Figure 1. Sketch of the model domain consisting of an astrocyte network between arterial and venous paravascular spaces (PVS).

The network consists of several astrocyte units (AU) that each include one astrocyte (Ast) expressing aquaporin-4 (AQP4) water channels, extracellular space (ECS) and parts of the intracellular space of other cells including neurons, oligodendrocytes and microglia. Note that the schematic is not drawn to scale and does not represent the true ratio between intra- and extracellular space. The perivascular AUs are in direct contact with their neighbouring PVS via the respective astrocyte’s endfoot (EF). All astrocytes connect via endfeet to the basement membrane (BM) of the capillary associated with their AU. Neighbouring BMs connect to each other, and the perivascular BMs are additionally connected to the corresponding PVS (indicated by arrows in the figure). AQP4 covering each of these endfeet connect the capillary BMs or the PVS to the intra-astrocyte space. The intra-astrocyte and extracellular spaces within a given AU are in constant exchange of water through AQP4 water channels expressed in the astrocyte plasma membrane (PM). Gap junctions (GJ) connect the intracellular spaces of two adjacent astrocytes. PR: Astrocyte process. IEG: Inter-endfeet-gap.