Responsiveness of a human parotid epithelial cell line (HSY) to autonomic stimulation: Muscarinic control of K+ transport

Summary Salivary electrolyte secretion is under the control of the autonomic nervous system. In this paper we report that HSY, an epithelial cell line derived from the acinar-intercalated duct region of the human parotid gland, responds to muscarinic-cholinergic (generation of Ca²⁺ signal) andβ-adrenergic (generation of cAMP signal), but not toα-adrenergic (lack of Ca²⁺ signal), receptor stimulation. The muscarinic response was studied in detail. Carbachol (10⁻⁴ M, muscarinic agonist) or A23187 (5 μM, calcium ionophore) stimulation of HSY cells increases both⁸⁶Rb (K⁺) influx and efflux, resulting in no change in net equilibrium⁸⁶Rb content. Atropine (10⁻⁵ M, muscarinic antagonist) blocks both the carbachol-generated Ca²⁺ signal and carbachol-stimulated⁸⁶Rb fluxes, but has no effect on either the A23187-generated Ca²⁺ signal or A23187-stimulated⁸⁶Rb fluxes. Carbachol- and A23187-stimulated⁸⁶Rb fluxes are substantially inhibited by two K⁺ channel blockers, quinine (0.3 mM) and scorpion venom containing charybdotoxin (33 μg/ml). The inhibition of these stimulated fluxes by another K⁺ channel blocker, tetraethylammonium chloride (5 mM), is less pronounced. Protein kinase C (PKC) seems to be involved in the regulation of the⁸⁶Rb fluxes as 10⁻⁷ M PMA (phorbol ester, phorbol-12-myristate-13-acetate) substantially inhibits the muscarinic-stimulated⁸⁶Rb efflux and influx. Because this concentration of PMA totally inhibits the carbachol-generated Ca²⁺ signal and only 80% of the muscarinic-stimulated⁸⁶Rb influx, it seems that a portion of the carbachol-stimulated⁸⁶Rb flux (i.e. that portion not inhibited by PMA) might occur independently of the Ca²⁺ signal. PMA fails to inhibit the A23187-stimulated⁸⁶Rb fluxes, however, suggesting that PKC regulates Ca²⁺-sensitive K⁺ channel activity by regulating the Ca²⁺ signal, and not steps distal to this event. 4-α-Phorbol-12,13-didecanoate, a phorbol ester which fails to activate PKC, fails to inhibit either the carbachol-stimulated increase in intracellular free Ca²⁺, or carbachol-stimulated⁸⁶Rb fluxes.     

Sensory rhodopsin I: Receptor activation and signal relay

Recent progress is summarized on the mechanism of phototransduction by sensory rhodopsin I (SR-I), a phototaxis receptor inHalobacterium halobium. Two aspects are emphasized: (i)The coupling of retinal isomerization to protein conformational changes. Retinal analogs have been used to probe chromophore-apoprotein interactions during the receptor activation process. One of the most important results is the finding of a steric trigger deriving from the interaction of residues on the protein with a methyl group near the isomerizing bond of the retinal (at carbon 13). Recent work on molecular genetic methods to further probe structure/function includes the synthesis and expression of an SR-I apoprotein gene designed for residue replacements by cassette mutagenesis, and transformation of anH. halobium mutant lacking all retinylidene proteins known in this species to SR-I⁺ and bacteriorhodopsin (BR)⁺. (ii)The relay of the SR-I signal to a post-receptor component. A carboxylmethylated protein (MPP-I) associated with SR-I and found in theH. halobium membrane exhibits homology with the signaling domain of eubacterial chemotaxis transducers (e.g.,Escherichia coli Tar, Tsr, and Trg proteins), suggesting a model based on SR-I MPP-I signal relay.     

Extracellular matrix and cell shape: potential control points for inhibition of angiogenesis.

Capillary endothelial (CE) cells require two extracellular signals in order to switch from quiescence to growth and back to differentiation during angiogenesis: soluble angiogenic factors and insoluble extracellular matrix (ECM) molecules. Soluble endothelial mitogens, such as basic fibroblast growth factor (FGF), act over large distances to trigger capillary growth, whereas ECM molecules act locally to modulate cell responsiveness to these soluble cues. Recent studies reveal that ECM molecules regulate CE cell growth and differentiation by modulating cell shape and by activating intracellular chemical signaling pathways inside the cell. Recognition of the importance of ECM and cell shape during capillary morphogenesis has led to the identification of a series of new angiogenesis inhibitors. Elucidation of the molecular mechanism of capillary regulation may result in development of even more potent angiogenesis modulators in the future.     

