P2-PURINOCEPTORS STIMULATE INOSITOL PHOSPHATE RELEASE IN THE ORGAN OF CORTI

WE examined the effects of purinoceptor agonists on inositol phosphate (IP) release in the guinea-pig organ of Corti. The P2y receptor agonist ATP-gamma-S (200-mu-M) increased IPs 4-fold; identical concentrations of alpha,beta-methylene ATP, a P2x agonist, and adenosine, a P1 agonist, did not significantly affect IP release. In calcium-free incubations, simulated IP release decreased by 35% indicating partial dependence of ATP-mediated phosphoinositide hydrolysis on calcium influx. ATP-stimulated IP release was not enhanced by the cholinergic agonist carbachol known to increase IPs via muscarinic receptors in the organ of Corti. This is consistent with the notion that ATP and carbachol have a common target, most likely outer hair cells. P2 purinoceptors coupled to the phosphoinositide cascade suggest ATP as an afferent neuromodulator or efferent neurotransmitter in the cochlea.