Carboxamido steroids inhibit the opening properties of Transient Receptor Potential ion channels by lipid raft modulation.

Abstract

Transient Receptor Potential (TRP) cation channels, like the TRP Vanilloid 1 and TRP Ankyrin 1 (TRPV1 and TRPA1) are expressed on primary sensory neurons. These thermosensor channels play role in pain processing. We provided evidence that lipid raft disruption influenced the TRP channel activation and a carboxamido-steroid compound (C1) inhibited TRPV1 activation. Therefore, our aim was to investigate whether this compound exerts its effect through lipid raft disruption and the steroid backbone (C3) or altered position of the carboxamido group (C2) influence the inhibitory action by measuring Ca2+-transients on isolated neurons and calcium-uptake on receptor-expressing CHO cells. Membrane cholesterol content was measured by filipin staining and membrane polarisation by fluorescence spectroscopy. Both the percentage of responsive cells and the magnitude of the intracellular Ca2+-enhancement evoked by the TRPV1 agonist capsaicin were significantly inhibited after C1 and C2 incubation, but not after C3 administration. C1 was able to reduce other TRP channel activation as well. The compounds induced cholesterol depletion in CHO cells, but only C1 induced changes in membrane polarisation. The inhibitory action of the compounds on TRP channel activation develops by lipid raft disruption, and the presence and the position of the carboxamido group is essential.