Protein secretion and the endoplasmic reticulum

In a complex multicellular organism, different cell types engage in specialist functions, and as a result, the secretory output of cells and tissues varies widely. Whereas some quiescent cell types secrete minor amounts of proteins, tissues like the pancreas, producing insulin and other hormones, and mature B cells, producing antibodies, place a great demand on their endoplasmic reticulum (ER). Our understanding of how protein secretion in general is controlled in the ER is now quite sophisticated. However, there remain gaps in our knowledge, particularly when applying insight gained from model systems to the more complex situations found in vivo. This article describes recent advances in our understanding of the ER and its role in preparing proteins for secretion, with an emphasis on glycoprotein quality control and pathways of disulfide bond formation.     

Population history and the selective landscape shape patterns of osmoregulatory trait divergence in tidal marsh Savannah sparrows (Passerculus sandwichensis)

A persistent challenge in making associations between phenotypic and environmental variation is understanding how ecological factors and demographic history interact to shape adaptive outcomes. Evaluating the degree to which conspecific populations exposed to similar environmental pressures respond in parallel provides a powerful framework for addressing this challenge. We took this comparative approach with multiple populations of Savannah sparrows (Passerculus sandwichensis) found in tidal marshes along the Pacific coast of North America. The high salinities characterizing tidal marshes select for increased osmoregulatory performance and salinity tolerance. We collected data on physiological traits associated with osmoregulatory performance from 10 tidal marsh and three freshwater-adapted interior populations to evaluate the degree of parallel divergence across populations. All traits showed differences in the magnitude of divergence, but only total evaporative water loss (TEWL) showed differences in the direction of divergence. The drivers of these differences in both the magnitude and direction of divergence varied among traits. For kidney morphology and TEWL, patterns of divergence were best explained by variation in immigration rate from interior populations. Maximum temperature was the best predictor of variation in urine excretion ability, and both gene flow and temperature contributed to variation in plasma osmolality. Finally, analysis of multitrait divergence patterns indicated that differences in the direction of divergence were best explained by population genetic structure, whereas differences in the magnitude of divergence were explained by environmental differences. Together these results show that the influences of demography and the selective landscape can manifest themselves differently across functionally integrated traits.     

Noncontact measurement of the local mechanical properties of living cells using pressure applied via a pipette

Mechanosensitivity in living biological tissue is a study area of increasing importance, but investigative tools are often inadequate. We have developed a noncontact nanoscale method to apply quantified positive and negative force at defined positions to the soft responsive surface of living cells. The method uses applied hydrostatic pressure (0.1-150 kPa) through a pipette, while the pipette-sample separation is kept constant above the cell surface using ion conductance based distance feedback. This prevents any surface contact, or contamination of the pipette, allowing repeated measurements. We show that we can probe the local mechanical properties of living cells using increasing pressure, and hence measure the nanomechanical properties of the cell membrane and the underlying cytoskeleton in a variety of cells (erythrocytes, epithelium, cardiomyocytes and neurons). Because the cell surface can first be imaged without pressure, it is possible to relate the mechanical properties to the local cell topography. This method is well suited to probe the nanomechanical properties and mechanosensitivity of living cells.     

Design and synthesis of S-(-)-2-[[4-(napht-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-a]pyrazine (CSP-2503) using computational simulation. A 5-HT1A receptor agonist

Based on a computational model for 5-HT(1A)R-ligand interaction and QSAR studies, we have designed and synthesized a new series of arylpiperazines 2-8 which exhibit high 5-HT(1A)R affinity and selectivity over alpha(1)-adrenergic receptors. Among them, compound CSP-2503 (4) has been pharmacologically characterized as a 5-HT(1A)R agonist at somatodendritic and postsynaptic sites, endowed with anxiolytic properties.     

TRPV channels as temperature sensors

The past year has seen a doubling in the number of heat-sensitive ion channels to six, and four of these channels are from the TRPV family. These channels characteristically have Q(10) values of >10 above the thermal threshold, very different from the Q(10) values of 1.5-2.0 seen in most ion channels. Cells expressing TRPV1 show similar temperature sensitivity to small capsaicin-sensitive nociceptor neurons, consistent with these neurons expressing homomers of TRPV1. A-delta fibres exhibit properties that may be explained by TRPV2 containing channels which is present in large diameter sensory neurons that do not express TRPV1. TRPV3 has a lower temperature threshold and may contribute to warm-sensitive channels together with TRPV1. Warm sensation may also be transduced by TRPV4 expressing sensory neurons and hypothalamic neurons. We can now look forward to further work defining the properties of the recombinant channels in more detail and a re-analysis of endogenous i(heat) currents in thermosensitive neurons and other cells. Data from the study of mice in which TRPV2, TRPV3 or TRPV4 have been deleted are also eagerly awaited.     

Synthesis and structure-activity relationships of a new model of arylpiperazines. Part 7: Study of the influence of lipophilic factors at the terminal amide fragment on 5-HT(1A) affinity/selectivity

The influence of lipophilic factors at the amide fragment of a new series of (+/-)-7a-alkyl-2-[4-(4-arylpiperazin-1-yl)butyl]-1,3-dioxoperhydropyrrolo[1,2-c]imidazoles 2 and of (+/-)-7a-alkyl-2-[(4-arylpiperazin-1-yl)methyl]-1,3-dioxoperhydropyrrolo[1,2-c]imidazoles 3 has been studied. Variations of logP have been carried out by introducing different hydrocarbonated substituents (R(1)) at the position 7a of the bicyclohydantoin, namely the non-pharmacophoric part. All the new compounds exhibit high potency for the 5-HT(1A) receptor; however, affinities for the alpha(1) receptor are high for compounds 2a-l while compounds 3a-f are selective over this adrenergic receptor. On the other hand, differences in logP do not notably affect the K(i) values for the above receptors.