The Role of the Mechanotransduction Ion Channel Candidate Nanchung-Inactive in Auditory Transduction in an Insect Ear

Insect auditory receivers provide an excellent comparative resource to understand general principles of auditory transduction, but analysis of the electrophysiological properties of the auditory neurons has been hampered by their tiny size and inaccessibility. Here we pioneer patch-clamp recordings from the auditory neurons of Müller-s Organ of the desert locustSchistocercagregariato characterise dendritic spikes, axonal spikes and the transduction current. We demonstrate that dendritic spikes, elicited by sound stimuli, trigger axonal spikes, and that both types are sodium- and voltage-dependent and blocked by TTX. Spontaneous discrete depolarisations summate upon acoustic stimulation to produce a graded transduction potential that in turn elicits the dendritic spikes. The transduction current of Group-III neurons of Müller-s Organ, which are broadly tuned to 3 kHz, is blocked by three ion channel blockers FM1-43, streptomycin and 2-APB known to block mechanotransduction channels. We investigated the contribution of the candidate mechanotransduction ion channel Nanchung-Inactive - which is expressed in Müller-s Organ - to the transduction current. A specific agonist of Nanchung-Inactive, pymetrozine, eliminates the sound-evoked transduction current while inducing a tonic depolarising current of comparable amplitude. The Nanchung-Inactive ion channels, therefore, have the required conductance to carry the entire transduction current, and sound stimulation appears not to open any additional channels. The application of three mechanotransduction ion channel blockers prevented the pymetrozine-induced depolarising current. This implies that either Nanchung-Inactive is, or forms part of, the mechanotransduction ion channel or it amplifies a relatively small current (<30 pA) produced by another mechanotransduction ion channel such as NompC. Significance Statement: The mechanically activated ion channel underpinning hearing is not known. We have pioneered intracellular patch-clamp recordings from locust auditory neurons to unravel the role of the candidate mechanotransduction ion channel Nanchung-Inactive in auditory transduction in insects.