Mechanosensory function of Cav1.2 calcium channel in renal primary cilia

Primary cilia are mechanosensory organelles and play an important role in calcium signaling. However, the precise mechanistic event of cilia‐calcium axis is still debated. Here, we used kidney cells transfected with G‐CaMP3 (a green fluorescent genetically encoded calcium indicator) to assess this important event in cell function. Using modified single‐cell imaging technique, we were able to capture a single‐living cell from the side for a better viewing of the cell body and its cilium simultaneously. Recently, we also used a high‐speed imaging recording (a minimum of 200 frames per sec) to capture both cilia bending and calcium signaling with Nomarski interference contrast (NIC) with fluorescence microscopy, respective. Within 1.5 μsec after fluid‐shear induce cilia bending, we reported calcium current was detected at the cell membrane very near to cilium base. This calcium current was directionally organized with the fluid flow and cilia bending direction. When ATP was added to the cells without flow, directionally non‐organized calcium current was seen throughout the cell membrane and cytosol. Immunofluorescence staining showed that Cav1.2 calcium channel expressed at the cell membrane close to cilia base. Verapamil completely abolished flow‐induced calcium signals suggesting that Cav1.2 channel might be responsible for calcium signaling. Calcium‐depleted extracellular fluid with EGTA produced a similar result as to verapamil indicating that extracellular calcium was required to initiate this event. We conclude that the very early event in cilium‐induced calcium signaling initiated in the cell membrane close to cilium base through Cav1.2 calcium channel. Support or Funding Information Department of Defense (PR130153 )