Cloning and characterization of a novel endothelin receptor from Xenopus heart

Endothelin (ET) receptors display subtype heterogeneity and so far three subtypes of ET receptors, namely ETA, ETB, and ETC, have been identified, cloned, sequenced, and characterized. Based on the binding profile of ET and related peptides, a novel ET receptor (ETAX) was identified in the follicular membranes of Xenopus laevis oocytes (Kumar, C. S., Nuthulaganti, P., Pullen, M., and Nambi, P. (1993). Mol. Pharmacol. 44, 153-157). Here we report the cloning and characterization of this ETAX subtype from X. laevis heart. A cDNA was isolated that encodes a protein of 415 amino acids that shares 74, 60, and 51% identities with human ETA, human ETB, and Xenopus ETC receptors, respectively. Competition binding studies of the cloned receptor expressed in COS cells using ET-related peptides suggested that this receptor is pharmacologically identical to that expressed in Xenopus oocyte follicular, heart, and lung membranes. Phosphoinositide turnover and oocyte electrophysiological studies indicated that the cloned receptor is functionally coupled to a second messenger system.