Second messenger systems

SECOND MESSENGERS SYSTEM

  • Many hormones, neurotransmitters, autacoids and drugs act on specific membrane receptors, the immediate consequence of which is activation of a cytoplasmic component of the receptor, which may be an enzyme such as adenylate cyclase, guanyl cyclase or activation of a transport system or opening of an ion channel.
  • These cytoplasmic components which carry forward the stimulus from the receptors are known as second messengers. The receptor itself is the first messenger.
  • Examples of second messengers are cAMP, cGMP, Ca2+, G-Proteins, IP3, DAG etc.
  •  cAMP serves as second messenger for adenosine, opioid, VIP, α2 and β adrenoceptors and H2 receptors.
  • cGMP serves as second messenger for angiotensin receptor.
  • IP3 and DAG serve as second messengers for α1 adrenoceptors, H1 receptors and cholecystokinin.
  • cAMP has varied regulatory effects on cellular functions, for example, energy metabolism, cell division and cell differentiation, ion-transport, ion-channel funtion, smooth muscle contractility etc.
  • cGMP has ben identified in cardiac cells, bronchial smooth muscle cells and other tissues. For most effects produced cAMP seems to be stimulatory while cGMP seems to be inhibitory in nature. When the cAMP and cGMP systems are bothe present in a single cell or tissue, they are linked to receptors through which drugs produce opposite effects.
  • IP3 and DAG are degradation products of membrane phospholipid by the enzyme phospholipase C.
Last modified: Wednesday, 25 April 2012, 7:09 AM