Physiological variations in ovine cerebrovascular calcium
sensitivity.
Akopov, Sergey E., Lubo Zhang, and William J. Pearce.
Departments of Physiology, Pharmacology, and Biochemistry, Center
for Perinatal Biology, Loma Linda University School of Medicine, Loma
Linda, California, 92350
APStracts 3:0542H, 1996.
Cerebrovascular reactivity to biogenic amines varies in relation to
both artery diameter and age. The present study examines the
hypothesis that these patterns of reactivity are secondary to
corresponding variations in the Ca2+ sensitivity of the contractile
proteins. To test this hypothesis, we permeabilized segments of
common carotid (COM), basilar (BAS), main branch middle cerebral
(MCA), and second branch middle cerebral (MCA-B) arteries from non
-pregnant adult and near-term fetal sheep using -escin.
Permeabilization methods were carefully validated and adjusted for
each artery type. Baseline myofilament Ca2+ sensitivity in both
adults and fetuses increased significantly from COM to MCA-B, and was
generally higher in fetuses than adults. Serotonin dose-dependently
increased Ca2+ sensitivity via a G-protein dependent mechanism in all
arteries. The magnitudes of this effect did not vary among artery
types but were significantly greater in fetal than adult arteries.
This effect of 5HT was mimicked by GTPgS, a nonhydrolyzable analog of
GTP, and its effects were also much greater in fetal than adult
arteries. We conclude that patterns of cerebrovascular reactivity to
biogenic amines are determined, at least in part, by underlying
variations in baseline myofilament Ca2+ sensitivity and/or its
alteration by G-protein dependent mechanisms.
Received 27 September 1996; accepted in final form 6 December
1996.
APS Manuscript Number H874-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996