Receptors & channels最新文献

We have identified all currently sequenced members of the urea transporter (UT) family (TC #1.A.28). Homologues occur exclusively in vertebrate animals and bacteria but not in other eukaryotic kingdoms or archaea. Sequence, structural, and phylogenetic analyses reveal conserved regions and residues and suggest that a primordial 5 transmembrane helical segment (TMS)-encoding genetic element duplicated to give a 10 TMS-encoding element early during evolutionary history, at about the time when eukaryotes diverged from prokaryotes. Two well-conserved, strongly amphipathic, putative alpha-helices that precede both 5 TMS repeat elements are predicted to be of structural, functional, or biogenic significance. A second duplication event (or a gene fusion event) occurred during development of the vertebrate lineage, giving rise to 20 TMS mammalian homologues. The results suggest that vertebrates acquired UT genetic information from bacteria only once and that all current orthologues and paralogues in the animal kingdom arose from this one primordial system.

Muscarinic receptors expressed on smooth muscle cells are primarily of the M(2) and M(3) subtypes. The M(3) subtype triggers contraction through an interaction with G(q) proteins to stimulate phosphoinositide hydrolysis and mobilize Ca(2+). In contrast, activation of M(2) receptors modulates contraction by preventing relaxation or by potentiating M(3) receptor-mediated contractions, which enhances heterologous desensitization. These effects can be explained by the coupling of M(2) receptors to G(i) proteins that mediate an inhibition of adenylyl cyclase and calcium-activated potassium channels. The pharmacological antagonism of a response mediated through an interaction between M(2) and M(3) receptors has been shown to resemble the profile of the directly acting receptor (M(3)), primarily, and not that of the conditional receptor (M(2)). Evidence for a contractile role of the M(2) receptor has been obtained by inactivating its signaling pathway with pertussis toxin or by measuring contractile effects of muscarinic agonists after M(3) receptors have been covalently inactivated. Under these conditions, M(2) receptors have been shown to mediate an inhibition of the relaxant effects of agents, like isoproterenol, on the contractile effects of nonmuscarinic spasmogens. Muscarinic M(2) and M(3) receptor knockout mice are useful tools for exploring interactions between these receptors in smooth muscle.

Signal transduction mediated by heterotrimeric G proteins that couple to heptahelical receptors requires the involvement of many different proteins. Although some of the early evidence suggested that signal transduction components were assembled into complexes, much of the data supported an alternative hypothesis positing that the process involved transient interactions driven by random collision events. However, recent data indicate that many of the components involved in signal transduction do indeed form complexes. Here we review the evidence for these complexes and how they contribute to the specificity and efficiency of signaling in cells that must manage numerous signal transduction pathways.

The Cytosensor microphysiometer uses silicon chip technology to correlate changes in extracellular acidification rates with quantitative changes in cellular metabolism in response to ligand binding to surface receptors. This functional measure of physiology makes the Cytosensor a valuable tool in drug discovery research by allowing application of the instrument to screening of prospective pharmacologically active agents, characterizations of dose responses and structure-activity relationships, and investigation of mechanisms of action.

Biophysical properties of delayed rectifier K channels in the human neuroblastoma SH-SY5Y were established using patch clamp recordings. The whole cell K+ conductance activated at membrane potentials positive to -20 mV. The midpoint of current activation was 9.6 +/- 5.1 mV, the equivalent charge was 3.7 +/-.6. Whole-cell currents inactivated slightly with time constants of 700 ms and 5 s. The K+ currents were sensitive to micromolar concentrations of TEA and 4-aminopyridine. RT-PCR experiments amplified a cDNA fragment specific for human Kv3.1 channels. Activation gating parameters in outside-out patches were shifted by approximately 14 mV in the hyperpolarizing direction.

The human beta1-adrenoceptor (beta1AR) exists in several isoforms and activates adenylyl cyclase (AC) via Gs-proteins. The Arg389-isoform of the beta1AR (beta1AR-R389) expressed in CHW cells is much more efficient than the Gly389 isoform of the beta1AR (beta1AR-G389) at stabilizing the ternary complex and activating AC (Mason et al. 1999). The beta1AR-G389 fused to the Gsalpha splice variants GsalphaL or GsalphaS is efficient at stabilizing the ternary complex and activating AC (Wenzel-Seifert et al. 2002). Here, we show that beta1AR-R389-Gsalpha fusion proteins and beta1AR-G389-Gsalpha fusion proteins are similarly efficient at stabilizing the ternary complex and activating AC. In terms of agonist efficacies and agonist potencies in the [35S]guanosine 5'-O-(3-thiotriphosphate) binding assay, beta1AR-R389-Gsalpha fusion proteins and beta1AR-G389-Gsalpha fusion proteins are similar, too. Our present data fit to an increasing number of clinical studies that failed to detect physiology- or pathology-related functional differences between beta1AR-R389 and beta1AR-G389.