Receptors & channels最新文献

For most audiences, the term "diabetes" conjures thoughts of high levels of blood glucose and of the symptoms that characterize diabetes mellitus. In the last few years, a spirited campaign spear-headed by the families of affected individuals has made progress in educating nonprofessional and medical communities about diabetes insipidus (DI), the other disease characterized by polyuria (i.e., diabetes). Much work lies ahead to find better treatments for this affliction, but the progress in molecular biology over the last years made possible the identification of the genetic defects underlying the inherited forms of the disease. Numerous cases of adult-onset DI are triggered by toxic damage to the kidneys that impairs the concentrating capacity of the nephrons by a nonspecific mechanism. In these pages I shall deal mostly with the inherited forms of the disease. Diabetes insipidus is characterized by the inability of the kidneys of affected individuals to produce concentrated urine (Morello and Bichet 2001). The elimination of large volumes of diluted urine (polyuria) and excessive thirst (polydipsia) are the chief symptoms of the disease. Although this condition and the hints that it was a hereditary disease were described at the end of the 19th century, it took almost 100 years to gain molecular knowledge about its etiology. A brief review of the important role played by vasopressin in the maintenance of body fluids will help the reader understand the severity of this disease.

VIP and PACAP are two prominent neuropeptides that share two common G protein-coupled receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. This article reviews the present knowledge regarding various aspects of VPAC receptors including: 1) receptor specificity toward natural VIP-related peptides and pharmacology of synthetic agonists or antagonists; 2) genomic organization and chromosomal localization; 3) signaling and established or putative interactions with G proteins or accessory proteins such as RAMPs or PDZ-containing proteins; 4) molecular basis of ligand-receptor interaction as determined by site-directed mutagenesis, construction of receptor chimeras, and structural modeling; 5) constitutively active receptor mutants; 6) short-term (desensitization, internalization, phosphorylation) and long-term (transcription) regulations and transgenic models; 7) receptor polymorphisms.

Polymorphisms are quite common in the human population. Most likely every gene could be polymorphic. Most of these variations are common and have no functional consequence. However, as we learn more about the function of G-protein-coupled receptors (GPCRs) and how amino acid differences can modulate the function enough to measure, especially in a compromised physical state, the importance of characterizing these variations becomes substantial. This review will focus on polymorphisms in receptors that bind biogenic amines, calcium, opioids, endothelin, and those that also regulate taste, skin pigmentation, and oogenesis that have been suggested to cause variations of physiology.

Since 5-HT1B receptor mRNA was reported in rat aorta, and 5-HT1B receptor activation has been linked to vascular contraction, we explored sumatriptan-induced contractility and immunohistochemical density of 5-HT1B receptor protein in rat aorta. Sumatriptan (up to 10(-4) M), a 5-HT1B/1D receptor agonist, did not contract the endothelial intact or denuded rat aorta, even in the presence of L-NAME or after induction of modest tone with PGF2 alpha (10(-6) M). Sumatriptan also did not relax aortic preparations precontract with PGF2 alpha (3 x 10(-6) M) or phenylephrine (3 x 10(-7) M). Using a polyclonal antibody directed against the 5-HT1B receptor, minimal 5-HT1B receptor protein was detected in either the endothelium or smooth muscle of the rat aorta. However, dense 5-HT1B receptor protein was found in the vascular smooth muscle of the vasa vasorum supplying the aorta. Thus, the 5-HT1B receptor mRNA detected in tissue extracts of the rat aorta most likely reflects 5-HT1B receptor expression in the arterioles of the vasa vasorum. These studies support the link between the 5-HT1B receptor and vascular contraction in that the aorta with low density of 5-HT1B receptors lacked responses to sumatriptan, an agonist thought to contract blood vessels via 5-HT1B/1D receptors. Furthermore, caution must be observed when using 5-HT1B receptor mRNA to suggest receptor protein in tissues since this RT-PCR product may be derived predominantly from small blood vessels.