Competitive Interceptors

To understand the effects of agonists and competitive antagonists the receptors involved must be identified first. There are 2 major groups of receptors present in rat ileum, the first being 5-hydroxytryptamine (5-HT) receptors and the second, muscarinic acetylcholine receptors (mAChR) – and of these two groups there are certain subtypes in the ileum contributing to its tone, motility, secretion and blood flow. The 5-HT receptor subtypes most prevalent in the rat ileum were, 5-HT2A, 5-HT2B, 5-HT3 and some activity from 5-HT4 (Briejer, Mathis and Schuurkes, 1997) 5-HT2A, 5-HT2B and 5-HT4 are all G protein coupled receptors (GPCR), however 5-HT2A and 5-HT2B are coupled to a Gq protein that is responsible for increasing levels of inositol triphosphate (IP3) and cytosolic calcium (Hoyer, Hannon and Martin, 2002), both of these acting a second messenger systems. 5-HT4 is coupled to a Gs protein receptor that increases cyclic adenosine monophosphate (cAMP) (Hoyer, Hannon and Martin, 2002), which acts as a second messenger. The second messengers lead to further configuration changes and are responsible for …show more content…
Depending on the amount of 5-HT released either by EC cells, or directly applied to the organ, as in this experiment, determines level of response from the receptors (Coates et al., 2006). Little agonist and it may not be able to activate a receptor (or enough receptors for a response), and too much can lead to certain disorders and irritability. Serotonin-selective reuptake transporters (SERTs) act to inhibit the action of 5-HT by removing it from the interstitial space where it may then bind (Effects of serotonin transporter inhibition on gastrointestinal motility and colonic sensitivity in the mouse). The second messengers activated on the ileum by 5-HT is dependent on the receptors activated as listed above – excluding 5-HT3, which has a direct