Long term hypoxia impairs ryanodine receptor function and regulation by cyclic nucleotides in immature and mature pulmonary arterial myocytes

Abstract

Calcium sparks are due to ryanodine receptor (RyR) activation and are intimate to local and global Ca2+ signals in pulmonary arterial (PA) myocytes. One possibility is that impaired RyR activity contributes to altered PA reactivity following long‐term hypoxia (LTH) in developing arteries. Cyclic nucleotides (CNs), including cAMP and cGMP, can augment localized Ca2+ sparks and global Ca2+ waves due to RyR activation. Yet, the influence of LTH on CN regulation of RyRs of PA myocytes is unknown. These studies tested the hypothesis that cAMP and cGMP increase Ca2+ sparks and waves in PA myocytes and that LTH moderates this effect. Spark and wave activity was evaluated by visual analysis of line‐scan confocal recordings of PA myocytes from term‐fetal, ~ 10 day old, or adult sheep that lived at low (720 m) or at high altitude (3,200 m) for >;100 days. Similar percentages of term‐fetal, newborn, and adult myocytes had sparks and waves before CN treatment. LTH blunted spark activity and impaired CN reduction of sparks in fetus and adult. However, CNs inhibited sparks of LTH but not normoxic newborns. Ca2+ wave activity and regulatory influences by CNs were diminished by LTH in all age groups. The data suggest the effects of LTH on CN dependent regulation of RyRs may contribute to PA dysfunction and are highly dependent on the developmental age examined. (NSF MRI923559, NIH R03HD69746, P01HD31226, R01HD3807, LLU basic sciences fellowship)