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.