Acoustic stimulation increases phosphoinositide breakdown in the guinea pig cochlea

The effect of sound stimulation on phosphoinositide turnover was investigated in the inner ear of the guinea pig. The perilymphatic spaces of the cochlea were perfused with [(32)P]orthophosphate ((32)P(i)) and labeled lipids analyzed in the tissues of the lateral wall of the cochlea (stria vascularis and spiral ligament) and the basilar membrane (organ of Corti). Consistent with previous results, polyphosphoinositides rapidly incorporated (32)P(i) comprising 70-80% of labeled lipids in all tissues analyzed: phosphatidylinositol 4,5-bisphosphate (PtdInsP(2)) was 66% of total [(32)P]phospholipids in the lateral wall tissues and 45% in the organ of Corti; phosphatidylinositol 4-phosphate (PtdInsP) was 28% in the lateral wall and 24% in the organ of Corti. After 90 min of labeling the hydrolysis of lipids was measured by replacing the radioactive P(i) with 1 mM NaH(2)PO(4) in the perfusate for the 30 min "chase". Exposure of the ear to sound (100 dB white noise) during the chase significantly augmented the hydrolysis of [(32)P]PtdInsP(2) in the organ of Corti by 20% (P = 0.01) but not in the lateral wall tissues. Since the organ of Corti contains the auditory sensory cells, the results suggest that the observed increased hydrolysis of PtdInsP(2) is associated with auditory processing in the inner ear.