Involvement of Ca2+, CaMK II and PKA in EGb 761-induced insulin secretion in INS-1 cells.
EGb 761, a standardized form of Ginkgo biloba L. (Ginkgoaceae) leaf extract, was recently reported to increase pancreatic beta-cell function. To determine whether EGb 761 elicits insulin secretion directly, we treated INS-1 rat beta cells with EGb 761 and then measured insulin release. Treatment of EGb 761 (50 microg/ml) significantly stimulated insulin secretion in INS-1 cells, compared with untreated control (p<0.05) and the stimulatory effect of EGb 761 on insulin secretion was dose-dependent. To elucidate the mechanism of EGb 761-induced insulin secretion, we investigated the involvement of calcium. The treatment with nifedipine, an L-type calcium channel blocker, prevented EGb 761-induced insulin secretion and furthermore, EGb 761 itself elevated [Ca(2+)](i), suggesting the involvement of calcium in this process. To identity the protein kinases involved in EGb 761-induced insulin secretion, INS-1 cells were treated with different kinase inhibitors and their effects on EGb 761-induced secretion were investigated. KN62 and H89, calium/calmodulin kinase (CaMK) II and protein kinase A (PKA) inhibitor, respectively, significantly reduced EGb 761-induced insulin secretion. Immunoblotting studies showed an increase in the phosphorylated-forms of CaMK II and of PKA substrates after EGb 761 treatment. Our data suggest that EGb 761-induced insulin secretion is mediated by [Ca(2+)](i) elevation and subsequent activation of CaMK II and PKA.
Choi
Sung-E
SE
Laboratory of Endocrinology, Institute for Medical Science, Ajou University School of Medicine, Youngtong-gu, Suwon, Kyunggi-do 442-749, Republic of Korea.
Shin
Ha-Chul
HC
Kim
Hyo-Eun
HE
Lee
Soo-Jin
SJ
Jang
Hyun-Ju
HJ
Lee
Kwan-Woo
KW
Kang
Yup
Y
D000818:Animals; D002118:Calcium / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D020441:Ginkgo biloba; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation; D010936:Plant Extracts / Q000494:pharmacology*; D051381:Rats; D000096983:Ginkgo Extract
D002118:Calcium; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D007328:Insulin; D010936:Plant Extracts; C063170:Ginkgo biloba extract; D000096983:Ginkgo Extract