Sphingosine stimulates calcium mobilization in rat parotid acinar cells

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Abstract
In fura‐2‐loaded parotid acinar cells, 50–200 μM sphingosine induced an increase in cytosolic Ca2+ ([Ca2+]i). When extracellular Ca2+ was chelated by EGTA, 50 μM sphingosine failed to increase [Ca2+]i, but 100 or 200 μM sphingosine induced a slight and transient increase in [Ca2+]i. The addition of LaCl3 to the medium resulted in the same effect as chelation of extracellular Ca2+. When cells were incubated in low Ca2+ medium containing sphingosine, and extracellular Ca2+ was subsequently added, a rapid increase in [Ca2+]i depending on the concentration of sphingosine was shown. In low Ca2+ medium, a slight increase in [Ca2+]i induced by high concentrations of sphingosine was not shown after the transient increase in [Ca2+]i elicited by methacholine. Inhibitors of protein kinase C, H‐7 and K252a, did not mimic the effect of sphingosine on [Ca2+]i. These results suggest that sphingosine stimulates Ca2+‐influx and further stimulates the release of Ca2+ from agonist‐sensitive intracellular pools by a mechanism that is independent of protein kinase C.