Non-coplanar PCBs Induce Calcium Mobilization in Bottlenose Dolphin and Beluga Whale, but not in Mouse Leukocytes

Abstract

Polychlorinated biphenyls (PCBs) have been demonstrated to modulate marine mammal immune functions; however, the underlying mechanisms involved are poorly understood. Cytosolic calcium (Ca²⁺) is an important second messenger involved in numerous leukocyte functions. The direct effects of in vitro exposure to PCBs on Ca²⁺ mobilization were evaluated in leukocytes isolated from bottlenose dolphins, beluga whales, and B6C3F1 mice. Concentration- and time-response experiments with three non-coplanar PCBs (138, 153, 180), one coplanar PCB (169), and TCDD were tested. Exposure to the three non-coplanar PCBs significantly increased cytosolic Ca²⁺ in dolphin neutrophils, while PCB 180 significantly increased cytosolic Ca²⁺ in beluga neutrophils. Two non-coplanar PCBs (138 and 153) significantly increased Ca²⁺ in beluga monocytes, yet the response was delayed compared to that in neutrophils. Neither PCBs nor TCDD increased cytosolic Ca²⁺ in mouse neutrophils or monocytes. In experiments with Ca²⁺-free medium, only PCB 153 increased cytosolic Ca²⁺ in dolphin neutrophils, though the increase was less than that observed with Ca²⁺-supplemented medium, suggesting that extracellular Ca²⁺ was the predominant source for the rise in cytosolic Ca²⁺. Furthermore, in cells incubated with Ca²⁺-free medium, a significant increase in cytosolic Ca²⁺ was induced by thapsigargin following PCB exposure, indicating that intracellular Ca²⁺ was available, yet not mobilized by the PCBs, and further suggesting that PCBs mobilize extracellular Ca²⁺. These results demonstrate for the first time the direct effects of non-coplanar PCBs on Ca²⁺ mobilization in marine mammals, which may be involved in the modulation of phagocytosis previously observed in these species.

The authors acknowledge the staff at Mystic Aquarium and the U.S. Navy Marine Mammal Program for providing marine mammal blood samples. Funding for this work was provided by the NCER/STAR program of the U.S. Environmental Protection Agency, with initial funding from the University of Connecticut Research Foundation. Although the research described in this article has been funded wholly or in part by the U.S. Environmental Protection Agency through grant R-82836101-0 to Sylvain De Guise, it has not been subjected to the agency's required peer and policy review and therefore does not necessarily reflect the views of the agency and no official endorsement should be inferred.