Phosphatidylinositol 3-kinase regulates Ca2+ signaling in pancreatic acinar cells through inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase.
Calcium is a key mediator of hormone-induced enzyme secretion in pancreatic acinar cells. At the same time, abnormal Ca(2+) responses are associated with pancreatitis. We have recently shown that inhibition of phosphatidylinositol 3-kinase (PI3-kinase) by LY-294002 and wortmannin, as well as genetic deletion of PI3-kinase-gamma, regulates Ca(2+) responses and the Ca(2+)-sensitive trypsinogen activation in pancreatic acinar cells. The present study sought to determine the mechanisms of PI3-kinase involvement in Ca(2+) responses induced in these cells by CCK and carbachol. The PI3-kinase inhibitors inhibited both Ca(2+) influx and mobilization from intracellular stores induced by stimulation of acini with physiological and pathological concentrations of CCK, as well as with carbachol. PI3-kinase inhibition facilitated the decay of cytosolic free Ca(2+) concentration ([Ca(2+)](i)) oscillations observed in individual acinar cells. The PI3-kinase inhibitors decreased neither CCK-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] production nor Ins(1,4,5)P(3)-induced Ca(2+) mobilization, suggesting that the effect of PI3-kinase inhibition is not through Ins(1,4,5)P(3) or Ins(1,4,5)P(3) receptors. PI3-kinase inhibition did not affect Ca(2+) mobilization induced by thapsigargin, a specific inhibitor of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA). Moreover, SERCA blockade with thapsigargin abolished the effects of pharmacological and genetic PI3-kinase inhibition on [Ca(2+)](i) signals, suggesting SERCA as a downstream target of PI3-kinase. Both pharmacological PI3-kinase inhibition and genetic deletion of PI3-kinase-gamma increased the amount of Ca(2+) in intracellular stores during CCK stimulation. Finally, addition of the PI3-kinase product phosphatidylinositol 3,4,5-trisphosphate to permeabilized acini significantly attenuated Ca(2+) reloading into the endoplasmic reticulum. The results indicate that PI3-kinase regulates Ca(2+) signaling in pancreatic acinar cells through its inhibitory effect on SERCA.
Veterans Affairs Greater Los Angeles Healthcare System, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90073, USA.
L
L
Fischer
A S
AS
Gukovskaya
S H
SH
Young
I
I
Gukovsky
A
A
Lugea
P
P
Buechler
J M
JM
Penninger
H
H
Friess
S J
SJ
Pandol
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009025:Morpholines / Q000494:pharmacology; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin / Q000494:pharmacology
D000252:Calcium-Transporting ATPases; D002217:Carbachol; D002766:Cholecystokinin; D002867:Chromones; D004791:Enzyme Inhibitors; D015544:Inositol 1,4,5-Trisphosphate; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one