Aging does not alter phosphoinositide hydrolysis in the rat cochlear lateral wall

We have previously reported that the inositol 1,4,5-trisphosphate (InsP3) second messenger system is coupled to purinergic P2y receptors in the cochlear sensory epithelium and lateral wall. The tissues of the cochlear lateral wall (stria vascularis and spiral ligament) are responsible for maintaining the ionic composition of the cochlear endolymph. Both the endolymphatic potential and signal transduction processes are well known to be affected by aging. Furthermore, intracellular inositol concentrations decrease with age in the cochlear sensory epithelia. The present study compared the purinergic receptor-mediated release of inositol phosphates (InsPs) in the cochlear lateral wall of young (3 month-old) and aged (24 month-old) Fischer-344 rats. No differences were found in the incorporation of mnyo-[3H]inositol into phosphoinositide lipids. Likewise, the purinergic receptor-mediated release of InsPs remained unchanged. This suggests that the InsPs second messenger system in the cochlear lateral wall, in contrast to the sensory epithelium, may not be affected by aging.