TRPML Activation with MLSA1 Increases Ca 2+ Oscillations in Fetal Pulmonary Arterial Myocytes

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Ca2+ signaling in vascular myocytes is a highly regulated process and includes whole-cell oscillations and focal sub-cellular Ca2+ events. Previous evidence shows that activation of ryanodine receptors on the sarcoplasmic reticulum contributes to Ca2+ oscillations in pulmonary arterial myocytes. The oscillatory activity is thought to contribute to arterial reactivity and the regulation of vascular blood flow. Evidence also shows that long-term fetal hypoxia results in restricted oscillatory activity in the pulmonary arterial myocytes. We hypothesize that MLSA-induced TRPML activation can increase oscillatory activity in normoxic fetal pulmonary arterial myocytes. Activation of TRPML channels on the lysosome may elicit a triggering-pulse of Ca2+ that would drive RyR activity, rescuing intracellular oscillations in the pulmonary arterial myocytes. To study oscillatory activity, pulmonary arteries were isolated from near-term fetal sheep exposed to low altitude (700 m) for 110+ days. Intracellular oscillatory activity in the presence and absence of 10 μm MLSA1, a TRPML activator, was then measured using laser scanning confocal microscopy in Fluo-4 loaded pulmonary arterial myocytes. In preliminary studies, MLSA1 statistically increased overall oscillatory activity in normoxic myocytes. Further statistical analysis also revealed modest decreases in duration and area under the curve of oscillations as well as a significant increase in amplitude. Whether TRPML activation can be used to rescue aberrant RyR mediated arterial reactivity along with aberrant Ca2+ signaling in fetal pulmonary myocytes following gestational hypoxia remains to be determined.