Carbon fiber Amperometry
Carbon fiber electrodes were prepared by cannulating a 10 µm-diameter carbon fiber in polyethylene tubing (diameter: outer, 1 mm; inner, 0.5 mm). The carbon fiber tip was glued into a glass capillary for mounting on a patch-clamp headstage, and back filled with 3 M KCl to connect to the Ag/AgCl wire, which was kept at +700 mV. Amperometric currents were recorded using an EPC10 USB amplifier and PatchMaster software running on a PC computer. The sampling rate was 14.5 kHz. The sensitivity of the electrodes was routinely monitored before and after the experiments using 50 µM adrenaline as standard solution. Only fibers that rendered 200-300 pA of current increment after 50 µM adrenaline pulse were used for the experiments. The bath solution was the same used in the patch-clamp electrophysiology experiments.