Pattern of rise in subplasma membrane Ca2+ concentration determines type of fusing insulin granules in pancreatic beta cells.
We simultaneously analyzed insulin granule fusion with insulin fused to green fluorescent protein and the subplasma membrane Ca2+ concentration ([Ca2+](PM)) with the Ca2+ indicator Fura Red in rat beta cells by dual-color total internal reflection fluorescence microscopy. We found that rapid and marked elevation in [Ca2+](PM) caused insulin granule fusion mostly from previously docked granules during the high KCl-evoked release and high glucose-evoked first phase release. In contrast, the slow and sustained elevation in [Ca2+](PM) induced fusion from newcomers translocated from the internal pool during the low KCl-evoked release and glucose-evoked second phase release. These data suggest that the pattern of the [Ca2+](PM) rise directly determines the types of fusing granules.
Department of Biochemistry, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, Tokyo 181-8611, Japan.
Mica
M
Ohara-Imaizumi
Kyota
K
Aoyagi
Yoko
Y
Nakamichi
Chiyono
C
Nishiwaki
Takashi
T
Sakurai
Shinya
S
Nagamatsu
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008561:Membrane Fusion; D008856:Microscopy, Fluorescence; D051381:Rats; D017208:Rats, Wistar; D022142:Secretory Vesicles / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure
D007328:Insulin; D002118:Calcium