Spatial decay of the amperometric signal with melatonin. (A) Schematic of spatial measurements of melatonin (Mel) diffusion from a cell with successive carbon fiber placements (arrows) at 30-µm increments from the cell. (B) Results of an experiment with the melatonin pipette patched on a tsA201 cell before breakthrough. (C) A different tsA201 cell after breakthrough to whole-cell configuration. (D) The same kind of experiment as in B and C with a rat pinealocyte showing the transition from on-cell to whole-cell recording. Again, the carbon fiber is brought to the cell surface three times with each configuration, and then it is moved to points successively 30 µm away. (E) Mean spatial concentration profiles for on-cell and whole-cell experiments with tsA201 and pineal cells (n = 5–6). Error bars show SEM.