Differential expression and effect of 1,25 (oh)2 vitamin d3 on
myosin in the arterial tree of rats.
Ishibashi, Katsuhiko, Adam Evans, Tetsuji Shingu, Ka Bian, and Richard
D. Bukoski.
Hypertension and Vascular Research Laboratories, Departments of
Internal Medicine and Physiology and Biophysics, University of Texas
Medical Branch, Galveston Island, Texas 77555
APStracts 2:0098C, 1995.
The hypothesis that 1,25 (OH)2 vitamin D3 (1,25 vitD, calcitriol)
modulates myosin expression in vascular smooth muscle was tested.
Wistar Kyoto or spontaneously hypertensive rats given intraperitoneal
injections of 25 ng 1,25 vitD/100g body weight for varying periods of
time showed a greater than 2-fold increase in aortic mRNA encoding
the myosin regulatory light chain relative to 18S rRNA (p<0.05). 1,25
vitD administration to Wistar rats caused a significant increase in
the aortic content of total myosin regulatory light chain and total
myosin heavy chain. The increase in myosin light chain was the result
of a specific increase in expression of its smooth muscle isoform
(control=65.2+3.4% vs 1,25 vitD=78.7+3.6%, p=0.020). 1,25 vitD had no
effect on total myosin light chain or heavy chain in the superior
mesenteric artery. The hormone did, however, increase the proportion
of the smooth muscle isoform of the light chain in this vessel
(control=81.4+2.6% vs 1,25 vitD=88.8+2.1%, p=0.048). In branch II and
III mesenteric resistance arteries, 1,25 vitD significantly increased
the active stress response to 10 [mu]mol/L norepinephrine, but was
without effect on total myosin light chain or heavy chain content or
on the relative expression of the myosin light chain isoforms
(control=94.0 +1.4% vs 1,25 vitD=95.8+1.1%, p=0.33). We conclude that
(a) 1,25 vitD enhances expression of myosin light chain and heavy
chain in the aorta but not the more muscular mesenteric arteries, (b)
the increase in light chain is the result of an increase in the
smooth muscle isoform of the protein raising the possibility that
1,25 vitD exerts a differentiating effect in the aorta, (c) there is
differential distribution and calcitriol responsiveness of the smooth
muscle isoform of the light chain along the arterial tree, and (d)
1,25 vitD enhances stress generation in the resistance artery by an
effect that is independent of its pro-myosin activity.
Received 11 October 1994; accepted in final form 6 February 1995.
APS Manuscript Number C606-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.