Comparison of the kinetics and extent of muscarinic M1-M5receptor internalization recycling and downregulation in Chinese Hamster Ovary cells

摘要

We characterized agonist-induced internalization, recycling and downregulation of each muscarinic receptor subtype (M1 – M5) stably expressed in Chinese hamster ovary (CHO) cells. The radioligands [³H]QNB and [³H]NMS were used to measure the total and plasma membrane populations of muscarinic receptors, respectively. Following carbachol treatment (1 mM), the rank orders for the rate of carbachol-induced internalization of the muscarinic subtypes were M2 > M4 = M5 > M3 = M1, respectively. Unlike the M2 receptor, M1, M3, M4 and M5 receptors recycled back to the plasma membrane after one-hour carbachol treatment. The receptor downregulation elicited to 24-hour carbachol treatment was similar for M2, M3, M4 and M5 receptors, whereas that for the M₁ receptor was greater. Our results indicate that there are subtype-specific differences in the rate and extent of agonist-induced muscarinic receptor internalization, recycling and downregulation in CHO cells.