Bending the MDCK cell primary cilium increases intracellular calcium

Area of Science:

• Cell Biology
• Renal Physiology
• Mechanobiology

Background:

• The primary cilium is a crucial organelle in renal epithelia.
• Its role in sensing mechanical stimuli, such as fluid flow, is not fully understood.

Purpose of the Study:

• To investigate the mechanical sensitivity of the primary cilium in renal epithelial cells.
• To determine if the primary cilium functions as a flow sensor.

Main Methods:

• Utilized differential interference contrast and fluorescence microscopy in Madin-Darby Canine Kidney (MDCK) cells.
• Applied mechanical stimuli via micropipette suction and controlled perfusate flow.
• Measured intracellular calcium levels using the fluorescent indicator Fluo-4.
• Assessed membrane potential changes using microelectrode recordings.

Main Results:

• Bending the primary cilium, through suction or increased flow, significantly elevated intracellular calcium levels.
• The calcium increase was initiated by influx through mechanosensitive channels, followed by release from IP3-sensitive stores.
• Calcium signals propagated as waves to neighboring cells via gap junctions, indicating coordinated tissue-level sensing.
• Elevated intracellular calcium was accompanied by profound membrane hyperpolarization.

Conclusions:

• The primary cilium in MDCK cells is mechanically sensitive and functions as a flow sensor.
• Flow-induced primary cilium activation leads to a coordinated calcium signaling response within the renal tissue.
• This mechanosensory function involves calcium influx, release from intracellular stores, and intercellular communication.