Pharmaceutical Sciences Faculty Publications

Title

Maximal Stimulation-induced in Situ Myosin Light Chain Kinase Activity is Upregulated in Fetal Compared with Adult Ovine Carotid Arteries

Document Type

Article

Publication Date

12-1-2008

Journal Title

American Journal of Physiology - Heart and Circulatory Physiology

ISSN

0363-6135

Volume

295

Issue

6

First Page

2289

Last Page

2298

DOI

http://dx.doi.org/10.1152/ajpheart.00606.2008

PubMed ID

18835918

PubMed Central® ID

PMC2614542

Abstract

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 (MLC20) 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 %MLC20 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 MLC20 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 MLC20phosphorylated·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, MLC20, or calmodulin concentrations. Instead, this difference appears to involve age-related differences in fractional activation of the MLCK enzyme.

Keywords

Myofilament calcium sensitivity, postnatal maturation, regulatory myosin light chain, thick filament reactivity