Ipratropium is an anticholinergic drug used to control and prevent symptoms of chronic obstructive pulmonary disease (COPD) such as wheezing and shortness of breath. It can also be used for asthma or any pulmonary disease that can be relieved by opening of the bronchial airway. It is inhaled where it can immediately enter the lungs and act on the smooth muscles. Ipratropium inhibits the M1, M2, and M3 muscarinic acetylcholine receptors. These receptors are coupled to the Gq cascade which is being prevented by Ipratropium. The inhibition of the Gq cascade prevents the acitvation of phospholipase C, which would convert Phosphatidylinositol (3,4,5)-trisphosphate to inositol (3,4,5)-trisphosphate (IP3) and diacylglycerol (DAG). IP3 would then activate IP3 receptors on the sarcoplasmic reticulum leading to the release of stored calcium into the cytosol. the muscarinic acetylcholine receptors being inhibited prevents calcium from entering the cell which means calcium does not readily bind to calmodulin, and calmodulin isn't present to activate myosin light chain kinase. Since myosine light chain kinase is not activated, Serine/threonine-protein phosphatase continues to dephosphorylate myosin LC-P, and more cannot be synthesized so myosin remains unbound from actin causing muscle relaxation. This relaxation of the smooth muscles in the lungs causes the bronchial airways to relax which causes bronchodialation, making it easier to breathe.

Ipratropium M3 Bronchodilation Pathway References