Patch clamp of primary cilia. (A, top) A patch pipette sealed to the membrane of a primary cilium (identified by GFP-tagged Smo) from RPE cells. (middle) The pipette is raised in order to pull the cilium from the plasma membrane. (bottom) The excised cilium remains attached to the pipette but detached from the cell. (B) Single channel openings in the ciliary membrane are potentiated by application of ATP in the on-cilia configuration. (C) Whole ciliary currents before and after cilia excision show that the majority of the current is conducted by channels in the ciliary membrane and not indirectly via channels in the plasma membrane. The current outwardly rectifies similar to other TRP currents. Modified from DeCaen et al. (2013) with permission from Nature Publishing Group.