The role of Cholesterol in renal transepithelial transport 

 By Corina Balut

To address the recent findings that membrane associated proteins are likely to be affected by the lipid composition of their environment, this study focused on analyzing transepithelial Na⁺ transport in a reduced membrane cholesterol environment. Polarized monolayers of A6 cells, originating from Xenopus laevis renal distal tubules, were mounted in an Ussing-type chamber. Short-circuit current (I_SC) and transepithelial conductance (G_T) were recorded before and after cholesterol depletion treatment applied on apical side, by perfusing the cells with 20 mM methyl-ß-cyclodextrin (MßCD) for 60 min at room temperature.  
MßCD treatment did not significantly affect the amiloride-sensitive sodium current in steady state conditions. However, in response to hypo-osmotic shock treated cells showed a reduction in I_sc stimulation of 40% and for G_T with 44%. 
Since the analysed activating procedure of Na⁺ reabsorption involves ENaC (vesicular) trafficking and insertion into the membrane, the importance of membrane cholesterol for this process is emphasized. Consequently, treatments intending to inhibit cholesterol synthesis, like statins, could interfere with sodium and chloride homeostasis.
We now intend to further investigate the co-operative role of proteins and lipids (very often organized in domains) in controlling cell function and response to environmental stimuli, such as heavy metals and effects of ischemia/hypoxia. To accomplish this goal a combined approach, that implies electrophysiological and laser scan confocal microscopy measurements, together with the required experimental tools will be developed.