Sphingosine metabolism induces Ca2+ oscillations in rat pancreatic acinar cells.
The possibility that sphingosine or a related metabolite could mediate inositol-1,4,5-triphosphate (1,4,5-IP3)-independent Ca2+ release in pancreatic acinar cells was investigated. In intact rat pancreatic acini superfused at 37 degrees C, sphingosine (10-100 microM) evoked, after a delay of several minutes, an increase in the cytosolic [Ca2+]i which was oscillatory below concentrations of 50 microM. At room temperature no increase in [Ca2+]i was observed. The increase in [Ca2+]i evoked by sphingosine was not inhibited by U73122, and thus was unlikely to be due to phosphatidylinositol (PI) hydrolysis. Furthermore, no PI hydrolysis or 1,4,5-IP3 production was detected on incubation with sphingosine. As metabolism of sphingosine could explain the temperature-dependent action, the effects of sphingosine and related sphingoid bases were tested in permeabilized cells. After a delay of 30 s at 37 degrees C, sphingosine evoked a slow increase in [Ca2+] into the medium. In contrast, addition of sphingosylphosphorylcholine (SPC) resulted in a rapid increase in [Ca2+]. This response was mimicked by 1,4,5-IP3 but not by addition of sphingosine phosphate (1-10 microM), ceramide (30 microM), or sphingomyelin (50 micrograms/ml). SPC appeared to induce release of Ca2+ from the same store as 1,4,5-IP3, as SPC failed to evoke any further increase in Ca2+ from cells previously depleted by addition of a maximal concentration of 2,4,5-IP3 or thapsigargin. 1,4,5-IP3 but not SPC-induced Ca2+ release was blocked by heparin, indicating that SPC-induced Ca2+ release was not mediated through the IP3 receptor-channel complex. This study demonstrates that SPC, a sphingosine metabolite, could be responsible for IP3-independent Ca2+ oscillations previously seen in pancreatic acinar cells.
Department of Physiology, University of Michigan, Ann Arbor 48109.
D I
DI
Yule
D
D
Wu
T E
TE
Essington
J A
JA
Shayman
J A
JA
Williams
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002766:Cholecystokinin / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009991:Oscillometry; D010179:Pancreas / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013110:Sphingosine / Q000378:metabolism* / Q000494:pharmacology*; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D004963:Estrenes; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011760:Pyrrolidinones; C049925:fura-2-am; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D015544:Inositol 1,4,5-Trisphosphate; D002766:Cholecystokinin; D010738:Type C Phospholipases; D013110:Sphingosine; D002118:Calcium; D016257:Fura-2