Bidirectional control of airway responsiveness by endogenous cannabinoids

Smoking marijuana or administration of its main active constituent, delta9-tetrahydrocannabinol (delta9-THC), may exert potent dilating effects on human airways. But the physiological significance of this observation and its potential therapeutic value are obscured by the fact that some asthmatic patients respond to these compounds with a paradoxical bronchospasm. The mechanisms underlying these contrasting responses remain unresolved. Here we show that the endogenous cannabinoid anandamide exerts dual effects on bronchial responsiveness in rodents: it strongly inhibits bronchospasm and cough evoked by the chemical irritant, capsaicin, but causes bronchospasm when the constricting tone exerted by the vagus nerve is removed. Both effects are mediated through peripheral CB1 cannabinoid receptors found on axon terminals of airway nerves. Biochemical analyses indicate that anandamide is synthesized in lung tissue on calcium-ion stimulation, suggesting that locally generated anandamide participates in the intrinsic control of airway responsiveness. In support of this conclusion, the CB1 antagonist SR141716A enhances capsaicin-evoked bronchospasm and cough. Our results may account for the contrasting bronchial actions of cannabis-like drugs in humans, and provide a framework for the development of more selective cannabinoid-based agents for the treatment of respiratory pathologies.     

The mammalian sodium channel BNC1 is required for normal touch sensation

Of the vertebrate senses, touch is the least understood at the molecular level The ion channels that form the core of the mechanosensory complex and confer touch sensitivity remain unknown. However, the similarity of the brain sodium channel 1 (BNC1) to nematode proteins involved in mechanotransduction indicated that it might be a part of such a mechanosensor. Here we show that disrupting the mouse BNC1 gene markedly reduces the sensitivity of a specific component of mechanosensation: low-threshold rapidly adapting mechanoreceptors. In rodent hairy skin these mechanoreceptors are excited by hair movement. Consistent with this function, we found BNC1 in the lanceolate nerve endings that lie adjacent to and surround the hair follicle. Although BNC1 has been proposed to have a role in pH sensing, the acid-evoked current in cultured sensory neurons and the response of acid-stimulated nociceptors were normal in BNC1 null mice. These data identify the BNC1 channel as essential for the normal detection of light touch and indicate that BNC1 may be a central component of a mechanosensory complex.     

Urinary bladder hyporeflexia and reduced pain-related behaviour in P2X3-deficient mice

Extracellular ATP is implicated in numerous sensory processes ranging from the response to pain to the regulation of motility in visceral organs. The ATP receptor P2X3 is selectively expressed on small diameter sensory neurons, supporting this hypothesis. Here we show that mice deficient in P2X3 lose the rapidly desensitizing ATP-induced currents in dorsal root ganglion neurons. P2X3 deficiency also causes a reduction in the sustained ATP-induced currents in nodose ganglion neurons. P2X3-null mice have reduced pain-related behaviour in response to injection of ATP and formalin. Significantly, P2X3-null mice exhibit a marked urinary bladder hyporeflexia, characterized by decreased voiding frequency and increased bladder capacity, but normal bladder pressures. Immunohistochemical studies localize P2X3 to nerve fibres innervating the urinary bladder of wild-type mice, and show that loss of P2X3 does not alter sensory neuron innervation density. Thus, P2X3 is critical for peripheral pain responses and afferent pathways controlling urinary bladder volume reflexes. Antagonists to P2X3 may therefore have therapeutic potential in the treatment of disorders of urine storage and voiding such as overactive bladder.     

Messenger RNA targeting of rice seed storage proteins to specific ER subdomains

Rice seeds, a rich reserve of starch and protein, are a major food source in many countries. Unlike the seeds of other plants, which typically accumulate one major type of storage protein, rice seeds use two major classes, prolamines and globulin-like glutelins. Both storage proteins are synthesized on the endoplasmic reticulum (ER) and translocated to the ER lumen, but are then sorted into separate intracellular compartments. Prolamines are retained in the ER lumen as protein bodies whereas glutelins are transported and stored in protein storage vacuoles. Mechanisms responsible for the retention of prolamines within the ER lumen and their assembly into intracisternal inclusion granules are unknown, but the involvement of RNA localization has been suggested. Here we show that the storage protein RNAs are localized to distinct ER membranes and that prolamine RNAs are targeted to the prolamine protein bodies by a mechanism based on RNA signal(s), a process that also requires a translation initiation codon. Our results indicate that the ER may be composed of subdomains that specialize in the synthesis of proteins directed to different compartments of the plant endomembrane system.     

Direct imaging of the pores and cages of three-dimensional mesoporous materials

Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.     

Organoplatinum crystals for gas-triggered switches

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.     

Elevated UV-B radiation reduces genome stability in plants

Long-term depletion of the stratospheric ozone layer contributes to an increase in terrestrial solar ultraviolet-B radiation. This has deleterious effects on living organisms, such as DNA damage. When exposed to elevated ultraviolet-B radiation (UV-B; 280-315 nm), plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation. Here we show, using special sun simulators, that elevated solar UV-B doses increase the frequency of somatic homologous DNA rearrangements in Arabidopsis and tobacco plants. Increases in recombination are accompanied by a strong induction of photolyase and Rad51 gene expression. These genes are putatively involved in major DNA repair pathways, photoreactivation and recombination repair. In mutant Arabidopsis plants that are deficient in photoreactivating ultraviolet-induced cyclobutane pyrimidine dimers, recombination under elevated UV-B regimes greatly exceeds wild-type levels. Our results show that homologous recombination repair pathways might be involved in eliminating UV-B-induced DNA lesions in plants. Thus, increases in terrestrial solar UV-B radiation as forecasted for the early 21st century may affect genome stability in plants.