Maturation Depresses cGMP-Mediated Decreases in [Ca2+]i and Ca2+ Sensitivity in Ovine Cranial Arteries

Document Type

Article

Publication Date

3-2001

Abstract

Because cerebrovascular cGMP levels vary significantly during maturation, we examined the hypothesis that the ability of cGMP to relax cerebral arteries also changes during maturation. In concentration-response experiments, potassium-induced tone in basilar arteries was significantly more sensitive to a nonmetabolizable cell-permeant cGMP analogue 8-(p-chlorophenylthio)-cGMP (8-pCPT-cGMP) in term fetal [-log one-half maximal concentration (EC50) = 4.4 +/- 0.1 M] than in adult (-log EC50 = 4.0 +/- 0.1 M) ovine basilar arteries. Serotonin-induced tone also revealed significantly greater sensitivity to the cGMP analogue in fetal (-log EC50 = 4.9 +/- 0.1 M) than in adult (-log EC50 = 4.7 +/- 0.1 M) basilars. In fura 2-loaded preparations, 8-pCPT-cGMP had no significant effect on cytosolic calcium concentrations in potassium-contracted arteries but at 6 muM significantly reduced calcium only in fetal basilars (Delta = 33 +/- 8%). Higher 8-pCPT-cGMP concentrations reduced cytosolic calcium in both fetal and adult basilars. Similarly, in both potassium- and 5-hydroxytryptamine (5-HT)-contracted preparations, low concentrations of 8-pCPT-cGMP reduced myofilament calcium sensitivity only in fetal basilars (Delta = 29 +/- 6 and Delta = 42 +/- 10%, respectively), whereas higher concentrations reduced calcium sensitivity in both fetal and adult arteries. In beta -escin-permeabilized arteries, equivalent reductions in basal and agonist-enhanced myofilament calcium sensitivity were produced by much lower 8-pCPT-cGMP concentrations in fetal (172 and 61 muM, respectively) than in adult (410 and 231 muM, respectively) basilars. The mechanisms mediating cGMP-induced vasorelaxation appear similar in fetal and adult arteries, with the exception that they are much more sensitive to cGMP in fetal than adult arteries. These age-related differences in the sensitivity of cytosolic calcium concentration, basal, and agonist-enhanced myofilament calcium sensitivity to cGMP can easily explain why both potassium- and 5-HT-induced tone are more sensitive to cGMP in fetal than adult cerebral arteries.

Comments

This article was originally published in American Journal of Physiology - Heart and Circulatory Physiology, volume 280, issue 3, in March 2001.

Copyright

American Physiological Society

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