Identification of muscarinic receptors in lung of guinea pig

Using radioligand binding assay, muscarinic receptors in the lung tissue of guinea pigs were identified. Two components with higher affinity/low binding capacity and lower affinity/high binding capacity have been revealed. The binding of [3H]QNB to the 2 components was decreased when the membranes were preincubated with N-ethylmaleimide (NEM). However, a decreased binding can only be screened in the component with higher binding capacity (BH) when the membranes were preincubated with dithiothreitol (DTT). The results suggest that the difference in affinity between the 2 components may be a reflection of the existence of 2 different kinds of binding sites.