Fatal contractions: ultrastructural and electromechanical changes in outer hair cells following transmembraneous electrical stimulation.

A form of outer hair cell vulnerability was examined as related to cellular structure. Electrically-induced somatic displacements on the order of 500 nm (peak-to-peak) were accompanied by a superimposed slow tonic contraction in cell length. Shortening by as much as 22% of the initial cell length was seen to occur at rates of 100 nm/s. Such changes often resulted in increased detection thresholds as well as a reduction in asymmetry of the frequency-following motile response component. The tonic contractions were non-reversible. Solitary cells were recovered following transmembraneous electrical stimulation in order to examine possible structural changes associated with the contractions. In a number of well-preserved controls, multiple flattened non-fenestrated cisternae were found lining the cytoplasmic compartment. In contrast, cells which underwent tonic shortening invariably possessed fragmented membraneous cisternae resembling those typically seen in whole-organ preparations. The degree of fenestration corresponded to the extent of cell shortening. These findings suggest that the so-called 'fenestrated' subsurface cisternae, previously thought to be a normal anatomical component of the outer hair cell, may be the remnant of a highly organized structure in vivo. The potential role of the cisternal system as a force generating substrate is discussed.