Ca modulates outward current throughI K1 channels

Summary Inward-rectifier channels in cardiac cells (I _K1) stabilize the resting membrane potential near the K equilibrium potential. Here we investigate the role ofI _K1 in the regulation of action potentials and link this to the influx of Ca during beating. Inward Ca current alters the open-channel probability of outwardI _K1 current. Thus Ca ions depolarize cells not only by carrying an inward current but also by blocking an outward current.     

Emerging functional roles for the glycosyl-phosphatidylinositol membrane protein anchor

Conclusion Experimental evidence has accumulated over the past few years to suggest that the GPI protein anchor may play a broad role in the regulation of membrane protein function. The significant changes in the biophysical properties of proteins that are membrane-anchored through GPI in lieu of a hydrophobic transmembrane peptide indicates a variety phobic transmembrane peptide indicates a variety of potential new functions served by the anchor structure itself. Moreover, the number of structural variations within the family of GPI molecules indicates a further opportunity for subspecialization of such anchored proteins, especially regarding cellular localization, mobility, metabolism and susceptibility to enzymatically-induced release. It is likely that further exploration of the structure and function of the GPI anchor may reveal additional roles for this unusual mechanism of membrane-protein attachment.     

Reconstituted voltage-sensitive sodium channels from eel electroplax: Activation of permeability by quaternary lidocaine,N-bromoacetamide,and N-bromosuccinimide

Summary We have investigated the ion permeability properties of sodium channels purified from eel electroplax and reconstituted into liposomes. Under the influence of a depolarizing diffusion potential, these channels appear capable of occasional spontaneous openings. Fluxes which result from these openings are sodium selective and blocked (from opposite sides of the membrane) by tetrodotoxin (TTX) and moderate concentrations of the lidocaine analogue QX-314. Low concentrations of QX-314 paradoxically enhance this channel-mediated flux. N-bromoacetamide (NBA) and N-bromosuccinimide (NBS), reagents which remove inactivation gating in physiological preparations, transiently stimulate the sodium permeability of inside-out facing channels to high levels. The rise and subsequent fall of permeability appear to result from consecutive covalent modifications of the protein. Titration of the protein with the more reactive NBS can be used to produce stable, chronically active forms of the protein. Low concentrations of QX-314 produce a net facilitation of channel activation by NBA, while higher concentrations produce block of conductance. This suggests that rates of modifications by NBA which lead to the activation of permeability are influenced by conformational changes induced by QX-314 binding.     

Genetic analysis of risk in clonal populations of forest trees

Summary A major concern arising from the culture of clonally propagated crops of forest trees is risk of catastrophic loss due to an agent or event not anticipated at the time of population establishment. Since danger of such a catastrophe depends to some degree on the genetic variability within clonal mixtures, attention has been focused on the number of clones needed to keep the risk of catastrophic loss below specified levels. In this paper, we describe a genetical analysis of susceptibility to a destructive agent and the effect that frequency of genes for susceptibility have on the number of clones needed to effectively manage this risk. As a part of the analysis, parameters representing the minimum unacceptable mortality rates in plantations () and acceptable levels of risk () are defined, and their effects on the number of single-pair matings needed for the production of clonal stock are evaluated. Dominance and recessive gene action models for a single two-allele genetic locus are investigated. Probabilities for plantation failure are functions of the gene frequency for the allele conferring susceptibility. These functions converge to zero for allele frequencies less than but to one for frequencies greater than or equal to . This convergence is periodic rather than monotonie, since probabilities for plantation failure increase rather than decrease over restricted ranges of increasing numbers of clones. Recessive and dominance gene actions are found to have different effects on the minimum number of clones needed to attain acceptable risk levels. For conditions in which substantial numbers of clones are required, selecting multiple clones per mating is an effective method for reducing the number of matings necessary to achieve acceptable risks.Paper No. 12480 of the Journal Series of the North Carolina Agriculture Research Service, Raleigh, NC 27695-7643, USA     

