Shape changes in isolated outer hair cells: measurements with attached microspheres

Area of Science:

• Cell biology
• Biophysics
• Auditory science

Background:

• Outer hair cells (OHCs) exhibit shape changes in response to stimuli.
• Quantifying localized OHC shape changes is crucial for understanding motility mechanisms.
• Lack of fixed internal landmarks hinders precise segmental analysis of OHC shape changes.

Purpose of the Study:

• To develop a method for analyzing localized shape changes in isolated outer hair cells.
• To investigate differential segmental length changes in OHCs under various stimuli.
• To identify the location of the contractile apparatus within outer hair cells.

Main Methods:

• Digitized video-imaging of isolated outer hair cells.
• Attachment of microspheres to serve as fixed reference points on the cell body.
• Induction of cellular shape changes via K(+)-depolarization and intracellular Ca(2+) elevation.
• Quantitative analysis of length changes in basal, middle, and apical segments of the OHC.

Main Results:

• K(+)-depolarization induced significant shortening in the middle segment (14 +/- 6%) compared to basal (10 +/- 5%) and apical (7 +/- 6%) sections.
• Cortical contractions via elevated intracellular Ca(2+) led to more pronounced elongation in the basal (8 +/- 2%) than apical (6 +/- 2%) or middle (6 +/- 3%) regions.
• Microsphere reference points allowed for accurate, localized measurement of OHC shape dynamics.

Conclusions:

• Microspheres provide a reliable method for analyzing localized outer hair cell shape changes.
• OHCs exhibit distinct segmental responses to different stimuli, indicating specific contractile mechanisms.
• This technique offers further insight into the biophysical basis of outer hair cell motility.