Christian Bruns

Somatostatin Receptor Gene Family - Subtype Selectivity for Ligand Binding

Somatostatin (SST; SRIF somatotrophin release inhibiting factor) produced by neuronal‚ neuroendocrine‚ inflammatory‚ immune cells and tumours‚ regulates its many (patho)-physiological functions through specific cell membrane receptors. Five different SST receptors have been identified and classified respectively. Based on pharmacological features and molecular cloning‚ they are separated into two families‚ and They all belong to the superfamily of G-protein coupled receptors with seven transmembrane spanning domains (Hoyer et al.‚ 1994). These receptors have high affinity for the naturally occurring peptides‚ SST-14 and SST-28‚ but also for the related cortistatin (CST) peptides (rCST-14‚ hCST-17 and CST-29) which are specifically produced in the brain. Whether there are specific CST receptors is presently unknown‚ therefore this chapter will generally refer to SST receptors. Activation of SST receptors inhibits adenylyl cyclase and regulates a number of signalling pathways including ion channels protein serine/threonineand tyrosine phosphatases as well as phospholipases (PL) C and and the protein kinase C/mitogen activated protein kinase pathways.