Microinjection Technique for Assessment of Gap Junction Function

Visualization and quantification of dynamic intercellular coupling in human embryonic stem cells using single cell sonoporation

Gap junctions (GJs), which are proteinaceous channels, couple adjacent cells by permitting direct exchange of intracellular molecules with low molecular weights. GJ intercellular communication (GJIC) plays a critical role in regulating behaviors of human embryonic stem cells (hESCs), affecting their proliferation and differentiation. Here we report a novel use of sonoporation that enables single cell intracellular dye loading and dynamic visualization/quantification of GJIC in hESC colonies. By applying a short ultrasound pulse to excite single microbubbles tethered to cell membranes, a transient pore on the cell membrane (sonoporation) is generated which allows intracellular loading of dye molecules and influx of Ca²⁺ into single hESCs. We employ live imaging for continuous visualization of intercellular dye transfer and Ca²⁺ diffusion in hESC colonies. We quantify cell–cell permeability based on dye diffusion using mass transport models. Our results reveal heterogeneous intercellular connectivity and a variety of spatiotemporal characteristics of intercellular Ca²⁺ waves in hESC colonies induced by sonoporation of single cells.

Intracellular delivery of colloids: Past and future contributions from microinjection

The manipulation of single cells and whole tissues has been possible since the early 70's, when semi-automatic injectors were developed. Since then, microinjection has been used to introduce an ever-expanding range of colloids of up to 1000 nm in size into living cells. Besides injecting nucleic acids to study transfection mechanisms, numerous cellular pathways have been unraveled through the introduction of recombinant proteins and blocking antibodies. The injection of nanoparticles has also become popular in recent years to investigate toxicity mechanisms and intracellular transport, and to conceive semi-synthetic cells containing artificial organelles. This article reviews colloidal systems such as proteins, nucleic acids and nanoparticles that have been injected into cells for different research aims, and discusses the scientific advances achieved through them. The colloids' intracellular processing and ultimate fate are also examined from a drug delivery perspective with an emphasis on the differences observed for endocytosed versus microinjected material.