More Transparency in BioAnalysis of Exocytosis: Coupling of Electrochemistry and Fluorescence Microscopy at ITO Electrodes

Vesicular exocytosis is an essential biological mechanism used by cellular organisms to release bioactive molecules (hormones, neurotransmitters…) in their environment. For instance, this is the pathway by which chromaffin cells deliver catecholamines (adrenaline, nor-adrenaline, dopamine…) in blood. During this process, secretory vesicles that initially stored the (bio)chemical messengers dock to the cell membrane. The subsequent fusion of vesicle and cell membranes induces the formation of a fusion pore that initiates the first exchanges between the intravesicular and extracellular media. Its following expansion thus favours a larger release of the vesicular content into the external medium. Several analytical methods have been developed in order to study exocytosis at the single living cell level in real time. Among those techniques, mostly based on electric or optic measurements, amperometry with a carbon-fiber ultramicroelectrode [1], used in the first part of this report, and total internal reflection fluorescence microscopy (TIRFM) appear as the most powerful [2] Practically, physico-chemical properties of ultramicroelectrodes induce a high detection sensitivity and temporal resolution, thus being particularly well adapted to monitor exocytosis of electroactive molecules in real time.