Bimodal role of conventional protein kinase C in insulin secretion from rat pancreatic beta cells.
The present study was conducted to evaluate the role of conventional protein kinase C (PKC) in calcium-evoked insulin secretion. In rat beta cells transfected with green fluorescent protein-tagged PKC-alpha (PKC-alpha-EGFP), a depolarizing concentration of potassium induced transient elevation of cytoplasmic free calcium ([Ca(2)(+)](c)), which was accompanied by transient translocation of PKC-alpha-EGFP from the cytosol to the plasma membrane. Potassium also induced transient translocation of PKC-theta-EGFP, the C1 domain of PKC-gamma and PKC-epsilon-GFP. A high concentration of glucose induced repetitive elevation of [Ca(2)(+)](c) and repetitive translocation of PKC-alpha-EGFP. Diazoxide completely blocked both elevation of [Ca(2)(+)](c) and translocation of PKC-alpha-EGFP. We then studied the role of conventional PKC in calcium-evoked insulin secretion using rat islets. When islets were incubated for 10 min with high potassium, Go-6976, an inhibitor of conventional PKC, and PKC-alpha pseudosubstrate fused to antennapedia peptide (Antp-PKC(19-31)) increased potassium induced secretion. Similarly, insulin release induced by high glucose for 10 min was enhanced by Gö-6976 and Antp-PKC(19-31). However, when islets were stimulated for 60 min with high glucose, both Gö-6976 and Antp-PKC(19-31) reduced glucose-induced insulin secretion. Similar results were obtained by transfection of dominant-negative PKC-alpha using adenovirus vector. Taken together, PKC-alpha is activated when cells are depolarized by a high concentration of potassium or glucose. Conventional PKC is inhibitory on depolarization-induced insulin secretion per se, but it also augments glucose-induced secretion.
Zhang
Hui
H
Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan.
Nagasawa
Masahiro
M
Yamada
Satoko
S
Mogami
Hideo
H
Suzuki
Yuko
Y
Kojima
Itaru
I
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007515:Islets of Langerhans / Q000201:enzymology* / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051381:Rats; D017208:Rats, Wistar
D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D049452:Green Fluorescent Proteins; C087857:protein kinase C gamma; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D005947:Glucose; D011188:Potassium; D002118:Calcium