Distinct mechanisms of neurotransmitter release from PC12 cells exposed to lead

Abstract

Two enzymes, protein kinase C and microsomal Ca2+‐ATPase help regulate levels of Ca2+ in many types of cells. Since proteins that regulate Ca2+ often influence sensitivity to Pb2+, we determined the possible roles played by protein kinase C and microsomal Ca2+‐ATPase for the Pb2+‐evoked release of norepinephrine (NOR) in PC 12 cells. NOR release was observed at 10 μM Pb2+ when PC 12 cells were stimulated with inhibitors of microsomal Ca2+‐ATPase such as thapsigargin, cyclopiazonic acid, or 2,5‐di‐(t‐butyl)‐hydroquinone. At 5 μM, Pb2+ evoked the release of NOR in PC 12 cells stimulated with activators of protein kinase C such as phorbol 12‐myristate 13‐acetate (PMA) or (‐)‐7‐octylindolactam. NOR release was observed at 1 μM Pb2+ in the presence of both PMA and thapsigargin. Ni2+ and Cd2+ blocked NOR release stimulated by Pb2+ in the presence of thapsigargin but not by PMA. NOR released by thapsigargin stimulation was not altered in PC 12 cells depleted of protein kinase C. Two proteins found in vesicles, chromogranin B and secretogranin‐II were released with NOR. Our results indicate that in PC 12 cells, Pb2+‐evokes the release of neurotransmitters. Furthermore, thapsigargin and PMA increase the cell's sensitivity to Pb2+ by different pathways. © 1996 Wiley‐Liss, Inc.

Ca2+‐independent vesicular catecholamine release in PC12 cells by nanomolar concentrations of Pb2+

“…3). The concentration of extracellular Pb 2+ required to induce exocytosis of catecholamine‐containing vesicles in intact, dexamethasone‐differentiated PC12 cells is comparable with previous results using suspensions of undifferentiated PC12 cells (Bressler et al . 1996) and bovine chromaffin cells (Tomsig and Suszkiw 1990).…”

“…The first effect observed is inhibition of evoked neurotransmitter release, which has been attributed to a reduced influx of Ca 2+ due to Ca 2+ channel block. The second, delayed effect of Pb 2+ is an enhancement of spontaneous neurotransmitter release, which occurs irrespective of the presence of extracellular Ca 2+ and has been attributed to intracellular effects of Pb 2+ (Manalis and Cooper 1973; Tomsig and Suszkiw 1993; Bressler et al . 1996; Braga et al .…”

“…2000). Previous reports demonstrate that addition of > 5 µ m Pb 2+ to external saline is required to induce neurotransmitter release from undifferentiated PC12 cell populations (Bressler et al . 1996).…”

Synaptotagmin I is a molecular target for lead

“…1984; Tomsig and Suszkiw 1993; Bielarczyk et al . 1994; Struzynska and Rafalowska 1994; Bressler et al . 1996; Bressler et al .…”

Increased AP‐1 DNA Binding Activity in PC12 Cells Treated with Lead

“…In this report the effect of Pb 2+ on the activation of AP‐1 was studied in the PC12 cell line. These cells release neurotransmitter in response to Pb 2+ (Bressler et al, 1996) and show induction of c‐ fos mRNA (Kim et al, 1997). Our results demonstrate an increase in AP‐1 DNA binding activity in PC12 cells exposed to lead acetate.…”