The study by H.A. Praetorius and K.R. Spring investigates the hypothesis that the primary cilium of renal epithelia serves as a flow sensor in MDCK cells. Using differential interference contrast and fluorescence microscopy, they found that bending the cilium, either through suction with a micropipette or by increasing the flow rate of perfusate, significantly increases intracellular calcium levels as indicated by the fluorescent indicator Fluo-4. This calcium increase is initiated by Ca2+-influx through mechanically sensitive channels likely located in the cilium or its base, followed by calcium release from IP3-sensitive stores. The calcium signal spreads as a wave from the perturbed cell to its neighbors via gap junctions, suggesting that flow sensing is a coordinated event within the tissue. Additionally, the study observed a profound hyperpolarization of the membrane potential during the period of elevated intracellular calcium. The results conclude that the primary cilium in MDCK cells is mechanically sensitive and responds to flow by increasing intracellular calcium.The study by H.A. Praetorius and K.R. Spring investigates the hypothesis that the primary cilium of renal epithelia serves as a flow sensor in MDCK cells. Using differential interference contrast and fluorescence microscopy, they found that bending the cilium, either through suction with a micropipette or by increasing the flow rate of perfusate, significantly increases intracellular calcium levels as indicated by the fluorescent indicator Fluo-4. This calcium increase is initiated by Ca2+-influx through mechanically sensitive channels likely located in the cilium or its base, followed by calcium release from IP3-sensitive stores. The calcium signal spreads as a wave from the perturbed cell to its neighbors via gap junctions, suggesting that flow sensing is a coordinated event within the tissue. Additionally, the study observed a profound hyperpolarization of the membrane potential during the period of elevated intracellular calcium. The results conclude that the primary cilium in MDCK cells is mechanically sensitive and responds to flow by increasing intracellular calcium.