Effects of SERCA and PMCA inhibitors on the survival of rat cochlear hair cells during ischemia in vitro.

An important mechanism underlying cochlear hair cell (HC) susceptibility to hypoxia/ischemia is the influx of Ca(2+). Two main ATP-dependent mechanisms contribute to maintaining low Ca(2+) levels: uptake of Ca(2+) into intracellular stores via smooth endoplasmic reticulum calcium ATPase (SERCA) and extrusion of Ca(2+) via plasma membrane calcium ATPase (PMCA). The effects of the SERCA inhibitors thapsigargin (10 nM-10 microM) and cyclopiazonic acid (CPA; 10-50 microM) and of the PMCA blockers eosin (1.5-10 microM) and o-vanadate (1-5 mM) on inner and outer hair cells (IHCs/OHCs) were examined in normoxia and ischemia using an in vitro model of the newborn rat cochlea. Exposure of the cultures to ischemia resulted in a significant loss of HCs. Thapsigargin and CPA had no effect. Eosin decreased the numbers of IHCs and OHCs by up to 25 % in normoxia and significantly aggravated the ischemia-induced damage to IHCs at 5 and 10 microM and to OHCs at 10 microM. o-Vanadate had no effect on IHC and OHC counts in normoxia, but aggravated the ischemia-induced HC loss in a dose-dependent manner. The effects of eosin and o-vanadate indicate that PMCA has an important role to play in protecting the HCs from ischemic cell death.