Biological data transmission

Energy efficient hearing by enforced nanoscale calcium signaling

February 24, 2015

The hair cells of the inner ear can translate atomsize vibrations into electrical nerve impulses. Within the human body, they are a cell type with exceptional capabilities. By precisely coordinated biophysical processes, they manage to translate acoustic signals into electrical impulses that are then transmitted to the brain. In order to keep the brain at any time up-to-date, they are capable of releasing neurotransmitters at rates of up to 1000 events per second. With unprecedented precision, scientists at University Medical Center Göttingen, the Max Planck Institute for Dynamics and Self-Organization and the Bernstein Center Göttingen have examined the actual path lengths over which the important messenger calcium spreads inside the cell and identified the processes that keeps the messenger on course. The energy efficiency of the cells is maximized through short distances and the comprehensive capture of calcium ions that go astray. The new findings are published today in the journal PNAS (Proceedings of the National Academy of Sciences of The United States of America).

Combining experimental and mathematical cell research

In order to figure out what exactly happens in the hair cell of the ear during the release of neurotransmitters, the Göttingen research team led by professors Tobias Moser and Fred Wolf has combined genetic, cell biological, mathematical and computational methods.
The work was made possible by a triple-knockout mouse-developed by Professor Beat Schwaller-in which all essential calcium buffering proteins of the hair cells are genetically eliminated. Using this mouse, Tina Pangrsic and Nicola Strenzke at the University Medical Center Göttingen could evaluate for the first time changes in the transmitter release and the neural coding in the absence of calcium buffer. "By measuring the transmitter release of the cell, we noted that a lot more vesicles are released in the triple-knockout mouse," says Tina Pangrsic. The researchers demonstrated this by means of a technique developed by Erwin Neher in Göttingen, which allows precise measurements of the cell surface that increases by a tiny area every time a vesicle is released. "However, in the auditory nerve that receives the hair cells’ transmitters via synapses, this additional release is not detectable, the cells act completely normal," Nicola Strenzke adds. "Hence, an unnecessarily large machinery is set in motion inside the hair cell, and transmitters are released outside the synapse where they cannot fulfill their job."

Calcium takes the local route. Calcium ions need to travel only a one-molecule-scale distance to reach neurotransmitter containing vesicles and trigger release in auditory hair cells.

© Mantas Gabrielaitis

Calcium takes the local route. Calcium ions need to travel only a one-molecule-scale distance to reach neurotransmitter containing vesicles and trigger release in auditory hair cells.

© Mantas Gabrielaitis

The two Max Planck researchers Mantas Gabrielaitis and professor Fred Wolf developed a computer model that calculates the movements of calcium ions and the role of the calcium-binding proteins. "We wanted to know how the hair cells accomplish to concentrate the neurotransmitter release “command” at the right place in the cell," says Mantas Gabrielaitis. "We found that the calcium-binding proteins in hair cells help to focus the calcium signal at the synapse, hereby allowing for a transmission of the auditory stimuli to the brain with minimum energy cost."

The Göttingen researchers Moser and Wolf point out that with the results of their basic research “We can now understand better how the key sensory cells of the hearing sense “provide maximum performance without wasting energy.”