Protein kinase A- and C-induced insulin release from Ca2+ -insensitive pools.
Insulin secretion is known to depend on an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). However, recent studies have suggested that insulin secretion can also be evoked in a Ca(2+)-independent manner. In the present study we show that treatment of intact mouse islets and RINm5F cells with protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) or protein kinase A (PKA) activator forskolin promoted insulin secretion with no changes of [Ca(2+)](i). Moreover, insulin secretion mediated by PMA or forskolin was maintained even when extracellular or cytosolic Ca(2+) was deprived by treatment of cells with ethylene glycol bis(beta-amino ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or 1,2-bis(2-amino phenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxy methyl ester) (BAPTA/AM) in RINm5F cells. The secretagogue actions of PMA and forskolin were blocked by GF109203X and H89, selective inhibitors for PKC and PKA, respectively. PMA treatment caused translocation of PKC-alpha and PKC- epsilon from cytosol to membrane, implying that selectively PKC-alpha and PKC- epsilon isoforms might be important for insulin secretion. Co-treatment with high K(+) and PMA showed a comparable level of insulin secretion to that of PMA alone. In addition, PMA and forskolin evoked insulin secretion in cells where Ca(2+)-dependent insulin secretion was completed. Our data suggest that PKC and PKA can elicit insulin secretion not only in a Ca(2+)-sensitive manner but also in a Ca(2+)-independent manner from separate releasable pools.
Lee
Ihn-Soon
IS
Department of Life Science, Division of Molecular and Life Science, Pohang University of Science and Technology, POSTECH, San 31, Hyoja Dong, Pohang 790-784, Republic of Korea.
Hur
Eun-Mi
EM
Suh
Byung-Chang
BC
Kim
Mean-Hwan
MH
Koh
Duk-Su
DS
Rhee
In-Ja
IJ
Ha
Hyunjung
H
Kim
Kyong-Tai
KT
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D005089:Exocytosis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007527:Isoenzymes / Q000502:physiology; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D011493:Protein Kinase C / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007328:Insulin; D007527:Isoenzymes; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium