IDENTIFICATION OF ALPHA(1)-ADRENOCEPTOR SUBTYPES IN RAT RENAL PROXIMAL TUBULES

Although the existence of alpha(1)-adrenoceptor subtypes has been sugg ested in the kidney, their characterization in the proximal tubules ha s not been reported. This study was undertaken to characterize the alp ha(1)-adrenoceptor subtypes in the renal proximal tubules. [H-3]Prazos in bound to proximal tubules with a K-D of 106+/-17 pM and a B-max of 152+/-9 fmol/mg protein. Pretreatment of the tubules with chloroethylc lonidine, 100 mu M, reduced the B-max of [H-3]prazosin binding by abou t 50%, indicating the presence of the alpha(1B)-adrenoceptor subtype. Competition studies performed with the alpha-adrenoceptor antagonists, WB 4101, (+)-niguldipine, 5-methylurapidil and phentolamine were shal low and could be distinguished into a high affinity (alpha(1A)) and a low affinity site (alpha(1B)) with an approximately equal distribution of both receptor subtypes. These observations clearly demonstrate the existence of alpha(1A)- and alpha(1B)-adrenoceptor subtypes in the re nal proximal tubules.