Because ceramide accumulates in several forms of cardiovascular disease and ceramide-induced apoptosis may involve the volume-sensitive Cl− current, ICl,swell, we assessed whether ceramide activates ICl,swell.
Methods and results
ICl,swell was measured in rabbit ventricular myocytes by whole-cell patch clamp after isolating anion currents. Exogenous C2-ceramide (C2-Cer), a membrane-permeant short-chain ceramide, elicited an outwardly rectifying Cl− current in both physiological and symmetrical Cl− solutions that was fully inhibited by DCPIB, a specific ICl,swell blocker. In contrast, the metabolically inactive C2-Cer analogue C2-dihydroceramide (C2-H2Cer) failed to activate Cl− current. Bacterial sphingomyelinase (SMase), which generates endogenous long-chain ceramides as was confirmed by tandem mass spectrometry, also elicited an outwardly rectifying Cl− current that was inhibited by DCPIB and tamoxifen, another ICl,swell blocker. Bacterial SMase-induced current was partially reversed by osmotic shrinkage and fully suppressed by ebselen, a scavenger of reactive oxygen species. Outward rectification with physiological and symmetrical Cl− gradients, block by DCPIB and tamoxifen, and volume sensitivity are characteristics that identify ICl,swell. Insensitivity to C2-H2Cer and block by ebselen suggest involvement of ceramide signalling rather than direct lipid-channel interaction.
Exogenous and endogenous ceramide elicited ICl,swell in ventricular myocytes. This may contribute to persistent activation of ICl,swell and aspects of altered myocyte function in cardiovascular diseases associated with by ceramide accumulation.