Hill coefficient-based stochastic switch-like signal directly governs damage-recovery dynamics in freshwater fish in response to pulse copper

Growing evidence demonstrates that fluctuating metal stressors can have profound impact on the ecophysiological responses in aquatic species. However, how environmental stochasticity affects the complex damage-recovery dynamics in organisms remains difficult to predict. The objective of this paper was to investigate the stochastic behavior in the damage-recovery dynamics in tilapia in response to pulse waterborne copper (Cu). We developed a mathematical framework that allows discrimination between damage and recovery processes in tilapia exposed to designed pulse Cu scenarios. We built deterministic nonlinear models for the damage-recovery dynamics that produce response surfaces describing killing/recovery rate–Cu-pulse interval interactions. Here we showed that the stochastic switching behavior arose from competition among killing, recovery rates, and Cu pulse frequency. This competition resulted in an ultrasensitivity appeared in whole body, gills, muscle, liver, and kidney with Hill coefficients of ≥7, 4, 7, 5, and 5, respectively, at Cu 3 mg L⁻¹, dilution rate 0.05 h⁻¹, and pulse interval 72 h, indicating that a stochastic switch-like response was generated. We argue that the role of gill-associated Hill coefficient as a direct signal of the stochastic switch-like response in the damage-recovery dynamics in response to pulse metal stressor can serve as a sensitive indicator for risk detection in fluctuating environments. Our approach constitutes a general method to identify the stochastic switch-like response for aquatic species exposed to fluctuating metal stressors, which may help to predict and, eventually, expand our understanding of the damage-recovery dynamics. Finally, we implicate that Hill coefficient-based switch-like signal and its damage with hazard response can be linked in an information theoretic framework to handle environmental stochasticity.     

转基因传播障碍中的文化因素辨析

近年来,转基因技术与产品在中国的传播遭遇了一定障碍.科学界和相关政府部门往往从科学知识的普及角度克服这些障碍.但实际上,转基因传播障碍的背后有着更为隐蔽的反智的社会态度及对传统农业的迷恋心理,三个因素都与中国传统直观外推思维方式有关.转基因传播所面临的实际是构造自然观与有机自然观之间的冲突.对有机自然观的误读与当前弥漫的反智主义关系密切,转基因带有“高科技”的突出特征,恰恰容易成为反智主义攻击的对象.在有机自然观和“反智”传统的影响下,社会上对传统农业的迷恋有着相当的市场.在此情况下,转基因技术要克服传播障碍,必须重构环境,除了以经济动力继续推动传播工作外,也要让技术发展与人们普遍接受的自然观相结合.     

Pronectin Promotes Calcium Signaling by Interferon-γ Human Neutrophils via G-Protein and Sphingosine Kinase-Dependent Mechanisms

A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-γ (IFN-γ) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-γ-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-γ responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-γ-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine I-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-γ partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-γ. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-γ induced calcium signals.     

Organismal Aging and Oxidants beyond Macromolecules Damage

The relationship between oxidants and organismal aging was first articulated through the free radical theory of aging. One of the major predictions of the free radical theory of aging is that oxidative stress shortens organisms’ lifespan because of an increased level of oxidants, which are damaging to macromolecules. However, challenging the role of oxidants in age‐related diseases, there is now sufficient evidence that antioxidant supplements do not provide significant health benefits. Interestingly, in addition to an increase in oxidant‐mediated macromolecules damage, there is convincing experimental data to support the role of senescent cells in the process of aging. Here, the current knowledge regarding the role of oxidants and cellular senescence in organismal aging is reviewed and it is proposed that, in addition to the role of oxidants as inducers of macromolecular damage, oxidants may also function as regulators of signaling pathways involved in the establishment of cellular senescence. If this role for oxidants is established, it may be necessary to modify the free radical theory of aging from “Organisms age because cells accumulate reactive oxygen species‐dependent damage over time” to: “Organisms age because cells accumulate oxidants’‐dependent damage and oxidants’‐dependent senescent characteristics over time.”