Aims: 

Transient Receptor Potential ion channels, such as TRP Vanilloid 1 and Ankyrin repeat domain 1 (TRPV1 and TRPA1), are expressed in primary sensory neurons. TRPV1 can be activated by capsaicin, resiniferatoxin (RTX), low pH and noxious heat, TRPA1 by mustard oil (MO), allicin, cinnamaldehyde and formalin. Lipid rafts are defined as liquid ordered plasma membrane microdomains rich in cholesterol, sphingomyelin and gangliosides. Sphingomyelinase (SMase) decreases membrane sphingomyelin by hydrolization of sphingomyelin to phosphocholine and ceramide. Our earlier data suggest that lipid rafts in the neural membrane are involved in TRPV1 functions. The aim of the present study is to analyse the effects of lipid raft disruption by SMase on TRP ion channel activation.

Methods: 

Ratiometric technique of intracellular calcium measurement on cultured trigeminal cells and radioactive calcium-45 uptake experiments in TRPV1-expressing CHO cells were performed.

Results: 

SMase (30 mUN) significantly diminished the intracellular calcium-influx induced by capsaicin (330 nM), but had no significant effect on the calcium-uptake caused by RTX (3 nM) on TRPV1-expressing CHO cells. On cultured trigeminal neurons SMase had a concentration-dependent inhibitory effect both on capsaicin- and RTX-induced calcium-influx. SMase also diminished TRPA1 activation by MO (200 mM) and formalin (0.01%) on cultured trigeminal neurons. Activation of voltage-gated channels by KCl and administration of thapsigargin, which causes calcium release from inner store of the cells, remained unaltered.

Conclusion: 

These data suggest that disruption of lipid rafts inhibits the opening properties of TRP channels. The role of hydrophobic interactions of ligands at the TRPchannel/lipid raft interface might play more important role in drug action than it has previously been taken into account.

Support: 

OTKA NK78059, ETT 50017, SROP-4.2.1.B-10/2/KONV-2010-0002