Study shows different cell response offers more control to muscles

Slight variations in individual muscle cell contractions enable the whole muscle to bend with more precision and control.

Cells’ responses to electrical shocks are measured as the amount of calcium ions that pass through their membranes (left). Each cell’s response to the stimulation was different, but its unique response was consistent every time it was shocked (center). Researchers state that an individual cell’s response is accurate, represented by the very small black error bars (right). Image Credit: © 2020 Shinya Kuroda.

Now, experts suspect that biological systems, which were historically dismissed as error or “noise,” could have evolved to include inevitable difference as a form of information in their communication channels. A group of experts from the University of Tokyo published the study results in Cell Reports, a scientific journal.

The differences between cells’ responses to stimulation is actually another form of information.”

Shinya Kuroda, Study Co-Author and Professor, Graduate School of Science, University of Tokyo

Kuroda is also the leader of the research laboratory that conducted the experiments at the University of Tokyo.

While robots could be developed to react identically together, every cell in a natural system comprises all manner of peculiarities—for example, exclusive patterns of gene expression. Within a muscle, every cell receives the same kind of nerve signal to relax or contract; however, one specific cell might react with a powerful contraction, whereas its neighbor reacts with a feeble contraction.

The scientific community has already suspected that such differences were induced by information being lost along the communication channel.

In their latest experiments, the team from the University of Tokyo tracked the contractions of 551 individual mouse muscle cells cultured in laboratory dishes, giving 200 tiny electrical shocks to each cell to observe the response of different cells to the same stimulation.

Previously, no one had the technical ability to do these repeated measurements of single cells.”

Takumi Wada, Study First Author and Project Research Associate, University of Tokyo

Irrespective of whether a cell reacted weakly or strongly to a specific stimulation, all cells reacted with a greater response upon receiving a greater electrical shock. Furthermore, individual cells were also consistent; a cell responded in the same way whenever it received the same shock stimulation.

We observed that each cell is quite good at responding to the stimulation accurately. They are simply different.”

Shinya Kuroda, Study Co-Author and Professor, Graduate School of Science, University of Tokyo

Precise and consistent responses to every level of stimulation ensure that differences in cells stay consistent and thus meaningful, instead of chaotic and unpredictable. Cell-to-cell variation implied that, as a whole, the muscle tissue can identify a broader range of stimulation intensities and can react with a corresponding broader range of control. If every cell reacted identically, the entire muscle tissue could only execute on/off binary responses.

Using single fibers of mouse skeletal muscle, the researchers conducted more experiments and also examined the recordings of facial muscle activity that is routinely obtained while performing surgeries on human patients.

This idea of individual cell variability, transmitting the crucial information via biological systems, may also be applicable to other processes, wherein life needs a broad spectrum of responses, including hormone secretion.

For instance, the pancreas may be able to discharge different quantities of insulin hormone because individual beta cells of this organ would be reacting differently to blood sugar levels.