Up-regulation of L- and non-L, non-N-type Ca2+ channels by basal and stimulated protein kinase C activation in insulin-secreting RINm5F cells.
We studied the effect of protein kinase C (PKC) inhibition and activation on voltage-dependent Ca2+ channels in rat insulinoma RINm5F cells. PKC down-regulation by chronic (24 h) treatment with the PKC activator phorbol 12-myristate 13-acetate (PMA) reduced by about 60% the Ba2+ currents through L- and non-L, non-N-type high-voltage-activated Ca2+ channels, indicating that PKC tonically up-regulates the two main Ca2+ channel subtypes of RINm5F cells under basal conditions. Consistently, PKC activation by acute PMA application caused only a modest increase (average 23%) of Ba2+ currents in a minority of cells (24%). L- and non-L, non-N-type channels were differentially up-regulated by either basal or stimulated PKC activation. Acute up-regulation was predominant on L-type channels and caused an I/V shift of the Ba2+ currents in the hyperpolarizing direction. Non-L, non-N-type channels were less affected by acute PMA application, possibly reflecting a more effective tonic PKC up-regulatory action. Unexpectedly, the increase of Ba2+ currents during acute PMA application was followed by a progressive current decrease, which was also observed in isolation in another 24% of the cells and could be ascribed to PKC-induced ATP depletion, rather than to a direct effect of PKC on Ca2+ channels. We also provide evidence that PKC-mediated phosphorylation is not involved in the G-protein-mediated noradrenergic modulation of Ca2+ channels in RINm5F cells.
Platano
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D
Dipartimento di Neuroscienze, Turin, Italy.
Pollo
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A
Carbone
E
E
Aicardi
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G
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001464:Barium / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology; D019256:Cadmium Chloride; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002460:Cell Line; D002712:Chlorides / Q000494:pharmacology; D004789:Enzyme Activation; D007340:Insulinoma; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D010190:Pancreatic Neoplasms; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D012044:Regression Analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002712:Chlorides; D010455:Peptides; D002104:Cadmium; D001464:Barium; D000255:Adenosine Triphosphate; D020866:omega-Conotoxin GVIA; D011494:Protein Kinases; D009543:Nifedipine; D019256:Cadmium Chloride; D013755:Tetradecanoylphorbol Acetate