Involvement of extracellular signal-regulated kinase (ERK) in pardaxin-induced dopamine release from PC12 cells

Pardaxin (PX), an ionophore-peptide neurotoxin isolated from the fish Pardachirus marmoratus, induces neurotransmitter release from neuronal preparations by both calcium-dependent and calcium-independent mechanisms. The aim of the present study was to investigate the role of extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) in pardaxin-induced dopamine (DA) release. The experiments were performed on variants of the PC12 cell line, an established cellular model for investigating DA release. Time course experiments indicated that PX, at nontoxic concentrations, stimulated ERK1 and ERK2 within 5 to 15 min, measured with a dual phospho-ERK antibody. PX stimulation of ERK activity was calcium (Ca²⁺)-dependent and followed by ERK translocation to the nucleus. This effect was temporally related to PX-induced exocytosis, and measured by [³H]dopamine release as well as by a vesicle fusion-based enzyme-linked immunosorbent assay. Blocking ERK activity with the specific mitogen-activated protein kinase kinase inhibitors PD98059 (50 μM for 45 min) and UO126 (30 μM for 30 min) inhibited PX-induced exocytosis in the presence but not in the absence of extracellular Ca²⁺. These results suggest the essential role of ERKs in PX-induced DA release under physiological conditions and support the hypothesis that ERKs are involved in regulating exocytosis.