Overlapping LQT1 and LQT2 phenotype in a patient with long QT syndrome associated with loss-of-function variations in KCNQ1 and KCNH2

Long QT syndrome (LQTS) is an inherited disorder characterized by prolonged QT intervals and potentially life-threatening arrhythmias. Mutations in 12 different genes have been associated with LQTS. Here we describe a patient with LQTS who has a mutation in KCNQ1 as well as a polymorphism in KCNH2. The proband (MMRL0362), a 32-year-old female, exhibited multiple ventricular extrasystoles and one syncope. Her ECG (QT interval corrected for heart rate (QTc) = 518ms) showed an LQT2 morphology in leads V4-V6 and LQT1 morphology in leads V1-V2. Genomic DNA was isolated from lymphocytes. All exons and intron borders of 7 LQTS susceptibility genes were amplified and sequenced. Variations were detected predicting a novel missense mutation (V110I) in KCNQ1, as well as a common polymorphism in KCNH2 (K897T). We expressed wild-type (WT) or V110I Kv7.1 channels in CHO-K1 cells cotransfected with KCNE1 and performed patch-clamp analysis. In addition, WT or K897T Kv11.1 were also studied by patch clamp. Current-voltage (I-V) relations for V110I showed a significant reduction in both developing and tail current densities compared with WT at potentials >+20 mV (p < 0.05; n = 8 cells, each group), suggesting a reduction in IKs currents. K897T- Kv11.1 channels displayed a significantly reduced tail current density compared with WT-Kv11.1 at potentials >+10 mV. Interestingly, channel availability assessed using a triple-pulse protocol was slightly greater for K897T compared with WT (V0.5 = -53.1 ± 1.13 mV and -60.7 ± 1.15 mV for K897T and WT, respectively; p < 0.05). Comparison of the fully activated I-V revealed no difference in the rectification properties between WT and K897T channels. We report a patient with a loss-of-function mutation in KCNQ1 and a loss-of-function polymorphism in KCNH2. Our results suggest that a reduction of both IKr and IKs underlies the combined LQT1 and LQT2 phenotype observed in this patient.     

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.     

Protein flexibility and conformational state: a comparison of collective vibrational modes of wild-type and D96N bacteriorhodopsin

Far infrared (FIR) spectral measurements of wild-type (WT) and D96N mutant bacteriorhodopsin thin films have been carried out using terahertz time domain spectroscopy as a function of hydration, temperature, and conformational state. The results are compared to calculated spectra generated via normal mode analyses using CHARMM. We find that the FIR absorbance is slowly increasing with frequency and without strong narrow features over the range of 2-60 cm(-1) and up to a resolution of 0.17 cm(-1). The broad absorption shifts in frequency with decreasing temperature as expected with a strongly anharmonic potential and in agreement with neutron inelastic scattering results. Decreasing hydration shifts the absorption to higher frequencies, possibly resulting from decreased coupling mediated by the interior water molecules. Ground-state FIR absorbances have nearly identical frequency dependence, with the mutant having less optical density than the WT. In the M state, the FIR absorbance of the WT increases whereas there is no change for D96N. These results represent the first measurement of FIR absorbance change as a function of conformational state.     

Consolidation of dynamic motor learning is not disrupted by rTMS of primary motor cortex

Motor skills, once learned, are often retained over a long period of time. However, such learning first undergoes a period of consolidation after practice. During this time, the motor memory is susceptible to being disrupted by the performance of another motor-learning task. Recently, it was shown that repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex could disrupt the retention of a newly learned ballistic task in which subjects had to oppose their index finger and thumb as rapidly as possible. Here we investigate whether the motor cortex is similarly involved during the consolidation that follows learning novel dynamics. We applied rTMS to primary motor cortex shortly after subjects had either learned to compensate for a dynamic force field applied to their index finger or learned a ballistic finger abduction task. rTMS severely degraded the retention of the learning for the ballistic task but had no effect on retention of the dynamic force-field learning. This suggests that, unlike learning of simple ballistic skills, learning of dynamics may be stored in a more distributed manner, possibly outside the primary motor cortex.     

Transformation of Saccharopolyspora erythraea by electroporation of germinating spores: construction of propionyl Co-A carboxylase mutants

The introduction of plasmid DNA into germinating spores of an industrially improved strain of Saccharopolyspora erythraea was accomplished by electroporation. Various parameters affecting the efficiency of electroporation were examined. The most critical factor was the extent of spore germination. Electrocompetence was limited to a 4-h period following the initial emergence of the germ tube. Electroporation efficiencies as high as 2 × 10⁵ CFU μg⁻¹ of plasmid DNA were obtained using electrocompetent germlings. The optimal field strength was 12–14 kV cm⁻¹ with a pulse duration of 15–20 ms. Electrocompetent germlings were stored at −80°C without a significant decrease in transformation efficiency. The utility of this protocol was demonstrated by isolating a propionyl-CoA carboxylase mutant through targeted gene disruption and replacement. Received 3 April 1998/ Accepted in revised form 28 September 1998     

Identification of the 100-kD victorin binding protein from oats.