Characterisation of Human 5-Hydroxytryptamine2A and 5-Hydroxytryptamine2C Receptors Expressed in the Human Neuroblastoma Cell Line SH-SY5Y: Comparative Stimulation by Hallucinogenic Drugs

Abstract: Stable transfection of the human neuroblastoma cell line SH-SY5Y with the human 5-hydroxytryptamine_2A (5-HT_2A) or 5-HT_2C receptor cDNA produced cell lines demonstrating ligand affinities that correlated closely with those for the corresponding endogenous receptors in human frontal cortex and choroid plexus, respectively. Stimulation of the recombinant receptors by 5-HT induced phosphoinositide hydrolysis with higher potency but lower efficacy at the 5-HT_2C receptor (pEC₅₀ = 7.80 ± 0.06) compared with the 5-HT_2A receptor (pEC₅₀ = 7.30 ± 0.08). Activation of the 5-HT_2A receptor caused a transient fourfold increase in intracellular Ca²⁺ concentration. Whole-cell recordings of cells clamped at ?50 mV demonstrated a small inward current (2 pA) in response to 10 µM 5-HT for both receptors. There were no differences in potency or efficacy of phosphoinositide hydrolysis among four hallucinogenic [d-lysergic acid diethylamide (LSD), 1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI), 5-methoxy-N,N-dimethyltryptamine, and mescaline] and three nonhallucinogenic drugs (m-chlorophenylpiperazine, quipazine, and ergotamine). Comparison of equipotent doses producing 20% of the maximal response induced by 5-HT revealed selective activation of the 5-HT_2A receptor by LSD and to a lesser degree by DOI, mescaline, and ergotamine. Quipazine and 5-methoxy-N,N-dimethyltryptamine were relatively nonselective, whereas m-chlorophenylpiperazine selectively activated the 5-HT_2C receptor. It is unlikely therefore that hallucinosis is mediated primarily by activity at the 5-HT_2C receptor, whereas activity at the 5-HT_2A receptor may represent an important but not unique mechanism associated with hallucinogenic drug action.     

Inside or outside? Localization of the receptor relevant to auxin-induced growth

The localization of the auxin receptor relevant to the control of elongation growth is still a matter of controversy. Auxin-induced elongation of maize coleoptile segments was measured by means of a high resolution auxanometer. When indole-3-acetic acid (IAA) was removed from the bathing solution, a rapid cessation of auxin-induced elongation was detected. This decline was delayed when the auxin efflux carrier was blocked by the phytotropins naphthylphthalamic acid (NPA) and pyrenoylbenzoic acid (PBA) or by triiodobenzoic acid (TIBA). The IAA concentration in NPA-pretreated segments was 2–3 times higher than in NPA-free controls 35 min after the removal of IAA in the bathing medium.
A similar rapid drop of growth after removal of auxin was observed for the rapidly-transported synthetic auxin, naphthaleneacetic acid (NAA). When the auxin efflux was blocked, growth induced by NAA was sustained much longer than IAA-stimulated elongation.
In comparison with NAA, the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is known to be excreted very slowly by the efflux carrier. 2,4-D-induced growth remained at a stimulated level when the auxin was washed off, even in the absence of any auxin efflux inhibitor. We conclude from these results that the presence of intracellular auxin is a necessary and sufficient condition for sustained auxin-induced elongation growth, at least for the phases during the 2 h after its application. Consequently, we postulate the existence of an intracellular auxin receptor relevant to the control of growth.     

The Effect of Photoinhibition on Photosynthetic Oxygen Production in the Brown Alga Dictyota dichotoma

