Figure 1.

Mechanisms of changing the luminal width of glomerular capillaries shown in schematics. (A) Decreasing the capillary lumen (from A to B). Mesangial cell processes extend into the space between the endothelium and the glomerular basement membrane (GBM; arrows) and establish contacts to more peripheral sites of the GBM. By contraction, peripheral parts of the GBM (shown in brown) are pulled centripetally, and as seen in B, they are added to the paramesangial GBM. (B) Increasing the capillary lumen (from B to A). Mesangial cell processes disconnect from the GBM and retract (arrows). Thereby, the most peripheral portions of the paramesangial GBM (shown in brown) are released from the mesangium, and as seen in A, they are added to the peripheral portion leading to capillary expansion driven by the pressure gradient.