The fungus Cochliobolus victoriae, the causal agent of victoria blight of oats, produces the host-specific toxin victorin. Sensitivity of oats to victorin, and thus susceptibility to the fungus, is controlled by a single dominant gene. This gene is believed to also confer resistance to the crown rust pathogen Puccinia coronata. In the case of victoria blight, the gene has been hypothesized to condition susceptibility by encoding a toxin receptor. A 100-kD victorin binding protein (VBP) has been identified; it binds radiolabeled victorin derivatives in a ligand-specific manner and in a genotype-specific manner in vivo. The VBP may function as a toxin receptor. In vitro translation coupled with indirect immunoprecipitation was used to identify the mRNA for the 100-kD VBP, and fractionated mRNAs were used to prepare cDNA libraries enriched in the relative abundance of cDNA for the 100-kD VBP. A 3.4-kb cDNA clone was isolated that, when subjected to a 400-bp 5' deletion, was capable of directing the synthesis of a protein in Escherichia coli, which reacted to an antibody specific for the 100-kD VBP. Peptide mapping, by limited proteolysis, indicated that the protein directed by the cDNA is the 100-kD VBP. Nucleotide sequence analysis of the cDNA revealed extensive homology to a previously cloned cDNA for the P protein component of the multienzyme complex glycine decarboxylase. Glycine decarboxylase is a nuclear-encoded, mitochondrial enzyme complex. Protein gel blot analysis indicated that the 100-kD VBP copurifies with mitochondria. Based on analysis of in vitro translation products, nucleotide sequence homology, mitochondrial localization, and the widespread species distribution of the 100-kD VBP, we concluded that the 100-kD VBP is the P protein component of glycine decarboxylase.     

Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications

Evidence of associations between free-living amoebas and human disease has been increasing in recent years. Knowledge about phylogenetic relationships that may be important for the understanding of pathogenicity in the genera involved is very limited at present. Consequently, we have begun to study these relationships and report here on the phylogeny of Hartmannella vermiformis, a free-living amoeba that can harbor the etiologic agent of Legionnaires' disease. Our analysis is based on studies of small-subunit ribosomal RNA genes (srDNA). Nucleotide sequences were determined for nuclear srDNA from three strains of H. vermiformis isolated from the United Kingdom, Germany, and the United States. These sequences then were compared with a sequence previously obtained for a North American isolate by J. H. Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an average GC content of 49.6%. Sequence differences among the strains range are 0.38%-0.76%. Variation occurs at 19 positions and includes 2 single-base indels plus 14 monotypic and 3 ditypic single-base substitutions. Variation is limited to eight helix/loop structures according to a current model for srRNA secondary structure. Parsimony, distance, and bootstrap analyses used to examine phylogenetic relationships between the srDNA sequences of H. vermiformis and other eukaryotes indicated that Hartmannella sequences were most closely related to those of Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent with a separation between European and North American strains of Hartmannella, but results of other tests of this relationship were statistically inconclusive.      

Ouabain-insensitive salt and water movements in duck red cells. I. Kinetics of cation transport under hypertonic conditions

Duck red cells in hypertonic media experience rapid osmotic shrinkage followed by gradual reswelling back toward their original volume. This uptake of salt and water is self limiting and demands a specific ionic composition of the external solution. Although ouabain (10(-4)M) alters the pattern of cation accumulation from predominantly potassium to sodium, it does not affect the rate of the reaction, or the total amount of salt or water taken up. To study the response without the complications of active Na-K transport, ouabain was added to most incubations. All water accumulated by the cells can be accounted for by net salt uptake. Specific external cation requirements for reswelling include: sufficient sodium (more than 23 mM), and elevated potassium (more than 7 mM). In the absence of external potassium cells lose potassium without gaining sodium and continue to shrink instead of reswelling. Adding rubidium to the potassium- free solution promotes an even greater loss of cell potassium, yet causes swelling due to a net uptake of sodium and rubidium followed by chloride. The diuretic furosemide (10(-3)M) inhibits net sodium uptake which depends on potassium (or rubidium), as well as inhibits net sodium uptake which depends on sodium. As a result, cell volume is stabilized in the presence of this drug by inhibition of shrinkage, at low, and of swelling at high external potassium. The response has a high apparent energy of activation (15-20 kcal/mol). We propose that net salt and water movements in hypertonic solutions containing ouabain are mediated by direct coupling or cis-interaction, between sodium and potassium so that the uphill movement of one is driven by the downhill movement of the other in the same direction.