STRUCTURAL AND ULTRASTRUCTURAL ASPECTS OF ISOLATED IMMATURE COCHLEAR OUTER HAIR-CELLS MAINTAINED IN SHORT-TERM CULTURE

Immature outer hair cells (OHCs), isolated from developing rat cochlea without using proteolytic enzymes, were maintained in short-term cult ure in a clot of coagulated plasma. Cell viability was assessed by a l aser scanning image cytometer, using double-fluorescent labeling. Ligh t and transmission electron microscopy was used to study the morpholog y of isolated cells. Ten to 60 healthy OHCs were obtained from one coc hlea, either as single isolated cells or clusters containing 2-10 cell s from the same row. Although dead cells were observed only 1 h after dissociation, there were still viable cells after 6 h. Isolated OHCs w ere not perfectly cylindrical, due to the immaturity of their cortical structures. One hour after dissociation the ultrastructural organizat ion of the isolated cells was generally well preserved, but this was f ollowed by dilatation of the Golgi apparatus and endoplasmic reticulum . Specific changes in isolated OHCs were also observed at the subsurfa ce cistemae and cuticular plate. Although degenerating OHCs generally showed a classic pattern of necrosis, certain morphological features r eminiscent of apoptosis were also observed. This study emphasises the difficulty involved in investigating isolated immature OHCs in vitro a nd provides a basis for future research into the physiological require ments of isolated immature OHCs.