins & arteries
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00606.2008

1 Divisions of Physiology and Pharmacology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California; and 2 Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana Submitted 9 June 2008 ; accepted in final form 1 October 2008 Postnatal decreases in vascular reactivity involve decreases in the thick filament component of myofilament calcium sensitivity, which is measured as the relationship between cytosolic calcium concentration and myosin light chain (MLC 20 ) phosphorylation. The present study tests the hypothesis that downregulation of thick filament reactivity is due to downregulation of myosin light chain kinase (MLCK) activity in adult compared with fetal arteries. Total MLCK activity, calculated as %MLC 20 phosphorylated per second in intact arteries during optimal inhibition of myosin light chain phosphatase activity, was significantly less in adult (6.56 ± 0.29%) than in fetal preparations (7.39 ± 0.53%). In situ MLC 20 concentrations (µM) in adult (198 ± 28) and fetal arteries (236 ± 44) did not differ significantly. In situ MLCK concentrations (µM), however, were significantly greater in adult (8.21 ± 0.59) than in fetal arteries (1.83 ± 0.13). In situ MLCK activities (ng MLC 20 phosphorylated·s –1 ·ng MLCK –1 ) were significantly less in adult (0.26 ± 0.01) than in fetal arteries (1.52 ± 0.11). In contrast, MLCK activities in adult (15.8 ± 1.5) and fetal artery homogenates (17.3 ± 1.3) were not significantly different. When in situ fractional activation was calculated, adult values (1.72 ± 0.17%) were significantly less than fetal values (9.08 ± 0.83%). Together, these results indicate that decreased thick filament reactivity in adult compared with fetal ovine carotid arteries is due at least in part to greater MLCK activity in fetal arteries, which in turn cannot be explained by differences in MLCK, MLC 20 , or calmodulin concentrations. Instead, this difference appears to involve age-related differences in fractional activation of the MLCK enzyme. myofilament calcium sensitivity; postnatal maturation; regulatory myosin light chain; thick filament reactivity Address for reprint requests and other correspondence: W. J. Pearce, Center for Perinatal Biology, Loma Linda Univ. School of Medicine, Loma Linda, CA 92354 (e-mail: wpearce{at}llu.edu )