Developmental changes in ryanodine- and IP3-sensitive Ca2+ pools in ovine basilar artery

Abstract

To explore the hypothesis that cerebrovascular maturation alters ryanodine- and inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ pool sizes, we measured total intracellular Ca2+ with 45Ca and the fractions of intracellular Ca2+ released by IP3 and/or caffeine in furaptra-loaded permeabilized basilar arteries from nonpregnant adult and term fetal (139–141 days) sheep. Ca2+ mass (nmol/mg dry weight) was similar in adult (1.60 ± 0.18) and fetal (1.71 ± 0.16) arteries in the pool sensitive to IP3 alone but was significantly lower for adult (0.11 ± 0.01) than for fetal (1.22 ± 0.11) arteries in the pool sensitive to ryanodine alone. The pool sensitive to both ryanodine and IP3 was also smaller in adult (0.14 ± 0.01) than in fetal (0.85 ± 0.08) arteries. Because the Ca2+ fraction in the ryanodine-IP3 pool was small in both adult (5 ± 1%) and fetal (7 ± 4%) arteries, the IP3 and ryanodine pools appear to be separate in these arteries. However, the pool sensitive to neither IP3 nor ryanodine was 10-fold smaller in adult (0.87 ± 0.10) than in fetal (8.78 ± 0.81) arteries, where it accounted for 72% of total intracellular membrane-bound Ca2+. Thus, during basilar artery maturation, intracellular Ca2+ mass plummets in noncontractile pools, decreases modestly in ryanodine-sensitive pools, and remains constant in IP3-sensitive pools. In addition, age-related increases in IP3 efficacy must involve factors other than IP3 pool size alone.