The renal cell primary cilium functions as a flow sensor.
OBJECTIVE
To discuss recent reports on the function and importance of the renal primary cilium, a widely distributed organelle.


RESULTS
Most epithelial cells, including those in the kidney, express a solitary primary cilium. The primary cilium functions as a flow sensor in cultured renal epithelial cells (MDCK and mouse collecting tubule) mediating a large increase in intracellular calcium concentration. Flow sensing is shown to reside in the cilium itself and to involve the proteins polycystin 1 and 2, defects in which are associated with the majority of cases of human polycystic kidney disease. The role of the cilium in flow-dependent potassium secretion by the collecting tubule and in sensing of chemical components of the luminal fluid are also described.


CONCLUSIONS
The primary cilium is mechanically sensitive and serves as a flow sensor in cultured renal epithelia. Bending the cilium by mechanical means or flow causes a large, prolonged transient increase in intracellular calcium. The mechanically sensitive protein in the cilium is a polycystin.
Praetorius
Helle A
HA
Center for Salt and Water Research, University of Aarhus, Aarhus, Denmark. helle.praetorius@iekf.au.dk
Spring
Kenneth R
KR
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002923:Cilia / Q000502:physiology; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure*; D006801:Humans; D007668:Kidney / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure*; D008565:Membrane Proteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D050396:TRPP Cation Channels
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; D011506:Proteins; D050396:TRPP Cation Channels