Photoinhibition of photosynthesis in the brown alga, Dictyota dichotoma, was studied with a PAM fluorometer (Walz, Effeltrich, Germany) and a homemade oxygen measuring device. As a measure of fluorescence, Fv/Fm, and for the photosynthetic yield, ΔF/Fm', were used. Oxygen measurements show clearly that the observed degree, as well as the time course, of photoinhibition depends on the fluence rate of the light used to measure changes of the production rate. After photoinhibition of photosynthesis the depression of oxygen production caused by non-saturating fluence rates was generally much more pronounced than that caused by saturating or nearly saturating fluence rates. At minimal photoinhibition the initial slope and the convexity of the fluence rate-response curve of oxygen evolution decrease, whereas the level of light saturation decreases only after strong photoinhibition. Nevertheless, at different degrees of photoinhibition, changes in the degree of the upper bending of the fluence rate-response curve of oxygen production are also linearly correlated to changes in the fluorescence ratios (Fv/Fm and ΔF/Fm'). The action spectrum of photoinhibition, calculated on the basis of changes of Fv/Fm, indicates that the reaction center of PS I is not involved in photoinhibition. The lower effectiveness of blue light in comparison to effects of green and red light may be due to chloroplast displacement, as in the so-called strong light position, the light absorbed by the thalli in vivo is decreased.     

Anti-inflammatory action of gentamycin through inhibitory effect on neutrophil NADPH oxidase activity

The effects of gentamycin on the NADPH oxidase (EC 1.6.99.6) from human neutrophils in both whole-cell and fully soluble (cell-free) systems were investigated. Gentamycin was found to inhibit, concentration-dependently, the superoxide generation of neutrophils exposed to phorbol myristate acetate in a whole-cell system and the activation of superoxide-generating NADPH oxidase by sodium dodecyl sulfate in a cell-free system. The concentrations of the drug required for 50% inhibition of the oxidase (IC₅₀) were 150 μM in the whole-cell system and 10 μM in the cell-free system. In addition, in the cell-free system, the drug did not change the K_m value for NADPH of the oxidase. However, gentamycin did not the superoxide generation of NADPH oxidase after its activation in the cell-free system, suggesting that the drug do not have superoxide-scavenger action. These results suggest that gentamycin, an aminoglycoside antibiotic, may exhibit an anti-inflammatory action due to inhibition of neutrophil NADPH oxidase activation.     

A novel, “hidden” penicillin-induced death of staphylococci at high drug concentration,occurring earlier than murosome-mediated killing processes

In log-phase cells of staphylococci, cultivated under high, non-lytic concentrations of penicillin G, there occurred a novel killing process hitherto hidden behind seemingly bacteriostatic effects. Two events are essential for the apprearance of this hidden death: (i) the failure of the dividing cell to deposit enough fibrillar cross-wall material to be welded together, and (ii) a premature ripping up of incomplete cross walls along their splitting system. Hidden death started as early as 10–15 min after drug addition, already during the first division cycle. It was the consequence of a loss of cytoplasmic constituents which erupted through peripheral slit-like openings in the incomplete cross walls. The loss resulted either in more or less empty cells or in cell shrinkage. These destructions could be prevented by raising the external osmotic pressure. In contrast, the conventional non-hidden death occurred only much later and exclusively during the second division cycle and mainly in those dividing cells, whose nascent cross walls of the first division plane had been welded together. These welding processes at nascent cross walls, resulting in tough connecting bridges between presumptive individual cells, were considered as a morphogenetic tool which protects the cells, so that they can resist the otherwise fatal penicillin-induced damages for at least an additional generation time (morphogenetic resistance system). Such welded cells, in the virtual absence of underlying cross-wall material, lost cytoplasm and were killed via ejection through pore-like wall openings or via explosions in the second division plane and after liberation of their murosomes, as it was the case in the presence of low, lytic concentrations of penicillin. Bacteriolysis did not cause any of the hitherto known penicillin-induced killing processes.Dedicated to Prof. Dr. Georg Henneberg on the occasion of his 85th birthday     

降钙素基因相关肽的研究进展

降钙素基因相关肽（ＣＧＲＰ）是由３７个氨基酸残基构成的生物活性多肽,与降钙素（ＣＴ）源子一个共同的基因。ＣＧＲＰ分布广泛,具有很强的血管扩张、降低血压以及心肌正性肌力作用等,并参与心血管系统稳态的调节。目前,ＣＧＲＰ已能人工合成,将为某些心血管疾病如高血压、心肌缺血、痉挛性或闭塞性周围血管疾病等的治疗提供一条崭新的途径。