CHARACTERIZATION OF ENDOTHELIN RECEPTORS IN THE INNER MEDULLARY COLLECTING DUCT OF THE RAT

Endothelins may be important regulators of renal inner medullary collecting duct (IMCD) function. These peptides are secreted in large amounts by IMCD cells and can, in turn, potently inhibit sodium and water transport systems in the IMCD. This study characterized endothelin (ET) receptors in the IMCD in order to gain insight into this unique renal autocrine system. Radioligand binding studies with I-125-ET-1 yielded a B(max) of 205.7 fmol/mg and a K(D) of 218 pm for ET-1. Similar studies with I-125-ET-3 yielded two populations of receptors for ET-3, one with a K(D) of 50 pm and one with a K(D) of 920 pM. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of IMCD cells covalently labeling with I-125-ET-1 yielded two bands, one at 97 kDa with affinities of ET-1 greater-than-or-equal-to ET-2 >> ET-3 and one at 47 kDa with affinities ET-1 greater-than-or-equal-to ET-2 = ET-3. Reverse transcription and polymerase chain reaction revealed the presence of both endothelin receptor types A and B. These data indicate that IMCD cells have high affinity, high density receptors for endothelin and express both known types of endothelin receptor.