TY - JOUR
T1 - Ca2+-induced Ca2+ Release from the Endoplasmic Reticulum Amplifies the Ca2+ Signal Mediated by Activation of Voltage-gated L-type Ca2+ Channels in Pancreatic β-Cells
AU - Lemmens, Raf
AU - Larsson, Olof
AU - Berggren, Per Olof
AU - Islam, Md Shahidul
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2001/3/30
Y1 - 2001/3/30
N2 - Stimulus-secretion coupling in pancreatic β-cells involves membrane depolarization and Ca2+ entry through voltage-gated L-type Ca 2+ channels, which is one determinant of increases in the cytoplasmic free Ca2+ concentration ([Ca2+]i). We investigated how the endoplasmic reticulum (ER)-associated Ca2+ apparatus further modifies this Ca2+ signal. When fura-2-loaded mouse β-cells were depolarized by KCl in the presence of 3 mM glucose, [Ca2+]i increased to a peak in two phases. The second phase of the [Ca2+]i increase was abolished when ER Ca2+ stores were depleted by thapsigargin. The steady-state [Ca 2+li measured at 300 s of depolarization was higher in control cells compared with cells in which the ER Ca2+ pools were depleted. The amount of Ca2+ presented to the cytoplasm during depolarization as estimated from the integral of the increment in [Ca 2+]i over time (∫Δ[Ca2+] i·dt) was ∼30% higher compared with that in the Ca 2+ pool-depleted cells. neothapsigargin, an inactive analog, did not affect [Ca2+]i response. Using Sr2+ in the extracellular medium and exploiting the differences in the fluorescence properties of Ca2+- and Sr2+-bound fluo-3, we found that the incoming Sr2+ triggered Ca2+ release from the ER. Depolarization-induced [Ca2+]i response was not altered by U73122, an inhibitor of phosphatidylinositol-specific phospholipase C, suggesting that stimulation of the enzyme by Ca2+ is not essential for amplification of Ca2+ signaling. [Ca2+]i response was enhanced when cells were depolarized in the presence of 3 mM glucose, forskolin, and caffeine, suggesting involvement of ryanodine receptors in the amplification process. Pretreatment with ryanodine (100 μM) diminished the second phase of the depolarization-induced increase in [Ca 2+]i. We conclude that Ca2+ entry through L-type voltage-gated Ca2+ channels triggers Ca2+ release from the ER and that such a process amplifies depolarization-induced Ca 2+ signaling in β-cells.
AB - Stimulus-secretion coupling in pancreatic β-cells involves membrane depolarization and Ca2+ entry through voltage-gated L-type Ca 2+ channels, which is one determinant of increases in the cytoplasmic free Ca2+ concentration ([Ca2+]i). We investigated how the endoplasmic reticulum (ER)-associated Ca2+ apparatus further modifies this Ca2+ signal. When fura-2-loaded mouse β-cells were depolarized by KCl in the presence of 3 mM glucose, [Ca2+]i increased to a peak in two phases. The second phase of the [Ca2+]i increase was abolished when ER Ca2+ stores were depleted by thapsigargin. The steady-state [Ca 2+li measured at 300 s of depolarization was higher in control cells compared with cells in which the ER Ca2+ pools were depleted. The amount of Ca2+ presented to the cytoplasm during depolarization as estimated from the integral of the increment in [Ca 2+]i over time (∫Δ[Ca2+] i·dt) was ∼30% higher compared with that in the Ca 2+ pool-depleted cells. neothapsigargin, an inactive analog, did not affect [Ca2+]i response. Using Sr2+ in the extracellular medium and exploiting the differences in the fluorescence properties of Ca2+- and Sr2+-bound fluo-3, we found that the incoming Sr2+ triggered Ca2+ release from the ER. Depolarization-induced [Ca2+]i response was not altered by U73122, an inhibitor of phosphatidylinositol-specific phospholipase C, suggesting that stimulation of the enzyme by Ca2+ is not essential for amplification of Ca2+ signaling. [Ca2+]i response was enhanced when cells were depolarized in the presence of 3 mM glucose, forskolin, and caffeine, suggesting involvement of ryanodine receptors in the amplification process. Pretreatment with ryanodine (100 μM) diminished the second phase of the depolarization-induced increase in [Ca 2+]i. We conclude that Ca2+ entry through L-type voltage-gated Ca2+ channels triggers Ca2+ release from the ER and that such a process amplifies depolarization-induced Ca 2+ signaling in β-cells.
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U2 - 10.1074/jbc.M009463200
DO - 10.1074/jbc.M009463200
M3 - Article
C2 - 11139580
AN - SCOPUS:0035971143
VL - 276
SP - 9971
EP - 9977
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 13
ER -