Melanocyte dendritic spine-like structures compartmentalize Ca²⁺ transients. (A) Schematic of confined Ca²⁺ transients (green) in dendritic spine-like structure and near the surface of melanocyte dendrites. See also Videos 6 and 7. (B) Dendrite from melanocyte expressing cytosolic mCherry and GCaMP6f in optimized co-culture with Ca²⁺ transients in a spine (1) and confined regions of the dendrite (2, 3). (C) Kymographs of GCaMP6f fluorescence signal, from the lines drawn through each of the three regions in B and the corresponding ΔF/F0 plot from a single ROI at the center of the signal. (D) Spread of Ca²⁺ signal (full width half maximum Gaussian fit, thick lines; raw data, thin lines) within the region (dashed line) for each location at the six indicated times corresponding to the peak marked with an asterisk in C. Region 1 has cytosolic mCherry signal indicating the physical boundaries of the spine. Scale bars, (B) 5 µm; (D) 1 µm.