Abstract 12882: Reduced Mitochondrial and Sarcoplasmic Reticulum Calcium Buffering is Associated with Increased Cytosolic Calcium in Smooth Muscle Cells From Pulmonary Arterial Hypertension Patients
Introduction: Cytosolic calcium, [Ca2+]cyto, has a critical role in regulating cell proliferation and vascular tone in pulmonary arterial hypertension (PAH). However intramitochondrial calcium, [Ca2+]mito,has not been measured. This is relevant because the mitochondria in pulmonary artery smooth muscle cells (PASMCs) from PAH patients are fragmented due to increased fission. We hypothesized that mitochondrial Ca2+ buffering is abnormal in PAH.
Methods: [Ca2+]mito was measured in PASMC cultures from PAH and control patients using a Ca2+-sensitive FRET probe (CFP-calmodulin-YFP construct) with confocal microscopy. Measurements were made at baseline and after blocking fission, using the inhibitor of dynamin related protein-1, MDIVI-1. This FRET probe’s emissions depend on its calmodulin conformation, as determined by bound Ca2+ levels. [Ca2+]cyto was assessed by Fura-2’s 340/380nm emission ratio, measured at 510nm.
Results: [Ca2+]mito was reduced in PAH vs control PASMCs. MDIVI-1 restored mitochondrial fusion but further decreased [Ca2+]mito (Figure 1.) by 36.3% (PAH) and 37.6% (control). Conversely, MDIVI-1 further increased [Ca2+]cyto, particularly in PAH PASMC (control basal: 0.58+0.02; control MDIVI-1 0.70+0.03, n=23; PAH basal: 0.62+0.02, PAH MDIVI-1: 1.17+0.14, n=24). Inhibiting SR Ca2+ reuptake, by cyclopiazonic acid, increased [Ca2+]cyto more in control cells vs PAH PASMC.
Conclusion: SR and mitochondrial Ca2+ buffering capacity is reduced in PAH PASMC, perhaps explaining the high [Ca2+]cyto. While inhibiting mitochondrial fission corrects the mitochondrial networks structure, it further decreases [Ca2+]mito and raises[Ca2+]cyto. The importance of reciprocal changes in mitochondrial and cytosolic Ca2+ to vascular tone and proliferation is unknown.
- © 2011 by American Heart Association, Inc.