(Invited) Electrochemical Induction of Insulin Secretion from Cultured Pancreatic β Cells
Authors: Funabashi Hisakage 
Published: December 2024

Recently, various methods have been developed to create functional cells through cell cultivation techniques, particularly with the utilization of embryonic stem (ES) cells or induced pluripotent stem (iPS) cells. These methodologies have unlocked the potential to produce promising applications across various fields, including regenerative medicine, disease modeling, and drug discovery. Furthermore, methodologies for engineering cell aggregates that exhibit specific functions, known as organoids, are paving the way for innovative biomedical applications. As such, there is a need for methodologies that enable precise control over cellular functions, allowing researchers to manipulate cell behavior in a desired manner. Addressing this need, the present study aimed to develop a method for manipulating cell functions through easily controllable ON/OFF regulation using electrochemical operations. In this study, secretion function, which is a representative function of cellular activities involving changes in cellular membrane potential, was focused on as a cellular function. Specifically, the insulin secretion of pancreatic β cells was targeted as a concrete model.
Insulin, a pivotal endocrine hormone synthesized and secreted by pancreatic β cells, plays a critical role in glucose homeostasis. The secretion of insulin by pancreatic β cells is tightly regulated in response to blood glucose concentration. Within pancreatic β cells, glucose uptake via Glucose transporter initiates glycolysis and the citric acid cycle, leading to ATP production. As the intracellular ATP level increases, ATP-sensitive potassium ion channels on the cell membrane close. This event prevents the efflux of potassium ions. Consequently, membrane potential increases and the voltage-dependent calcium ion channels on the cell membrane open, allowing calcium ions to flow into the cell. This influx of calcium ions becomes a trigger signal for insulin secretion, inducing insulin release via endocytosis. Considering this mechanism, it was hypothesized that the electrochemical control of the membrane potential could manipulate the function of pancreatic β cells artificially, specifically insulin secretion.
To test this hypothesis, an original cell culture device was created by attaching acrylic rings to transparent electrodes, allowing the cultivation, observation and electrochemical stimulation of cells on electrodes. When iGL cells (a pancreatic β cell line expressing a fusion protein of insulin and a bioluminescent protein, available from Cosmo Bio, Japan) were cultured in this cell culture device, they exhibited proliferation, thus confirming the feasibility of further experiments based on live cell imaging. Next, the response of iGL cells cultured in the device to electrochemical stimulation was monitored using bioluminescent live cell imaging. The electrical stimulation by applying a potential to the electrode was performed using a three-electrode system. In the beginning, iGL cells exhibited bright bioluminescence. However, upon the application of the potential to the electrode, the cells immediately became dark. Subsequently, the bioluminescent intensities of the culture medium collected before and after electrochemical stimulation were compared. As a result, it was observed that the medium collected after the electrochemical stimulation exhibited a brighter intensity, indicating higher concentration of fusion proteins of insulin and the bioluminescent protein. Additionally, morphological analyses showed no significant changes in cell morphology during the stimulation process. This finding confirmed that the decrease in bioluminescence observed in the cellular response to electrochemical stimulation was attributable to the secretion of the fusion protein of insulin and the bioluminescent protein from the cells into the culture medium.
Based on these observations, it was concluded that insulin secretion from the cells on the electrode was electrochemically induced by applying a potential. While further analysis of the mechanisms is necessary, it is expected to develop a novel living cellular device whose function is regulated by electrochemical methods that can easily linked to current electronic devices.