Combined influence of ontogeny and chronic hypoxia on ryanodine receptor function in sheep pulmonary arteries and myocytes

Abstract

Ryanodine receptors (RyR) and associated Ca2+ spark events are important to hypoxic pulmonary vasoconstriction (HPV) and ET-1 dependent pulmonary arterial (PA) contractility. RyR function can change with development and chronic hypoxia (CH). Yet, the combined influence of CH and development on Ca2+ sparks is not known. We therefore tested the hypotheses that Ca2+ sparks are restricted before birth, that CH augments their activity, and that RyRs contribute to serotonin (5-HT)-mediated arterial stimulation. These hypotheses were tested on PA from near term fetal, 7–14 day old newborn and adult sheep that lived at low altitude or were maintained 100+ days at 3801 m (CH). Myography was performed on isolated PA and Ca2+ sparks were measured using fluo-4 loaded PA. Spark activity was greater in adults relative to fetuses and newborns. CH reduced spark activity in fetuses and newborns but not adults. Spark activity was reduced by 10 μM ryanodine (RY) in all groups except for CH fetuses. Selective RyR1/3 inhibition with 10 μM dantrolene suppressed sparks in normoxic fetuses and adults. Spark activity was not affected by 10 μM 5-HT in adult PA myocytes, and RY did not reduce 5-HT mediated PA contraction. Overall, RyR function increases following birth, CH differentially influences RyR function depending on developmental age, and 5-HT has little interaction with RyRs. NSF MRI 0923559 (SMW), NIH P01HD031226, R01HD003807 (LDL)