Temperature-dependent negative cooperativity among angiotensin II receptors of isolated rat glomeruli

The binding characteristics of angiotensin II to isolated rat glomeruli were studied at various temperatures from 15 to 37 degrees C using 125I-labeled angiotensin II. The remarkable features of the binding at 37 degrees C, compared with those at lower temperatures, were (1) decreased maximal binding due to increased dissociation rate, (2) short duration of the steady state, which was, however, sufficient for performing steady-state binding assays, and (3) marked curvilinear Scatchard plots with upward concavity. The difference between the dissociation rates caused by dilution only and by dilution plus cold angiotensin II increased with increase in temperature. From these results, we conclude that the site-site interactions of a negatively cooperative type, which are negligible at lower temperatures, exist among rat glomerular angiotensin II receptors at the physiological temperature, and that the binding study may as well be performed at 37 degrees C for the purpose of investigating quantitative correlation between the hormone binding and its biological effect.