  Bile, the central metabolic product of the liver, is secreted by hepatocytes
into bile canaliculi (BC), tubular subcellular structures of 0.5-2 $\mu$m
diameter which are formed by the apical membranes of juxtaposed hepatocytes. BC
interconnect to build a highly ramified 3D network that collects and transports
bile towards larger interlobular bile ducts (IBD). The transport mechanism of
bile is of fundamental interest and the current text-book model of "osmotic
canalicular bile flow", i.e. enforced by osmotic water influx, has recently
been quantitatively verified based on flux measurements and BC contractility
(Meyer et al., 2017) but challenged in the article entitled "Intravital dynamic
and correlative imaging reveals diffusion-dominated canalicular and
flow-augmented ductular bile flux" (Vartak et al., 2020). We feel compelled to
share a series of arguments that question the key conclusions of this study
(Vartak et al., 2020), particularly because it risks to be misinterpreted and
misleading for the field in view of potential clinical applications. We
summarized the arguments in the following 8 points.
