Depolarization-induced ERK phosphorylation depends on the cytosolic Ca2+ level rather than on the Ca2+ channel subtype of chromaffin cells.
The contribution of Ca2+ entry through different voltage-activated Ca2+ channel (VACC) subtypes to the phosphorylation of extracellular signal regulated kinase (ERK) was examined in bovine adrenal-medullary chromaffin cells. High K+ depolarization (40 mM, 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-alpha (PKC-alpha), but not on Ca2+/calmodulin-dependent protein kinase nor cyclic AMP-dependent protein kinase. Blockade of L-type Ca2+ channels by 3 microm furnidipine, or blockade of N channels by 1 micromomega-conotoxin GVIA reduced ERK phosphorylation by 70%, while the inhibition of P/Q channels by 1 micromomega-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 Ca2+ elevations elicited by 40 mm K+, showed that Ca2+ levels increased throughout the entire cytosol, both in the presence and the absence of Ca2+ channel blockers. Fifty-eight percent of the fluorescence rise depended on Ca2+ entering through N channels. Thus, ERK phosphorylation seems to depend on a critical level of Ca2+ in the cytosol rather than on activation of a given Ca2+ channel subtype.
Mendoza
Isabel E
IE
Centro de Neurociencia de Valparaíso, Universidad de Valparaíso, Chile.
Schmachtenberg
Oliver
O
Tonk
Ernesto
E
Fuentealba
Jorge
J
Díaz-Raya
Pamela
P
Lagos
Verónica L
VL
García
Antonio G
AG
Cárdenas
Ana M
AM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002417:Cattle; D016764:Cell Polarity / Q000187:drug effects; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D011188:Potassium; D002118:Calcium