January 8, 2013
Hearing Mechanism Resembles Operation Of Car Battery: Study
redOrbit Staff & Wire Reports - Your Universe Online
One of the mechanisms involved in human hearing is similar to the operation of a car battery, according to a new study by researchers at the University of Iowa (UI).
The scientists conducted their study using fruit flies, whose hearing mechanisms resemble that of humans.
Specifically, the flies´ auditory system contains a protein that functions as a sodium/potassium pump, and is highly expressed in a specialized support cell called the scolopale cell. This cell is important because it wraps around the sensory endings in the fly´s ear, forming a tight extra-cellular compartment around them known as the scolopale space.
“You could think of these compartments as similar to the compartments of a battery that need to be charged up so they can drive electrons through circuits,” said University of Iowa biologist Daniel Eberl, the study´s lead researcher.
“In the auditory system, the charge in the scolopale space drives ions, or electrically charged atoms, through membrane channels in the sensory endings that open briefly in response to activation by sounds.”
“Our work shows that the sodium pump plays a particularly important role in this cell to help replenish or recharge this compartment with the right ions. The human ear also relies on a compartment called the scala media, which similarly drives ions into the sensory cells of the ear,” he said.
The scientists utilized something known as the fruit fly ℠love song,´ a sound generated by a vibrating wing. This ℠love song´ stimulates a fly to move whenever a sound is emitted and received, so the researchers used it to test whether or not electrical recharging was taking place in the fly´s ear.
“In these experiments we tested the fly's hearing by inserting tiny electrodes in the fly's antenna, then measuring the electrical responses when we play back computer-generated love songs,” Eberl said.
Since there are many similarities between fruit fly and human mechanisms of hearing, using a fly model to identify additional new components required for generating the correct ion balance in the ear will broaden our understanding of the human hearing process as well, Eberl explained.
“The sodium pump is highly expressed in scolopale cells where it is thought to help maintain ion homeostasis, which is critical for auditory transduction,” the researchers wrote in a paper about the study.
“Loss of sodium pump function results in hearing loss.”
“The study´s experimental system could be used to elucidate additional mediators of ion transport and fluid regulation in the inner ear.”
Eberl and colleagues´ report, entitled "Cell-type-specific roles of Na+/K+ ATPase subunits in Drosophila auditory mechanosensation,” is published in the current issue of the journal Proceedings of the National Academy of Sciences.