Like the M 1 and M 3 muscarinic receptor, M 5 receptors are coupled with G proteins of class Gq that upregulate phospholipase C and, therefore, inositol trisphosphate and intracellular calcium as a signaling pathway.
Radioactive iodine is a very effective type of treatment for cancer of the thyroid gland. Thyroid cells absorb iodine. The radioactive iodine from the drink or capsule is absorbed into your body and picked up by the thyroid cancer cells wherever they are. So it can kill the cancer cells even if they have spread.
Radioactive iodine (commonly called radioiodine) is a form of iodine chemically identical to nonradioactive iodine. Therefore, the thyroid gland, which takes up iodine to make thyroid hormone, cannot distinguish between the two. However, the nucleus of a radioactive iodine molecule has excess energy and gives off radiation that can have effects on the cells in which it is concentrated.