Cross reactivity among the ligands of the 7 helix family.

"Specific" drugs for receptors of the 7 helix family inhibited in high doses other receptors of the same family, as well. Atropine inhibited [3-H]-clonidine binding, beta-adrenergic drugs: propranolol, betoxalol, ICI 118.551 inhibited labelled QNB binding to all the 3 main subtypes of muscarinic receptors. Authors propose the existence of common features in the ligand binding sites of the receptors of 7 helix family.