Localisation of [3H]clonidine binding to membranes from guinea pig renal tubules.

The selective radioligand [3H]clonidine has been used to localise alhpa 2 adrenoceptors in guinea pig kidney. Chemical sympathectomy with 6-hydroxydopamine produced no significant change in the number of sites labeled by [3H]clonidine indicating that the majority of binding sites were not located on sympathetic nerve terminals. Binding was enhanced in membranes prepared from renal tubules and considerably reduced in preparations from glomeruli. Subcellular fractions of renal cortex revealed that binding was to plasma membranes and that the greatest binding capacity was present in the fraction rich in basal lateral membranes. It is concluded that the major concentration of renal alpha 2 adrenoceptors are present on renal tubules and that they may be localised to a particular pole of the renal tubule cell.