Oxidative Stress and Ca 2+ Sparks in Pulmonary Arterial Myocytes of High Altitude Acclimatized Sheep

Abstract

High altitude (HA) can cause pulmonary hypertension and deregulate Ca2+ spark activity, which is due to local ryanodine receptor (RYR) activation and important to hypoxic-induced pulmonary vasoconstriction (HPV). HA also increases oxidative stress, which can impair Ca2+ spark activity. We tested the hypothesis that HA alters the impact of oxidative stress on Ca2+ spark activity in pulmonary arterial (PA) myocytes from low altitude (LA; 335m) and HA acclimatized adult sheep (~3,800m for <100 days). Ca2+ sparks were recorded using line-scan confocal imaging of the Ca2+ indicator Fluo-4. Oxidative stress was elevated with tert-butyl H2O2 (TbH2O2) or reduced with the antioxidant N-Acetyl-Cysteine (NAC). Ca2+ spark activity and spatial-temporal properties were analyzed with custom designed software (SparkLab). Oxidative stress decreased Ca2+ spark frequency in both LA and HA myocytes. NAC decreased frequency in HA but not LA myocytes. Spatial aspects of LA Ca2+ sparks were increased by both TbH2O2 and NAC, while HA decreased spatial aspects to TbH2O2. Temporal aspects in LA and HA were increased by NAC and TbH2O2. The alterations in Ca2+ spark activity in PA myocytes from LA and HA sheep support the premise that oxidative stress contributes to aberrant Ca2+ signaling seen following HA. Because RYRs are important to HPV, decreased Ca2+ spark activity following NAC in HA animals may indicate antioxidants can reduce pulmonary vascular pressures due to HA. This supports studies focused on resolving the mechanisms important to how HA mediated oxidative stress effects Ca2+ signaling (NIH and NSF support).