The primary cilium of MDCK cells is mechanically sensitive and functions as a flow sensor, as demonstrated by increased intracellular calcium levels when the cilium is bent. This increase in calcium is initiated by Ca²+ influx through mechanically sensitive channels in the cilium or its base, followed by calcium release from IP3-sensitive stores. The calcium signal spreads as a wave through gap junctions to neighboring cells, indicating that flow sensing is a coordinated tissue-level event. Membrane potential measurements during perfusion showed hyperpolarization during elevated intracellular calcium, supporting the role of the cilium in flow sensing. The primary cilium of MDCK cells, which is visible under high-resolution DIC microscopy, is about 8 μm long one week after splitting and is well-suited for testing the hypothesis of its role as a mechanosensor. The study used Fluo-4-AM as a calcium indicator and measured calcium responses to mechanical bending of the cilium via micropipette suction or increased perfusion flow. The results suggest that the primary cilium in MDCK cells is mechanically sensitive and responds to flow by significantly increasing intracellular calcium. The study also included immunofluorescence and electrophysiology experiments to confirm the findings. The primary cilium of MDCK cells is a key structure for flow sensing, with mechanical deformation triggering calcium signaling that spreads through the tissue.The primary cilium of MDCK cells is mechanically sensitive and functions as a flow sensor, as demonstrated by increased intracellular calcium levels when the cilium is bent. This increase in calcium is initiated by Ca²+ influx through mechanically sensitive channels in the cilium or its base, followed by calcium release from IP3-sensitive stores. The calcium signal spreads as a wave through gap junctions to neighboring cells, indicating that flow sensing is a coordinated tissue-level event. Membrane potential measurements during perfusion showed hyperpolarization during elevated intracellular calcium, supporting the role of the cilium in flow sensing. The primary cilium of MDCK cells, which is visible under high-resolution DIC microscopy, is about 8 μm long one week after splitting and is well-suited for testing the hypothesis of its role as a mechanosensor. The study used Fluo-4-AM as a calcium indicator and measured calcium responses to mechanical bending of the cilium via micropipette suction or increased perfusion flow. The results suggest that the primary cilium in MDCK cells is mechanically sensitive and responds to flow by significantly increasing intracellular calcium. The study also included immunofluorescence and electrophysiology experiments to confirm the findings. The primary cilium of MDCK cells is a key structure for flow sensing, with mechanical deformation triggering calcium signaling that spreads through the tissue.