Role of mitochondria in Ca2+ homeostasis of mouse pancreatic acinar cells

The effects of mitochondrial Ca2+ uptake on cytosolic Ca2+ concentration ([Ca2+]C) were investigated in mouse pancreatic acinar cells using cytosolic and/or mitochondrial Ca2+ indicators. When calcium stores of the endplasmic reticulum (ER) were emptied by prolonged incubation with thapsigargin (Tg) and acetylcholine (ACh), small amounts of calcium could be released into the cytosol (Delta[Ca2+](c) = 46 +/- 6 nM, n = 13) by applying mitochondrial inhibitors (combination of rotenone (R) and oligomycin (0)). However, applications of R/O, soon after the peak of Tg/Ach-induced Ca2+ transient, produced a larger cytosolic calcium elevation (Delta[Ca2+](c) = 84 +/- 6 nM, n = 9), this corresponds to an increase in the total mitochondrial calcium concentration ([Ca2+](m)) by approximately 0.4 mM. In cells pre-treated with R/O or Ru360 (a specific blocker of mitochondrial Ca2+ uniporter), the decay time-constant of the Tg/ACh-induced Ca2+ response was prolonged by approximately 40 and 80%, respectively. Tests with the mitochondrial Ca2+ indicator rhod-2 revealed large increases in [Ca2+](m) in response to Tg/ACh applications; this mitochondrial uptake was blocked by Ru360. In cells pre-treated with Ru360, 10 nM ACh elicited large global increases in [Ca2+](c), compared to control Cells in which ACh-induced Ca2+ signals were localised in the apical region. We conclude that mitochondria are active elements of cellular Ca2+ homeostasis in pancreatic acinar cells and directly modulate both local and global calcium signals induced by agonists. (C) 2002 Elsevier Science Ltd. All rights reserved.