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Depolarization‐induced ERK phosphorylation depends on the cytosolic Ca 2+ level rather than on the Ca 2+ channel subtype of chromaffin cells
Author(s) -
Mendoza Isabel E.,
Schmachtenberg Oliver,
Tonk Ernesto,
Fuentealba Jorge,
DíazRaya Pamela,
Lagos Verónica L.,
García Antonio G.,
Cárdenas Ana M.
Publication year - 2003
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2003.01965.x
Subject(s) - phosphorylation , depolarization , cytosol , kinase , protein kinase a , chromaffin cell , protein kinase c , mapk/erk pathway , chemistry , fura 2 , biology , microbiology and biotechnology , biophysics , biochemistry , endocrinology , adrenal medulla , catecholamine , enzyme
Abstract The contribution of Ca 2+ entry through different voltage‐activated Ca 2+ channel (VACC) subtypes to the phosphorylation of extracellular signal regulated kinase (ERK) was examined in bovine adrenal‐medullary chromaffin cells. High K + depolarization (40 m M , 3 min) induced ERK phosphorylation, an effect that was inhibited by specific mitogen‐activated protein kinase kinase inhibitors. By using selective inhibitors, we observed that depolarization‐induced ERK phosphorylation completely depended on protein kinase C‐α (PKC‐α), but not on Ca 2+ /calmodulin‐dependent protein kinase nor cyclic AMP‐dependent protein kinase. Blockade of L‐type Ca 2+ channels by 3 μ m furnidipine, or blockade of N channels by 1 μ m ω‐conotoxin GVIA reduced ERK phosphorylation by 70%, while the inhibition of P/Q channels by 1 μ m ω‐agatoxin IVA only caused a 40% reduction. The simultaneous blockade of L and N, or P/Q and N channels completely abolished this response, yet 23% ERK phosphorylation remained when L and P/Q channels were simultaneously blocked. Confocal imaging of cytosolic Ca 2+ elevations elicited by 40 m m K + , showed that Ca 2+ levels increased throughout the entire cytosol, both in the presence and the absence of Ca 2+ channel blockers. Fifty‐eight percent of the fluorescence rise depended on Ca 2+ entering through N channels. Thus, ERK phosphorylation seems to depend on a critical level of Ca 2+ in the cytosol rather than on activation of a given Ca 2+ channel subtype.