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

Raf Lemmens, Olof Larsson, Per Olof Berggren, Md Shahidul Islam

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)9971-9977
Number of pages7
JournalJournal of Biological Chemistry
Volume276
Issue number13
DOIs
StatePublished - Mar 30 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Fingerprint Dive into the research topics of 'Ca<sup>2+</sup>-induced Ca<sup>2+</sup> Release from the Endoplasmic Reticulum Amplifies the Ca<sup>2+</sup> Signal Mediated by Activation of Voltage-gated L-type Ca<sup>2+</sup> Channels in Pancreatic β-Cells'. Together they form a unique fingerprint.

Cite this