Abstract
We examined the effect of sphingosine, the basic unit of sphingolipids, on GTPγS-stimulated [3H]inositol trisphosphate ([3H]InsP3) formation in electrically permeabilized rat parotid acinar cells prelabeled with [3H]inositol. GTPγS-stimulated[3H] InsP3 formation was inhibited by sphingosine in a concentration-dependent fashion. The [3H] InsP3 formation evoked by NaF and AlCl3 was also inhibited by sphingosine in a concentration-dependent manner. [3H]InsP3 formation was also activated by 1.2μM Ca2+, but sphingosine failed to inhibit the Ca2+-induced [3H]InsP3 formation. The protein kinase C inhibitor H-7 did not mimic the effect of sphingosine on GTPγS-induced [3H]InsP3 formation. These results suggest that sphingosine inhibits phospholipase C activity coupled to GTP-binding protein. However, the effect of sphingosine is not due to the inhibition of protein kinase C.
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