Acetylcholine, carbachol, and GABA induce no detectable change in the length of isolated outer hair cells

Abstract

The mechanical and electrical properties of cochlear outer hair cells (OHCs) are suggested to modulate transduction by inner hair cells. These properties of OHCs are presumably regulated by efferent neurons which use several transmitters including acetylcholine (Ach) and gamma aminobutyric acid (GABA). Since it had been suggested that Ach causes isolated OHCs to shorten visibly, this study was designed to investigate whether GABA also alters the length of OHCs. OHCs were isolated from the guinea pig cochlea by mechanical dispersion after collagenase treatment. Cells were initially selected by strict morphological criteria. In addition they were only included in further studies if they attained a constant length during 10 min of superfusion with buffer solution. Neither GABA (20 μM; 100 μM), Ach (5 mM; 10 μM with 10 μM eserine) or carbachol (10 μM; 100 μM) altered OHC length when applied in iso-osmotic Hank's balanced salt solution (total number of cells tested, 72). If a change in length occurred it must have been smaller than 0.3 μm, our detection ability. In contrast, high potassium and variations in osmolarity changed hair cell length by 3–10% in agreement with other reports.