Calcium wave propagation in pancreatic acinar cells: functional interaction of inositol 1,4,5-trisphosphate receptors, ryanodine receptors, and mitochondria.
In pancreatic acinar cells, inositol 1,4,5-trisphosphate (InsP(3))-dependent cytosolic calcium ([Ca(2+)](i)) increases resulting from agonist stimulation are initiated in an apical "trigger zone," where the vast majority of InsP(3) receptors (InsP(3)R) are localized. At threshold stimulation, [Ca(2+)](i) signals are confined to this region, whereas at concentrations of agonists that optimally evoke secretion, a global Ca(2+) wave results. Simple diffusion of Ca(2+) from the trigger zone is unlikely to account for a global [Ca(2+)](i) elevation. Furthermore, mitochondrial import has been reported to limit Ca(2+) diffusion from the trigger zone. As such, there is no consensus as to how local [Ca(2+)](i) signals become global responses. This study therefore investigated the mechanism responsible for these events. Agonist-evoked [Ca(2+)](i) oscillations were converted to sustained [Ca(2+)](i) increases after inhibition of mitochondrial Ca(2+) import. These [Ca(2+)](i) increases were dependent on Ca(2+) release from the endoplasmic reticulum and were blocked by 100 microM ryanodine. Similarly, "uncaging" of physiological [Ca(2+)](i) levels in whole-cell patch-clamped cells resulted in rapid activation of a Ca(2+)-activated current, the recovery of which was prolonged by inhibition of mitochondrial import. This effect was also abolished by ryanodine receptor (RyR) blockade. Photolysis of d-myo InsP(3) P(4(5))-1-(2-nitrophenyl)-ethyl ester (caged InsP(3)) produced either apically localized or global [Ca(2+)](i) increases in a dose-dependent manner, as visualized by digital imaging. Mitochondrial inhibition permitted apically localized increases to propagate throughout the cell as a wave, but this propagation was inhibited by ryanodine and was not seen for minimal control responses resembling [Ca(2+)](i) puffs. Global [Ca(2+)](i) rises initiated by InsP(3) were also reduced by ryanodine, limiting the increase to a region slightly larger than the trigger zone. These data suggest that, while Ca(2+) release is initially triggered through InsP(3)R, release by RyRs is the dominant mechanism for propagating global waves. In addition, mitochondrial Ca(2+) import controls the spread of Ca(2+) throughout acinar cells by modulating RyR activation.
Straub
S V
SV
Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, New York 14642, USA.
Giovannucci
D R
DR
Yule
D I
DI
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010179:Pancreas / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D014475:Uncoupling Agents / Q000494:pharmacology
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D014475:Uncoupling Agents; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; D012433:Ryanodine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium