Abstract
An increase of intracellular cyclic AMP levels induced by 1-isoprenaline (1-Iso) was significantly depressed in coexistence with BuTMA or histamine, but not with KCl or BaCl2. An analysis of steady state data for d, l-[3H]-isoprenaline binding to single cells of taenia from guinea pig caecum in the presence of histamine or KCl by Scatchard plots was performed. The affinity of 1-Iso for β-adrenoceptor sites was decreased in the presence of histamine but not in the presence of KCl. These results suggest that the interaction of 1-Iso with the β-adrenoceptors is interfered with by histamine and butyltrimethylammonium, for which the specific receptors were postulated, but not with KCl and BaCl2, nonspecific smooth muscic stimulants. These phenomena demonstrate the heterotropic negative cooperativity among the heterogeneous receptors.
