Development of a microfluidic cell culture and monitoring system for intracellular signaling studies

We describe a microfluidic cell culture and monitoring system that temporally controls molecule concentrations around cells cultured in a small space. The simple system consists of three syringe pumps and a microfluidic device with two inlet ports and two outlet ports. Each syringe pump discharges or draws culture medium, solutions containing signal molecules, or cell suspensions through a port in a programmed flow rate sequence. Signal molecule solutions of differing concentration are merged in a microchannel, mixed immediately, and transported into the cell culture chamber. Regulating the flow rate ratio of syringe pumps over time enables dynamic control of the concentration of signal molecules in the cell culture chamber. The system provides various time-dependent waveforms of concentration over cultured cells, including pulse, rectangular, and triangular. The practical performance of the system for concentration control was evaluated using fluorescent dye imaging. The system was also used with CHO-K1 cells to measure intracellular Ca2+ concentrations, which vary with extracellular ATP levels. When a rectangular pulse of ATP was applied to the cells, Ca2+ levels increased quickly. By contrast, several Ca2+ peaks were observed in response to stepwise increases in ATP concentration. Single-cell Ca2+ responses to ATP pulse stimulation were analyzed by quantitative fluorescence imaging. Hierarchical clustering and quantitative analysis of single-cell data revealed the diversity of Ca2+ responses to ATP pulse stimulation. These results demonstrate that the microfluidic cell culture system is useful for studying a variety of cellular responses, including cell signaling.