Ryanodine Receptor-Mediated Rapid Increase in Intracellular Calcium Induced by 7,8-Benzo(a)Pyrene Quinone in Human and Murine Leukocytes

Abstract

Benzo(a)pyrene (BaP) is an environmentally prevalent polycyclic aromatic hydrocarbon (PAH) known to produce immunotoxicity in murine and human lymphocytes. Previous studies by our lab have shown that certain BaP metabolites increase intracellular Ca²⁺ in human and murine lymphocytes. The mechanism by which these BaP metabolites increase Ca²⁺ may involve src kinase activation and mitochondrial oxidative stress. We have implicated a new pathway of Ca²⁺ elevation in lymphocytes produced by a novel BaP metabolite, BaP-7,8-dione (7,8-BPQ). This ortho quinone is produced from BaP-7,8-dihydrodiol by aldoketoreductase 1C1 (AKR1C) isoforms in human cells. We have previously shown that 7,8-BPQ increases Ca²⁺ levels in an in vitro rabbit skeletal muscle sarcoplasmic reticulum (SR) vesicle model via interaction with ryanodine receptors (RyR). In the present study, we found that 7,8-BPQ produced a RyR-dependent rapid increase in intracellular Ca²⁺ in the Daudi human B cell line. However, other BP-diones including 1,6-, 3,6-, and 6,12-BPQs failed to produce a rapid increase in Ca²⁺. Instead they produced a late increase in intracellular Ca²⁺, presumably via a redox-cycling-dependent loss of Ca²⁺ buffering capacity by mitochondria. Functional RyR were detected in Daudi using a ³H-ryanodine binding assay. The studies were extended to normal human peripheral blood and murine spleen cells, where it was found that 7,8-BPQ rapidly elevated intracellular Ca²⁺ in B cells and T cells in both species. The Ca²⁺-elevating effect of 7,8-BPQ was prevented by pretreatment with a high concentration of ryanodine (500 μM). Collectively, these results demonstrate a novel mechanism of Ca²⁺ elevation by an environmentally relevant metabolite of BaP in murine and human lymphocytes.