Cyclic Nucleotides Cause Divergent Ryanodine Receptor Modulation in Pulmonary Arterial Myocytes from Immature Chronic Hypoxic Sheep

Abstract

Calcium sparks are due to ryanodine receptor (RyR) activation and are intimate to local and global calcium signals in pulmonary arterial (PA) myocytes. RyRs are heavily regulated and cyclic nucleotides, including cAMP and cGMP, can increase RyR activity and thereby augment Ca2+ sparks and global Ca2+ waves. One possibility is that enhanced RyR activity contributes to altered pulmonary arterial reactivity responses found in sheep born at high altitude. Yet, the influence of chronic hypoxia (CH) on cyclic nucleotide regulation of RyRs is unknown. In these studies, we tested the hypothesis that cAMP and cGMP increase Ca2+ sparks and waves in PA myocytes from hypoxic sheep. Spark and wave activity was determined by visual analysis of line‐scan confocal recordings of Fluo‐4 or Fluo‐8 loaded PA from term‐fetal, ~ 10 day old, or adult sheep that lived at 3,200 meters for <100 days. Similar percentages of fetal, newborn, and adult myocytes had sparks and waves before cyclic nucleotide treatment, although newborns had more sparks per recording. cAMP and cGMP increased the number of adult cells with sparks and waves, yet, they respectively decreased the number of newborn and fetal myocytes with sparks. Spark activity was increased in adult myocytes by cGMP. The data suggest that cyclic nucleotides cause divergent regulation of RyRs from PA myocytes of immature CH sheep. NSF MRI 092355 (SMW), NIH P01HD031226, R01HD003807 (LDL)