Sphingosine inhibits muscarinic cholinergic receptor binding in rat parotid acinar cells.

1. Sphingosine inhibited the binding of [3H]quinuclidinyl benzilate (QNB), a potent and specific muscarinic antagonist, in dispersed rat parotid acinar cells. 2. The inhibition of [3H]QNB binding was expressed as decrease in affinity without significant change of a number of membrane sites. 3. The effect of sphingosine on the binding was not affected by the chelation of extracellular Ca2+. 4. H-7, an inhibitor of protein kinase C, failed to decrease [3H]QNB binding. 5. Stearylamine, an analogue of sphingosine, was as effective as sphingosine in inhibiting [3H]QNB binding. 6. These results suggest that sphingosine inhibits muscarinic cholinergic receptor binding by a mechanism that is independent on extracellular Ca2+ and protein kinase C.