ic receptors initiate Ca2+ signalling via Gq, in contrast the 2 adrenergic and M2 and M4 muscarinic receptors regulate other signalling pathways via GI and another GTP binding protein, G0 (Fig. 2). Expression of such different receptor subtypes allows a single agonist to evoke unique responses in specific cells or tissues. Figure 1. G-Protein coupled receptor Figure 2. Ligated ion channel receptorIn the recent decade advances in scientific research have accomplished the art of cloning. Using these techniques in combination with radioligand binding and autoradiography, novel receptors have been identified and implemented using these molecular biological techniques. If a tissue or cell expresses more than a single subtype of receptor or when only insufficiently selective drugs are available identification of the specific signal that is generated by an individual receptor requires more direct approaches. These include expression of the cloned cDNA for the receptor in a well characterised cell where it’s signalling activities can be studied in detail, the expression and purification of the recombinant receptor for direct biochemical analysis of it’s functions, or the use of antisense strategies to evaluate which signal transducing pathway is necessary for agonist effects. Through the use of identification methods immuncytochemical staining western, northern and southern blots a immense amount of receptor subtypes have been discovered here are some of the findings for the glutamate receptor (Fig 4.) and the Classic neurotransmiters of the CNS (Fig 5.) Figure 4. A structured tree displaying the glutamate subunits with binding sites Figure 5 A structural tree of the Classical neurotransmitters and there receptor subtypesTo identify receptor subtypes in tissues a unique method has been ...
