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.
Recommended reading: Breast Cancer and Iodine : How to Prevent and How to Survive Breast Cancer Dr. David Derry (Link to Amazon.com) - This book is about the cause, prevention and treatment of breast cancer. Breast cancer has two phases. The first one, from abnormal cells up to carcinoma in situ reverses with iodine.