Liver sinusoidal endothelial cells (LSECs) are the filtration interface between blood and the interior of the liver. This molecular sieve consists of small holes with a diameter of 50-300 nm, called “fenestrations”. These dynamic structures, which open and close, can be influenced by various agents and their number and diameter are reduced with ageing. The regulation mechanisms and structure of fenestrations are not yet completely fully understood. During the last 40 years, LSECs have been studied using various imaging techniques, however, only recent developments in super-resolution microscopy have enabled visualization of fenestrations in near physiological conditions. Here, we present our results of studies on LSEC fenestration structure with the whole range of imaging techniques – from electron microscopy (SEM, TEM), through atomic force microscopy (AFM) and optical super-resolution nanoscopy (SIM, dSTORM, STED). Using different microscopic methods we are trying to find the mechanism(s)/protein(s) and substance(s) that influence and/or control the dynamics of fenestrations. Preliminary results show increases in porosity by xanthines, sildenafil and its analogues without any alterations in endocytosis. Further investigation will reveal if these treatments can reverse reduced porosity observed in aging.