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The William and Lenore Mote International Symposium 'Targets, thresholds and the burden of proof in fishery management' was held at the Mote Marine Laboratory, Sarasota, FL, USA, from 30 October to 2 November 2000.

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.