Calcium is a key second messenger that can be mobilized from both the extracellular medium and intracellular calcium stores. Pulmonary arterial smooth muscle cells (PASMCs) respond to stretch by a calcium increase, a mechanism enhanced during pulmonary hypertension (PH). We investigated the role of the spatial organization between plasma membrane stretch-activated channels (SACs) and intracellular calcium stores [sarcoplasmic reticulum (SR), mitochondria, and lysosomes) in response to stretch.Methods and results
Studies were performed in freshly isolated PASMCs from both control and two different rat models of PH (chronically hypoxic and monocrotaline-treated rats). Co-immunolabellings revealed that the subcellular segregation between each subtype of SR ryanodine receptors (RyR1, RyR2, and RyR3), SERCA2 pumps (SERCA2a and SERCA2b), mitochondria, or lysosomes in freshly isolated PASMCs differs from control and PH PASMCs. In control PASMCs, stretching the membrane activates a Ca2+ influx through SACs. This influx is amplified by cell hyperpolarization, a calcium release by subplasmalemmal RyR1 and is then buffered by mitochondria. In two different PH rat models, the calcium response to stretch is enhanced due to hyper-reactivity of SACs and a greater calcium amplification by all RyR subtypes.Conclusion
The spatial organization of RyR and calcium stores in PASMCs is important for cell signalling and plays a causal role in PH.