Effects of Sphingomyelin Hydrolysis on Quantal Release from Rat Adrenal Chromaffin Cells.

摘要

Sphingomyelin (SM), a sphingolipid that is concentrated in the extracellular leaflet of the plasma membrane, can interact with cholesterol to form more ordered "raft" domains. The hydrolysis of SM by sphingomyelinase (SMase) generates ceramide and may redistribute cholesterol molecules to other less ordered domains. I employed carbon fibre amperometry to examine whether SM hydrolysis affected the kinetics of release of catecholamines from individual granules of rat chromaffin cells when exocytosis was triggered by elevated extracellular [K+]. Similar to cholesterol overload, SMase treatment selectively increased the proportion of "stand-alone foot" signals and the duration of the "pre-spike foot" signals; both effects could be reduced by extraction of cellular cholesterol. In contrast, the application of an exogenous ceramide did not mimic the effects of SMase. My results suggest that SMase treatment liberated cholesterol from lipid rafts to increase the persistence of the semi-stable fusion pore before the onset of rapid dilation.