Protein kinase activation increases insulin secretion by sensitizing the secretory machinery to Ca2+.
Glucose and other secretagogues are thought to activate a variety of protein kinases. This study was designed to unravel the sites of action of protein kinase A (PKA) and protein kinase C (PKC) in modulating insulin secretion. By using high time resolution measurements of membrane capacitance and flash photolysis of caged Ca(2+), we characterize three kinetically different pools of vesicles in rat pancreatic beta-cells, namely, a highly calcium-sensitive pool (HCSP), a readily releasable pool (RRP), and a reserve pool. The size of the HCSP is approximately 20 fF under resting conditions, but is dramatically increased by application of either phorbol esters or forskolin. Phorbol esters and forskolin also increase the size of RRP to a lesser extent. The augmenting effect of phorbol esters or forskolin is blocked by various PKC or PKA inhibitors, indicating the involvement of these kinases. The effects of PKC and PKA on the size of the HCSP are not additive, suggesting a convergent mechanism. Using a protocol where membrane depolarization is combined with photorelease of Ca(2+), we find that the HCSP is a distinct population of vesicles from those colocalized with Ca(2+) channels. We propose that PKA and PKC promote insulin secretion by increasing the number of vesicles that are highly sensitive to Ca(2+).
Wan
Qun-Fang
QF
Institute of Biophysics and Biochemistry, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China.
Dong
Yongming
Y
Yang
Hua
H
Lou
Xuelin
X
Ding
Jiuping
J
Xu
Tao
T
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation; D005089:Exocytosis / Q000502:physiology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000502:physiology*; D008297:Male; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D022161:Transport Vesicles / Q000378:metabolism*
D015220:Calcium Channels; D007328:Insulin; D011494:Protein Kinases; D002118:Calcium