NEGATIVE COOPERATIVITY IN THE HUMAN BRADYKININ B-2 RECEPTOR

A human kidney bradykinin (BH) B-2, receptor cDNA was transfected in C HO-KI cells to establish cell lines that express stably and at high de nsity a receptor exhibiting B-2, receptor properties in terms of coupl ing to cell signaling effecters, desensitization, and internalization. A cell line with a density of 1.3 x 10(6) receptors/cell allowed us t o carry out a detailed study of BK-receptor interaction over a wide ra nge of BK concentrations. A model assuming that BK binds to two recept or affinity states (depending on guanine nucleotide-sensitive coupling ) was not sufficient to account for the kinetics of EE binding. Equili brium kinetic analysis and studies of the effects of receptor occupanc y by agonists or antagonists on the kinetics of BH-receptor complex di ssociation revealed features typical of negative cooperative binding. The negative cooperativity phenomenon was also observed in isolated me mbranes in both the presence and absence of guanine nucleotide, Thus, following the interaction with Bg, B-2, receptor molecules likely inte ract with each other, resulting in an acceleration of bound ligand dis sociation and a decrease in the apparent affinity of the receptor for BR This phenomenon can participate in the desensitization process.