Insulinotropic glucagon-like peptide-1-mediated activation of non-selective cation currents in insulinoma cells is mimicked by maitotoxin.
Maitotoxin (MTX) activates a Ca2+-dependent non-selective cation current (ICa-NS) in insulinoma cells whose time course is identical to non-selective cation currents activated by incretin hormones such as glucagon-like peptide-1 (GLP-1), which stimulate glucose-dependent insulin secretion by activating cAMP signaling pathways. We investigated the mechanism of activation of ICa-NS in insulinoma cells using specific pharmacological reagents, and these studies further support an identity between MTX- and GLP-1-activated currents. ICa-NS is inhibited by extracellular application of genistein, econazole, and SKF 96365. This inhibition by genistein suggests that tyrosine phophorylation may play a role in the activation of ICa-NS. ICa-NS is not inhibited by incubation of cells in glucose-free solution, by extracellular tetrodotoxin, nimodipine, or tetraethylammonium, or by intracellular dialysis with 4-aminopyridine, ATP, ryanodine, or heparin. ICa-NS is also not significantly inhibited by staurosporine, which does, however, partially inhibit the MTX-induced rise of intracellular Ca2+ concentration. These effects of staurosporine suggest that protein kinase C may not be involved in the activation of ICa-NS but that it may regulate intracellular Ca2+ release. Alternatively, ICa-NS may have a small component that is carried through separate divalent cation-selective channels that are inhibited by staurosporine. ICa-NS is neither activated nor inhibited by dialysis with KF, KF + AlF3 or GTPgammaS (guanosine 5'-O-(3-thiotriphosphate)), suggesting that GTP-binding proteins do not play a major role in the activation of this current.
Leech
C A
CA
Laboratory of Molecular Endocrinology, Howard Hughes Medical Institute, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Habener
J F
JF
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D006224:Cricetinae; D004533:Egtazic Acid / Q000494:pharmacology; D052216:Glucagon-Like Peptide 1; D007093:Imidazoles / Q000494:pharmacology; D007340:Insulinoma; D007515:Islets of Langerhans; D008387:Marine Toxins / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D035964:Oxocins; D010190:Pancreatic Neoplasms; D010455:Peptides / Q000494:pharmacology*; D019311:Staurosporine / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000095702:Polyether Toxins
D002118:Calcium; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004533:Egtazic Acid; D052216:Glucagon-Like Peptide 1; D007093:Imidazoles; D008387:Marine Toxins; D035964:Oxocins; D010455:Peptides; D019311:Staurosporine; C020394:maitotoxin; D000095702:Polyether Toxins; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole