Extracellular ATP stimulates exocytosis via localized Ca(2+) release from acidic stores in rat pancreatic beta cells.
Three different methods, membrane capacitance (C(m)) measurement, amperometry and FM dye labeling were used to investigate the role of extracellular ATP in insulin secretion from rat pancreatic beta cells. We found that extracellular application of ATP mobilized intracellular Ca(2+) stores and synchronously triggered vigorous exocytosis. No influence of ATP on the readily releasable pool of vesicles was observed, which argues against a direct modulation of the secretory machinery at a level downstream of Ca(2+) elevation. The stimulatory effects of ATP were greatly reduced by intracellular perfusion of BAPTA but not EGTA, suggesting a close spatial association of fusion sites with intracellular Ca(2+) releasing sites. ATP-induced Ca(2+) transients and exocytosis were not blocked by thapsigargin (TG), by a ryanodine receptor antagonist or by dissipation of pH in acidic stores by monensin alone, but they were greatly attenuated by IP(3) receptor inhibition as well as ionomycin plus monensin, suggesting involvement of IP(3)-sensitive acidic Ca(2+) stores. Taken together, our data suggest that extracellular ATP triggers exocytosis by mobilizing spatially limited acidic Ca(2+) stores through IP(3) receptors. This mechanism may explain how insulin secretion from the pancreas is coordinated through diffusible ATP that is co-released with insulin.
Joint Laboratory of Institute of Biophysics and Huazhong University of Science and Technology, National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing 100101, China.
Li
L
Xie
Ming
M
Zhang
Wei
W
Zhou
Zhengxing
Z
Wu
Jiuping
J
Ding
Liangyi
L
Chen
Tao
T
Xu
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002110:Caffeine / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D003620:Dantrolene / Q000378:metabolism; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009125:Muscle Relaxants, Central / Q000378:metabolism; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D019284:Thapsigargin / Q000378:metabolism
D015220:Calcium Channels; D004791:Enzyme Inhibitors; C073804:FM1 43; D005456:Fluorescent Dyes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007328:Insulin; D009125:Muscle Relaxants, Central; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D018160:Receptors, Cytoplasmic and Nuclear; D018048:Receptors, Purinergic P2; D019837:Ryanodine Receptor Calcium Release Channel; D002110:Caffeine; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D003620:Dantrolene; D002118:Calcium