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

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