TRPML channel activation and recovery of calcium signals in pulmonary arterial myocytes of fetal and adult sheep disrupted by long term hypoxia

Abstract

Ca 2+ signals are important for regulating vasodilatory function in the pulmonary vasculature. Previous studies demonstrate that there are developmental changes in rapid Ca 2+ sparks and slower whole-cell Ca 2+ oscillations. Long-term hypoxia (LTH) causes pulmonary hypertension and aberrations in these Ca 2+ signals are thought to be important to the etiology of the disease. The LTH-induced dysregulation in Ca 2+ sparks is linked to loss in communication between L-type Ca 2+ channels on the plasma membrane and ryanodine receptors on the sarcoplasmic reticulum. Recent studies illustrate that Ca 2+ filled lysosomes can be closely associated with the sarcoplasmic reticulum. Previous work shows that activation of TRPML channels on lysosomes releases Ca 2+ into the cytosol and can trigger ryanodine receptor mediated Ca 2+ sparks. The aim of this study was to test if TRPML channel activation recovers aberrant Ca2+ sparks and whole-cell Ca 2+ oscillations after LTH exposure. Ca 2+ sparks and whole-cell Ca 2+ oscillations were measured on live fetal or adult sheep pulmonary arterial myocytes loaded with fluo-4 in an en face arterial preparation using confocal microscopy. The sheep were housed at either normoxic (700m) or hypoxic (3801m) conditions. Myocyte Ca 2+ was measured in the absence and then presence of 10 μM MLSA-1, a selective TRPML channel agonist. Treatment with MLSA-1 increased overall spark and oscillatory activity. In the fetal hypoxic group, MLSA-1 significantly increased the number of cells with oscillatory activity. MLSA-1 also significantly increased Ca 2+ spark activity in fetal and adult hypoxic, as well as adult normoxic myocytes. Interestingly, MLSA-1 did not influence amplitude of Ca 2+ sparks or the area of whole-cell Ca 2+ oscillatory events. These results suggest that activation of lysosomal TRPML channels may be a therapeutic target for pulmonary hypertension, through recovery of Ca 2+ signals that regulate pulmonary vascular reactivity. Still, further exploration is needed to fully understand the impact of LTH on lysosomal function, the mechanisms by which aberrant Ca 2+ signaling activity is recovered, and the effect on pulmonary vascular resistance and pressure. NIH R01HL155295, R01HL149608 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.