Maturational Changes in Myosin Light Chain Kinase Activity in Ovine Carotids

Date of Award

9-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Institution Granting Degree

Loma Linda University

Cedarville University School or Department

Pharmaceutical Sciences

First Advisor

William J. Pearce

Second Advisor

John N. Buckholz

Third Advisor

Surya M. Nauli

Keywords

Vascular reactivity, myosin, ateries, ovine carotid

Abstract

Vascular reactivity changes dramatically during postnatal maturation due in large part to developmental changes in myofilament calcium sensitivity. Recent findings suggest that reactivity of the thick filament component of calcium sensitivity is upregulated in fetal compared to adult arteries. In light of these findings, the present study tests the hypothesis that upregulation of fetal thick filament reactivity is due to upregulation of myosin light chain kinase (MLCK) activity. To test this hypothesis, MLCK abundance and its activity is measured in intact arteries. The results indicate that MLCK abundance is 6.03 ± 0.96 fold greater in adult than in fetal arteries. Total MLCK activity (%MLC phosphorylated/sec) estimated as the rate of phosphorylation of myosin light chain in intact arteries was greater in fetal (7.39 ± 0.53) than in adult (6.56 ± 0.29) arteries. When total MLCK activity was normalized relative to MLCK & MLC abundance to estimate the apparent specific activity of MLCK (ng MLC phosphorylation/sec/ng MLCK), these estimates were dramatically greater in fetal (1.52 ± 1.11) than in adult (0.26 ± 0.01) arteries.

Further, to test if these differences are due to differences in fractional activation of the enzyme, maximum velocity (Vmax) of MLCK was estimated in artery homogenates. The results indicate that Vmax (ng MLC phosphorylated/sec) is significantly greater in fetal (163 ± 11) compared to adult (130 ± 9) arteries. When fractional activation was calculated the results showed about 4.9 ± 0.3 fold greater activation of MLCK in fetal compared to adult arteries.

Together, these results support the hypothesis that upregulation of fetal thick filament reactivity is due to upregulation of MLCK activity. These studies were the first to offer a quantitative assessment of age related differences in MLCK activity in intact arteries and indicate the relative extents to which changes in MLCK abundance, activity and fractional activation contribute to these differences. From a clinical science perspective, these studies help in understanding the mechanisms involved in adaptation of fetal vascular system for postnatal life so that, new strategies of pharmacological management of NICU neonates with cerebrovascular and cardiovascular instabilities can be developed.

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