The effect of cholesterol depletion by MβCD on Drosophila TRP and TRPL channels

Light activation of Drosophila photoreceptors leads to opening of two classes of Ca²⁺-permeable channels, the transient receptor potential (TRP) and the TRP-like (TRPL). These channels are activated by a G-protein-coupled PLC-signaling cascade, while the gating mechanism of the channels is still unknown. The TRP and TRPL are thought to be activated by a similar mechanism. Cholesterol is an essential component of cell membranes, which modulates the activity of many ion channels. It has been well established that application of methyl-β-cyclodextrin (MβCD) causes cholesterol depletion and modulates ion channel activity either directly or indirectly. Therefore, we investigated whether the Drosophila TRP and TRPL channels activity is affected by modulating plasma membrane cholesterol levels. Using whole-cell voltage-clamp measurements from photoreceptor cells, we examined the effect of cholesterol depletion on the response to light. MβCD reduced the amplitude and kinetics of the macroscopic light response in both TRP and TRPL channels. Further analysis of the TRP channels revealed that the change in the macroscopic response is a consequence of a reduction in the amplitude and frequency of the single-photon responses. Previous studies have shown that induction of metabolic stress (by CCCP) induced activation of the channels indirectly, while PUFA directly activated the channels. Application of CCCP in the presence of MβCD reduced the amplitude of the TRP and TRPL-dependent currents. However, the response of these channels to PUFA was not affected by the presence of MβCD. Our results suggest that cholesterol depletion suppressed the signal-transduction cascade upstream of Drosophila TRP and TRPL channels.