Biological data transmission
Energy efficient hearing by enforced nanoscale calcium signaling
Taking the short route: nanoscale calcium signaling at hair cell synapses
Sensory and nerve cells forward information through specialized cell junctions called synapses. Here, the information is transmitted by tiny packages (vesicles) containing neurotransmitter molecules that are released by one of the cells and that can be detected by the neighboring cell. The "sending" cell conveys the order to release the neurotransmitters by means of calcium ions. In its cell membrane, there are molecular "pores"—so-called ion channels—that sense the excitation of the cell and allow calcium ions to enter when a certain threshold is reached. In hair cells, these pores are the key translation device between the acoustic signals and the nerve impulses that are sent to the brain.
In order to fulfill its signal transmission mission, the calcium ions must quickly reach a sensor protein on the vesicles. The Max Planck researchers have calculated that this molecular sensor is located less than 20 nanometers (about 200 atomic diameters) from the ions entry point into the cell. Because they are randomly hit by the surrounding water molecules, it is physically inevitable that many of the entering ions move into wrong directions or overshoot the target location. Without special precautions these misguided ions could trigger the release of neurotransmitters outside the contact points—which would be wasteful as they would go undetected outside the synapse. Such a misplaced release would be a significant waste of energy as the vesicles and messengers must be expensively recycled after each release.
With their new results, the Göttingen researchers show that the hair cells in the inner ear use special calcium buffering proteins to capture ions that go astray. By means of a high concentration of three different calcium buffering proteins, the cells avoid the waste of energy.