Rapid exocytosis kinetics measured by amperometry within volcano microelectrodes

For over 30 years, carbon fiber microelectrodes have been the gold standard for measurements related to exocytosis and more generally to the processes taking place at the synaptic level. However, this method has a low throughput and molecules can escape detection due to the featureless nature of the planar microelectrodes it uses. Here we present a new electrochemical sensor that addresses these limitations. It is based on insulated protruding volcano-shaped tips of 2 mu m in diameter housing two individually addressable microelectrodes. The sensor enables volume confined and parallelizable recordings of exocytosis from adherent cells. Exocytotic releases from PC12 cells measured by amperometry on our device have quantal size in agreement with commonly admitted values but happen on a much smaller time scale; mostly within half a millisecond. We demonstrate that this faster kinetics must involve a faster vesicle fusion mechanism and is plausibly due to perturbation of the plasma membrane brought by the topography of our sensor. This suggests that exocytosis kinetics may be manipulated by the adequate substrate geometry, which opens up promising new leads of investigation in the study of synaptic processes.