Figure 9.

Islet cell cilia do not respond with Ca²⁺ signaling following mechanical stimulation. (A) Schematic drawing of the cell press used to compress islets on the stage of a confocal microscope. (B) Confocal micrographs of a whole islet expressing Smo-GCaMP5G-mCh. Upper row shows mCherry fluorescence and bottom row shows GCaMP5G fluorescence. Notice how both mild compression and deformation is without effect on both cilia and cytosolic Ca²⁺. (C) Changes in cilia GCaMP5G/mCh fluorescence ratio during mild compression of a mouse islet (n = 49 cells). (D) GCaMP5G/mCh ratio change following strong compression with islet deformation for the indicated number of islets and islet cells. (E) Schematic drawing of the principle of mechanical stimulation using a glass pipette. (F) Confocal microscopy images of a MIN6 cell expressing Smo-GCaMP5G-mCh following exposure to mechanical stimulation (top) and depolarization (bottom). (G) Means ± SEM (n = 7) for the cilia and cell body GCaMP5G fluorescence change in response to mechanical stimulation and depolarization. The increase in cilia fluorescence upon depolarization is likely a contamination from the cytoplasm, which partially overlaps with the cilia in these recordings. (H) Proposed model for cilia-dependent Ca²⁺ signaling in β-cells. The primary cilium is isolated against cytosolic Ca²⁺ changes due to efficient Ca²⁺ extrusion in the cilium. This enables the cilium to utilize Ca²⁺ as an intrinsic signaling molecule. Activation of cilia-localized GABA_B1 receptors results in receptor mobilization into the cilium where it triggers local Ca²⁺ influx in a process that depends on L-type Ca²⁺ channel activation.