Maturation attenuates the effects of cGMP on contraction, [Ca2+]i and Ca2+ sensitivity in ovine basilar arteries.
The present study explores the hypothesis that age-related variations in cerebrovascular responses to vasodilators reflect corresponding age-dependent differences in the mechanisms coupling changes in cytosolic cGMP to vasorelaxation. The experiments focused on cGMP's ability to decrease either [Ca2+]i or myofilament Ca2+ sensitivity, because both effects can contribute to cGMP-induced vasodilation. Use of the cGMP analog 8-pCPT-cGMP minimized problems associated with limited cell permeation or cGMP hydrolysis. In fetal basilars contracted with 10 microM serotonin, the EC30 for 8-pCPT-cGMP-induced relaxation was 6 microM. In fura-2 loaded fetal basilars, pretreatment with 6 microM 8-pCPT-cGMP significantly depressed the sensitivity of [Ca2+]i to 5HT, and also myofilament sensitivity to calcium, but only in fetal arteries. In fetal basilar arteries contracted with 120 mM potassium, the EC30 for 8-pCPT-cGMP-induced relaxation was 25 microM. In fura-2 loaded ovine arteries, pretreatment with 25 microM 8-pCPT-cGMP had no effect on the ability of graded concentrations of potassium to elevate [Ca2+]i but reduced potassium's ability to induce contraction and attenuated myofilament calcium sensitivity; these latter effects were significant only in fetal arteries. In alpha-toxin permeabilized preparations, 25 microM 8-pCPT-cGMP significantly depressed both basal- and agonist-stimulated myofilament calcium sensitivity, only in fetal but not in adult basilars. Together, these results demonstrate that: (1) sensitivity to cGMP is greater in fetal than adult sheep arteries independent of method of contraction; (2) cGMP can reduce [Ca2+]i but only in agonist-contracted and not in potassium-contracted arteries; (3) and cGMP attenuates myofilament calcium sensitivity regardless of method of contraction. Overall, the data demonstrate that variations in the ability of cGMP to produce vasodilatation reflect age-, artery-, and agonist-dependent differences in the combination of mechanisms mediating responses to cGMP.
Nauli
S M
SM
Center for Perinatal Biology, Department of Physiology, Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.
Ally
A
A
Zhang
L
L
Gerthoffer
W T
WT
Pearce
W J
WJ
D000367:Age Factors; D000818:Animals; D001488:Basilar Artery / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D011188:Potassium / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D012756:Sheep; D013873:Thionucleotides / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*
D013873:Thionucleotides; D012701:Serotonin; C055656:8-((4-chlorophenyl)thio)cyclic-3',5'-GMP; D000242:Cyclic AMP; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D011188:Potassium; D002118:Calcium