Influence of ER leak on resting cytoplasmic Ca(2+) and receptor-mediated Ca(2+) signalling in human macrophage.

Mechanisms controlling endoplasmic reticulum (ER) Ca(2+) homeostasis are important regulators of resting cytoplasmic Ca(2+) concentration ([Ca(2+)]cyto) and receptor-mediated Ca(2+) signalling. Here we investigate channels responsible for ER Ca(2+) leak in THP-1 macrophage and human primary macrophage. In the absence of extracellular Ca(2+) we employ ionomycin action at the plasma membrane to stimulate ER Ca(2+) leak. Under these conditions ionomycin elevates [Ca(2+)]cyto revealing a Ca(2+) leak response which is abolished by thapsigargin. IP3 receptors (Xestospongin C, 2-APB), ryanodine receptors (dantrolene), and translocon (anisomycin) inhibition facilitated ER Ca(2+) leak in model macrophage, with translocon inhibition also reducing resting [Ca(2+)]cyto. In primary macrophage, translocon inhibition blocks Ca(2+) leak but does not influence resting [Ca(2+)]cyto. We identify a role for translocon-mediated ER Ca(2+) leak in receptor-mediated Ca(2+) signalling in both model and primary human macrophage, whereby the Ca(2+) response to ADP (P2Y receptor agonist) is augmented following anisomycin treatment. In conclusion, we demonstrate a role of ER Ca(2+) leak via the translocon in controlling resting cytoplasmic Ca(2+) in model macrophage and receptor-mediated Ca(2+) signalling in model macrophage and primary macrophage.