Perturbation by the PCB Mixture Aroclor 1254 of GABAA Receptor-Mediated Calcium and Chloride Responses during Maturation in Vitro of Rat Neocortical Cells

Abstract

GABAA receptors are targets of highly chlorinated environmental chemicals and have important roles in developing neurons. As such, we examined effects of polychlorinated biphenyls (PCBs) on GABAA receptor responses in primary cultures of rat neocortical cells using fluorescence imaging techniques. Between days in vitro (DIV) 5 and 8, the effect of GABAA receptor stimulation switched from excitatory (Ca2+ entry following a Cl− efflux; DIV ≤6) to inhibitory (Cl− influx without a Ca2+ rise; DIV ≥7). GABAA-receptor-stimulated increases in [Ca2+]i were diminished in a concentration-dependent (1–20 μM) manner following 1 h of exposure to the PCB mixture Aroclor 1254 (A1254), with significant reductions at concentrations as low as 2 μM. A1254 (1–20 μM) also led to concentration-dependent increases in basal [Ca2+]i, irrespective of DIV. A1254 (10 and 20 μM) significantly increased basal Ca2+i; the Ca2+i was elevated to 426 ± 39 nM by 20 μM A1254 but this concentration was not cytotoxic at 1 h. In addition, the mixture, A1254, as well as ortho- and non-ortho-chlorinated PCB congeners (IUPAC Nos. 4, 15, 126, and 138; 5–10 μM) individually decreased GABAA-stimulated Ca2+i responses and this tended not to depend on increases in basal Ca2+i. In cultures DIV 7 and older, A1254 (20 μM) also impaired inhibitory GABAA responses as evidenced by an ∼50% reduction of GABAA-stimulated Cl− influx (from ∼6 to 8 mM net accumulation in controls). The results demonstrate that: (1) GABAA receptor increases in Ca2+i and Cl−i are inhibited by 2–20 μM A1254, regardless of whether the responses are at excitatory or inhibitory stages of development; (2) Ca2+i homeostasis in cortical cells is disrupted by 10 μM A1254; yet (3) disruption of excitatory GABAA responses by A1254 or PCB congeners does not necessarily depend on impaired Ca2+ homeostasis. These novel observations suggest that GABAA receptor responses are a sensitive target for PCB effects in the rat developing nervous system.