Frequency-dependent mitochondrial Ca(2+) accumulation regulates ATP synthesis in pancreatic β cells

Andrei I Tarasov, Francesca Semplici, Daliang Li, Rosario Rizzuto, Magalie A Ravier, Patrick Gilon, Guy A Rutter

Research output: Contribution to journalArticlepeer-review

54 Citations (Scopus)
19 Downloads (Pure)

Abstract

Pancreatic β cells respond to increases in glucose concentration with enhanced metabolism, the closure of ATP-sensitive K(+) channels and electrical spiking. The latter results in oscillatory Ca(2+) influx through voltage-gated Ca(2+) channels and the activation of insulin release. The relationship between changes in cytosolic and mitochondrial free calcium concentration ([Ca(2+)]cyt and [Ca(2+)]mit, respectively) during these cycles is poorly understood. Importantly, the activation of Ca(2+)-sensitive intramitochondrial dehydrogenases, occurring alongside the stimulation of ATP consumption required for Ca(2+) pumping and other processes, may exert complex effects on cytosolic ATP/ADP ratios and hence insulin secretion. To explore the relationship between these parameters in single primary β cells, we have deployed cytosolic (Fura red, Indo1) or green fluorescent protein-based recombinant-targeted (Pericam, 2mt8RP for mitochondria; D4ER for the ER) probes for Ca(2+) and cytosolic ATP/ADP (Perceval) alongside patch-clamp electrophysiology. We demonstrate that: (1) blockade of mitochondrial Ca(2+) uptake by shRNA-mediated silencing of the uniporter MCU attenuates glucose- and essentially blocks tolbutamide-stimulated, insulin secretion; (2) during electrical stimulation, mitochondria decode cytosolic Ca(2+) oscillation frequency as stable increases in [Ca(2+)]mit and cytosolic ATP/ADP; (3) mitochondrial Ca(2+) uptake rates remained constant between individual spikes, arguing against activity-dependent regulation ("plasticity") and (4) the relationship between [Ca(2+)]cyt and [Ca(2+)]mit is essentially unaffected by changes in endoplasmic reticulum Ca(2+) ([Ca(2+)]ER). Our findings thus highlight new aspects of Ca(2+) signalling in β cells of relevance to the actions of both glucose and sulphonylureas.

Original languageEnglish
Pages (from-to)543-554
Number of pages12
JournalPflugers Archiv European Journal of Physiology
Volume465
Issue number4
Early online date14 Nov 2012
DOIs
Publication statusE-pub ahead of print - 14 Nov 2012

Keywords

  • Action Potentials
  • Adenosine Diphosphate/metabolism
  • Adenosine Triphosphate/biosynthesis
  • Animals
  • Calcium/metabolism
  • Calcium Channels/metabolism
  • Calcium Signaling
  • Cells, Cultured
  • Cytosol/metabolism
  • Endoplasmic Reticulum/metabolism
  • Female
  • Glucose/metabolism
  • Insulin/metabolism
  • Insulin-Secreting Cells/metabolism
  • Mice
  • Mitochondria/metabolism

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