Abstract

The study examines the hypothesis that maturation changes the ability of cGMP to produce cerebral vasodilatation and alters the relative intracellular calcium pool sizes in ovine arteries. In ovine basilars taken from near-term fetal and young adult sheep, 8- pCPT-cGMP relaxed potassium- and serotonin-induced tone with pD2 values of 4.4±0.1 and 4.9±0.1 (fetal basilar) and 4.0±0.1 and 4.7±0.1 (adult basilar), respectively. In fura-2 loaded arteries, 8-pCPT-cGMP significantly lowered increases in cytosolic calcium concentration induced by serotonin but not potassium regardless of age. When calcium sensitivity was calculated in the same arteries as the slope of the relation between calcium concentration and contractile tension, 8-pCPT-cGMP lowered calcium sensitivity in both adult and fetal potassium-contracted arteries. In serotonin-contracted arteries, however, 8-pCPT-cGMP lowered calcium sensitivity only in fetal but not in adult arteries. In - toxin and -escin permeabilized arteries, pD2 values for calcium-, GTP S-, and 5HT-induced tone were shifted to the right following treatment of 8-pCPT-cGMP.

This study identifies four definable functional calcium pools within cerebrovascular smooth muscle that include pools releasable by: 1) both ins(1,4,5)P3 and ryanodine; 2) ins(1,4,5)P3 but not ryanodine; 3) ryanodine but not ins(1,4,5)P3; and 4) neither ins(1,4,5)P3 nor ryanodine, but releasable by calcium ionophore (A23187). The pool sensitive to both ryanodine and ins(1,4,5)P3 was quite small in both fetal (6%) and adult (5%) arteries, suggesting that ryanodine and ins(1,4,5)P3 pools were reasonably distinct in our preparation. The pool sensitive to ins(1,4,5)P3 alone was dramatically larger in adult (59%) than in fetal (13%) arteries. The pool sensitive to ryanodine alone was small in fetal (9%) and even smaller in adult (4%) arteries. The pool sensitive to neither ins(1,4,5)P3 nor ryanodine were markedly greater in fetal (72%) than in adult (32%) arteries.

Together, these results demonstrate that 1) cGMP attenuates cytosolic calcium concentration more than its effect on myofilament calcium sensitivity; 2) both potassium-induced and 5HT-induced contractions were more sensitive to cGMP in fetal than adult arteries; 3) cGMP had no effects on potassium-induced increases in cytosolic calcium, however, 5HT-evoked increases were sensitive to the attenuating effects of cGMP: fetal arteries being more sensitive than adult basilars; 4) cGMP attenuated both basal and agonist-enhanced myofilament calcium sensitivity.

The present study also demonstrates that during enlargement of vascular smooth muscle cells typical of maturation, much of the increased intracellular volume becomes dedicated to expansion of ins(1,4,5)P3-sensitive calcium stores. These data further suggest that postnatal changes in cerebrovascular calcium metabolism involve major redistributions of intracellular calcium with important consequences for the mechanisms whereby contractions are initiated and maintained. Overall, these data further propose that the mechanisms of cGMP-induced decreases in cytosolic calcium may be markedly different during maturation due to re-organization of calcium buffering system during sarcoplasmic reticulum development.

LLU Discipline

Pharmacology

Department

Pharmacology

School

Graduate School

First Advisor

William J. Pearce

Second Advisor

John N. Buchholz

Third Advisor

William T. Gerthoffer

Fourth Advisor

J. Mailen Kootsey

Fifth Advisor

Lubo Zhang

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

2001

Date (Title Page)

6-2001

Language

English

Library of Congress/MESH Subject Headings

Aging; Cyclic GMP -- pharmacology; Vasodilation -- physiology; Cerebrovascular Circulation -- physiology; Artery -- physiology

Type

Dissertation

Page Count

xiii; 180

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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