Ca2+ waves require sequential activation of inositol trisphosphate receptors and ryanodine receptors in pancreatic acini.
OBJECTIVE
The inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) and the ryanodine receptor (RyR) are the principal Ca2+-release channels in cells and are believed to serve distinct roles in cytosolic Ca2+ (Ca(i)2+) signaling. This study investigated whether these receptors instead can release Ca2+ in a coordinated fashion.


METHODS
Apical and basolateral Ca(i)2+ signals were monitored in rat pancreatic acinar cells by time-lapse confocal microscopy. Caged forms of second messengers were microinjected into individual cells and then photoreleased in a controlled fashion by either UV or 2-photon flash photolysis.


RESULTS
InsP3 increased Ca(i)2+ primarily in the apical region of pancreatic acinar cells, whereas the RyR agonist cyclic adenosine diphosphate ribose (cADPR) increased Ca(i)2+ primarily in the basolateral region. Apical-to-basal Ca(i)2+ waves were induced by acetylcholine and initiation of these waves was blocked by the InsP3R inhibitor heparin, whereas propagation into the basolateral region was inhibited by the cADPR inhibitor 8-amino-cADPR. To examine integration of apical and basolateral Ca(i)2+ signals, Ca2+ was selectively released either apically or basolaterally using 2-photon flash photolysis. Ca(i)2+ increases were transient and localized in unstimulated cells. More complex Ca(i)2+ signaling patterns, including polarized Ca(i)2+ waves, were observed when Ca2+ was photoreleased in cells stimulated with subthreshold concentrations of acetylcholine.


CONCLUSIONS
Polarized Ca(i)2+ waves are induced in acinar cells by serial activation of apical InsP3Rs and then basolateral RyRs, and subcellular release of Ca2+ coordinates the actions of these 2 types of Ca2+ channels. This subcellular integration of Ca2+-release channels shows a new level of complexity in the formation of Ca(i)2+ waves.
Leite
M Fatima
MF
Department of Physiology and Biophysics, UFMG, Belo Horizonte, Brazil.
Burgstahler
Angela D
AD
Nathanson
Michael H
MH
D000109:Acetylcholine / Q000494:pharmacology; D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology; D036563:Cyclic ADP-Ribose / Q000031:analogs & derivatives; D005343:Fibrinolytic Agents / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008297:Male; D018613:Microscopy, Confocal; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D010777:Photochemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005343:Fibrinolytic Agents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D014665:Vasodilator Agents; D036563:Cyclic ADP-Ribose; C082175:8-aminoadenosine cyclic 3',5'-(hydrogen phosphate) 5'-ribofuranosyl ester; D000246:Adenosine Diphosphate Ribose; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D000109:Acetylcholine; D002118:Calcium