K+ pump: from caterpillar midgut to human cochlea

Area of Science:

• Sensory Physiology
• Molecular Biology
• Auditory Neuroscience

Background:

• Deafness, affecting millions, is linked to mutations in genes like H(+) V-ATPase subunit B(1).
• The precise ionic mechanisms enabling high-frequency (20 kHz) sound transduction remain poorly understood.
• Maintaining constant endocochlear potential (EP) and ion concentrations (Ca2+, H+, K+) is vital for auditory signaling.

Purpose of the Study:

• To elucidate the ionic flows responsible for high-frequency sound transduction.
• To propose a novel hypothesis explaining the generation of the endocochlear potential (EP).
• To integrate known and new evidence into a cohesive model of auditory signaling.

Main Methods:

• Hypothesized a novel model involving H(+) V-ATPase and K(+)/H(+) antiporter (KHA) for ion cycling.
• Utilized immunolocalization of KHA2 in stereocilial membranes.
• Incorporated mass spectroscopy data of V-ATPase subunits in isolated chicken stereocilia.

Main Results:

• The proposed model suggests rapid (∼10 μs) cycling of Ca2+, H+, and K+ across stereocilial membranes.
• This rapid cycling is sufficient to explain the fast kinetics required for 20 kHz signaling.
• Evidence supports the presence of KHA in the membrane, coupled with H(+) V-ATPase.

Conclusions:

• A novel 'Type V' pump, comprising an electrogenic H(+) V-ATPase and an electrophoretic KHA, generates the EP.
• This mechanism provides a viable explanation for rapid ion transport necessary for high-frequency hearing.
• The model offers a potential paradigm shift in understanding sensory physiology and auditory signal transduction.