AUTORADIOGRAPHIC LABELING OF P-2 PURINOCEPTORS IN THE GUINEA-PIG COCHLEA

Two different radioligands were used to identify extracellular ATP bin ding sites specific to P-2 purinoceptors in guinea-pig cochlear tissue . Deoxyadenosine 5'-(alpha-[S-35]thio)triphosphate ([S-35]dATP alpha S ; 10 nM) provided a high activity probe for the P-2y purinoceptor subt ype on the basis of selective block by 2-methylthio-ATP (2MeSATP; 100 mu M). [H-3]alpha, beta-methylene-ATP (10 nM), a high affinity probe f or a P-2x purinoceptor subtype was selectively blocked by inclusion of the related compound beta,gamma-methylene-ATP (100 mu M). Both probes labelled the organ of Corti, stria vascularis and spiral prominence r egions. The P-2x purinoceptor probe also bound to lateral wall tissue below the spiral prominence and insertion point of the basilar membran e within the scala tympani compartment, a region which failed to show significant binding using [S-35]dATP alpha S. Frozen sections of whole cochlea permitted analysis of radioligand binding to the cell body re gion (spiral ganglion in Rosenthal's canal) of the primary auditory af ferents and the auditory nerve itself, which lies within the central r egion of the modiolus of the cochlea. Both these regions exhibited 2Me SATP blockable [S-35]dATP alpha S binding whereas specific [H-3]alpha, beta-methylene-ATP binding was absent from spiral ganglion and minimal in the auditory nerve region. These results demonstrate a mixed P-2 p urinoceptor distribution in cochlear tissues and suggest that complex purine-mediated neurohumoral mechanisms may influence cochlear functio n at a number of sites.