Effects of prostaglandin E1, isoproterenol and forskolin on cyclic AMP levels and tension in rabbit aortic rings

The role of cyclic AMP in the control of vascular smooth muscle tone was studied by monitoring the effects of prostaglandin E1 (PGE1), isoproterenol and forskolin on cyclic AMP levels and tension in rabbit aortic rings. PGE1, isoproterenol and forskolin all increased cyclic AMP levels in rabbit aortic rings. Isoproterenol and forskolin relaxed phenylephrine-contracted aortic rings, but PGE1 contracted the rings in the presence or absence of phenylephrine. Isoproterenol relaxed these PGE1-contracted aortic rings without further change in total cyclic AMP levels, which were already elevated by the PGE1 alone. Pretreatment with forskolin potentiated the effects of PGE1 on cyclic AMP levels. PGE1 caused contractions in muscles partially relaxed by forskolin, even though very large increases in cyclic AMP levels (30 fold) were produced by PGE1 in the presence of forskolin. Isoproterenol was able to relax these forskolin-treated, PGE1-contracted muscles with no further increase in cyclic AMP levels. Thus, there does not appear to be a good correlation between total tissue levels of cyclic AMP and tension in these experiments. Our results suggest that, if cyclic AMP is responsible for relaxation of smooth muscle, some form of functional compartmentalization of cyclic AMP must exist in this tissue.     

Pre-synaptic dopaminergic compensation after moderate nigrostriatal damage in non-human primates

Despite a dramatic loss of nigrostriatal dopaminergic neurons in Parkinson's disease, clinical symptoms only arise with 70–80% reduction of striatal dopamine. The mechanisms responsible for this functional compensation are currently under debate. Although initial studies showed an enhanced pre-synaptic dopaminergic function with nigrostriatal degeneration, more recent work suggests that functional compensation is not dopamine-mediated. To address this issue, we used cyclic voltammetry to directly measure endogenous dopamine release from striatal slices of control monkeys and animals with a moderate or severe MPTP-induced dopaminergic lesion. The moderately lesioned monkeys were asymptomatic, while the severely lesioned animals were parkinsonian. In monkeys with a moderate lesion, a 300% increase was obtained in endogenous striatal dopamine release. In contrast, in striatal slices from severely lesioned animals, a small % of evoked dopamine signals were similar in amplitude to control while the greater majority were undetectable. These findings suggest that pre-synaptic dopaminergic compensation develops in residual dopaminergic terminals with moderate lesioning, but that this response is lost with severe nigrostriatal damage. Such an interpretation is supported by the results of dopamine turnover studies. This enhanced pre-synaptic dopaminergic activity may be important in maintaining normal motor function during the initial stages of Parkinson's disease.     

Phosphorylated guanine nucleotide exchange factor C3G,induced by pervanadate and Src family kinases localizes to the Golgi and subcortical actin cytoskeleton

Background  

The guanine nucleotide exchange factor C3G (RapGEF1) along with its effector proteins participates in signaling pathways that regulate eukaryotic cell proliferation, adhesion, apoptosis and embryonic development. It activates Rap1, Rap2 and R-Ras members of the Ras family of GTPases. C3G is activated upon phosphorylation at tyrosine 504 and therefore, determining the localization of phosphorylated C3G would provide an insight into its site of action in the cellular context.     

Analysis of among-site variation in substitution patterns

Substitution patterns among nucleotides are often assumed to be constant in phylogenetic analyses. Although variation in the average rate of substitution among sites is commonly accounted for, variation in the relative rates of specific types of substitution is not. Here, we review details of methodologies used for detecting and analyzing differences in substitution processes among predefined groups of sites. We describe how such analyses can be performed using existing phylogenetic tools, and discuss how new phylogenetic analysis tools we have recently developed can be used to provide more detailed and sensitive analyses, including study of the evolution of mutation and substitution processes. As an example we consider the mitochondrial genome, for which two types of transition deaminations (C⇒T and A⇒G) are strongly affected by single-strandedness during replication, resulting in a strand asymmetric mutation process. Since time spent single-stranded varies along the mitochondrial genome, their differential mutational response results in very different substitution patterns in different regions of the genome. Published: September 2, 2004.     

Isozyme polymorphism and virulence of Indian isolates of the rice sheath blight fungus

Inadequate information about the genetic structure of the polyphagous Rhizoctonia solani has made sheath blight resistance breeding a difficult task. To assess the variability in the Indian populations of sheath blight fungus, 18 isolates were collected from different rice growing regions of India and analyzed for virulence and electrophoretic profiles of 13 isozymes. The virulence spectrum of all 18 isolates was examined on susceptible IR50 and tolerant Swarnadhan varieties, based on which the isolates could be grouped as highly virulent, moderately virulent or a virulent. A total of 11 enzyme systems with 153 electrophoretic phenotypes were applied to characterize the genetic variation among the isolates. Cluster analyses based on isozyme patterns resulted in one major cluster comprising 16 virulent isolates, with two a virulent isolates loosely linked to this at 0.13 similarity. Isozyme systems of esterases (both and ) and 6-phosphogluconic dehydrogenase could be used to fingerprint the individual isolates.This revised version was published online in October 2005 with corrections to the Cover Date.     

Role of Nitrosomonas europaea NitABC iron transporter in the uptake of Fe3+-siderophore complexes

Nitrosomonas europaea has a single three-gene operon (nitABC) encoding an iron ABC transporter system (NitABC). Phylogenetic analysis clustered the subunit NitB with Fe³⁺-ABC transporter permease components from other organisms. The N. europaea strain deficient in nitB (nitB::kan) grew well in either Fe-replete or Fe-limited media and in Fe-limited medium containing the catecholate-type siderophore, enterobactin or the citrate-based dihydroxamate-type siderophore, aerobactin. However, the nitB::kan mutant strain was unable to grow in Fe-limited media containing either the hydroxamate-type siderophores, ferrioxamine and ferrichrome or the mixed-chelating type siderophore, pyoverdine. Exposure of N. europaea cells to a ferrichrome analog coupled to the fluorescent moiety naphthalic diimide (Fhu-NI) led to increase in fluorescence in the wild type but not in nitB::kan mutant cells. Spheroplasts prepared from N. europaea wild type exposed to Fhu-NI analog retained the fluorescence, while spheroplasts of the nitB::kan mutant were not fluorescent. NitABC transports intact Fe³⁺-ferrichrome complex into the cytoplasm and is an atypical ABC type iron transporter for Fe³⁺ bound to ferrioxamine, ferrichrome or pyoverdine siderophores into the cytoplasm. The mechanisms to transport iron in either the Fe³⁺ or Fe²⁺ forms or Fe³⁺ associated with enterobactin or aerobactin siderophores into the cell across the cytoplasmic membrane are as yet undetermined.