A method for measuring electrical signals in a primary cilium

In 47% of attempts, suction resulted in a seal with high input resistance. Single channels could be recorded while the cilium remained attached to the cell. When the pipette was raised into the air, the cell body was pulled off at the air-bath interface. The pipette retained the cilium and could then be immersed in various solutions that bathed the cytoplasmic face of the membrane. In excised cilia, ionic currents through ciliary channels were modulated by cytoplasmic Ca2+ and transmembrane voltage.Ciliary recording is a direct way to learn the effects of second messengers and voltage changes on ciliary transduction channels.Most cells in the body possess a single primary cilium [1], a thin process that projects from the surface of the cell. Defects in primary cilia are implicated in a wide range of human pathologies [2-5], including cystic kidney disease [6]. Primary cilia are thought to be cellular antennae; they detect chemical, mechanical, osmotic, and gravitational stimuli [7-11]. Evidence indicates that some sensory stimuli may be transduced into electrical signals via ion channels in primary cilia (for examples, see [12,13]). Several channel proteins (TRPP2, TRPC1, TRPV4, α-epithelial sodium channel) have been localized to primary cilia [8,14-18]. Additional channels have been studied in specialized cilia from other cells (for example, sperm [19], Chlamydomonas[20], photoreceptors [21], and olfactory receptor neurons [22,23]) or found in the ciliary proteome [24-27].Because of the primary cilium’s tiny size, direct examinations of the transduction of sensory to electrical signals in primary cilia are virtually non-existent. Instead, hypotheses of ciliary sensory function have been inferred from protein localizations, loss-of-function studies, and the effects of damaging or removing cilia [12,15,28]. There is now a substantial body of research characterizing the properties of ion channels relevant to primary cilia. Most investigators have taken indirect approa