Evoking and Resolving Quantal Neurotransmitter Release on a Microchip

Abstract

A microchip that facilitates in-vitro electrical and electrochemical measurements of individual cells and cell clusters was fabricated using surface micromachining and thick film technologies. In the present study, the device was applied towards the detection of exocytotic events from electrically stimulated rat pheochromocytoma (PC12) cells. Using device microfluidics, cells were positioned in a recording chamber over a 5 μm × 10 μm gold working electrode (WE). Channel dimensions (10 μm deep × 10 μm wide) ensured a tight fit for the ∼12 μm diameter PC12 cells in the chamber resulting in direct contact of the cells with the WE. This proximity allowed for quantal resolution of catecholamine release events from the cells and corresponding analysis of release kinetics and quantal size. Cells were stimulated through the application of sinusoidal voltage waveforms across axially-positioned, extracellular electrodes. In this manner, patterned extracellular gradients were generated across the cell thereby resulting in membrane depolarization. To facilitate interpretation of the stimulating electric field in relation to the cell and subsequent dopamine release, quasi-static electromagnetic FEM models were generated using COMSOL Multiphysics software. Upon depolarization, simultaneous chronoamperometric recordings at the WE confirmed stimulus-triggered dopamine release from the cells with a small subset of cells exhibiting release that modulated with the depolarizing cycle of the sinusoidal stimulus. It is anticipated that such a chip could provide a semi-automated alternative to the conventional, labor-intensive carbon fiber electrode (CFE) approach to neurotransmitter measurement.This work was supported in part by the National Institutes of Health, NIDCD R01 DC04928 and by National Science Foundation, IGERT NSF DGE-9987616.