Cloning and function of the rat colonic epithelial K+ channel K(V)LQT1

K(V)LQT1 (K(V)LQ1) is a voltage-gated K+ channel essential for repolarization of the heart action potential that is defective in cardiac arrhythmia. The channel is inhibited by the chromanol 293B, a compound that blocks cAMP-dependent electrolyte secretion in rat and human colon, therefore suggesting expression of a similar type of K+ channel in the colonic epithelium. We now report cloning and expression of K(V)LQT1 from rat colon. Overlapping clones identified by cDNA-library screening were combined to a full length cDNA that shares high sequence homology to K(V)LQT1 cloned from other species. RT-PCR analysis of rat colonic musoca demonstrated expression of K(V)LQT1 in crypt cells and surface epithelium. Expression of rK(V)LQT1 in Xenopus oocytes induced a typical delayed activated K+ current. that was further activated by increase of intracellular cAMP but not Ca2+ and that was blocked by the chromanol 293B. The same compound blocked a basolateral cAMP-activated K+ conductance in the colonic mucosal epithelium and inhibited whole cell K+ currents in patch-clamp experiments on isolated colonic crypts. We conclude that K(V)QT1 is forming an important component of the basolateral cAMP-activated K+ conductance in the colonic epithelium and plays a crucial role in diseases like secretory diarrhea and cystic fibrosis.

Expression and function of colonic epithelial K(v)LQT1 K+ channels

1. K(V)LQT1 (KCNQ1) is a voltage-gated K+ channel essential for repolarization of the heart action potential Defects in ion channels have been demonstrated in cardiac arrhythmia. This channel is inhibited potently by the chromanol 293B, The same compound has been shown to block cAMP-dependent electrolyte secretion in rat and human colon, Therefore, it was suggested that a K+ channel similar to K(V)LQT1 is expressed in the colonic epithelium. 2, In the present paper, expression of K(V)LQT1 and its function in colonic epithelial cells is described. Reverse transcription-polymerase chain reaction analysis of rat colonic mucosa demonstrated expression of K(V)LQT1 in both crypt cells and surface epithelium. When expressed in Xenopus oocytes, K(V)LQT1 induced a typical delayed activated K+ current. 3, As demonstrated, the channel activity could be further activated by increases in intracellular cAMP. These and other data support the concept that K(V)LQT1 is forming a component of the basolateral cAMP-activated Kf conductance in the colonic epithelium.

The dorsomedial visual areas in New World and Old World monkeys: homology and function

The extrastriate cortex near the dorsal midline has been described as part of an 'express' pathway that provides visual input to the premotor cortex. This pathway is considered important for the integration of sensory information about the visual field periphery and the skeletomotor system, especially in relation to the control of arm movements. However, a better understanding of the functional contributions of different parts of this complex has been hampered by the lack of data on the extent and boundaries of its constituent visual areas. Recent studies in macaques have provided the first detailed view of the topographical organization of this region in Old World monkeys. Despite differences in nomenclature, a comparison of the visuotopic organization, myeloarchitecture and connections of the relevant visual areas with those previously studied in New World monkeys reveals a remarkable degree of similarity and helps to clarify the subdivision of function between different areas of the dorsomedial complex. A caudal visual area, named DM or V6, appears to be important for the detection of coherent patterns of movement across wide regions of the visual field, such as those induced during self-motion. A rostral area, named M or V6A, is more directly involved with visuomotor integration. This area receives projections both from DM/V6 and from a separate motion analysis channel, centred on the middle temporal visual area (or V5), which detects the movement of objects in extrapersonal space. These results support the suggestion, made earlier on the basis of more fragmentary evidence, that the areas rostral to the second visual area in dorsal cortex are homologous in all simian primates. Moreover, they emphasize the importance of determining the anatomical organization of the cortex as a prerequisite for elucidating the function of different cortical areas.

The microsomal epoxide hydrolase Tyr113His polymorphism: Association with risk of ovarian cancer

Functional significance has been demonstrated in vitro for the exon 3 T-->C Tyr113His amino acid substitution polymorphism of the microsomal epoxide hydrolase (EPHX) gene. The higher activity or fast TT genotype was previously reported to be associated with an increased risk of ovarian cancer, and this association may reflect enhanced activation of endogenous or exogenous substrates to more reactive and mutagenic derivatives. Components of cigarette smoke are examples of exogenous substrates subject to such bioactivation, and smoking exposure may thus modify the risk associated with the EPHX polymorphism. We examined 545 cases of epithelial ovarian cancer and 287 unaffected controls for this EPHXT-C genetic variant to investigate whether, in the Australian population, the TT genotype was associated with (i) specific ovarian tumor characteristics; (ii) risk of ovarian cancer, overall or for specific subgroups; and (iii) risk of ovarian cancer in smokers specifically. Genotyping was carried out using the Perkin-Elmer ABI Prism 7700 Sequence Detection System for fluorogenic polymerase chain reaction allelic discrimination. Stratification of the ovarian cancer cases according to tumor behavior (low malignant potential or invasive), grade, stage, and p53 immunohistochemical status failed to show any heterogeneity with respect to the genotype defined by the EPHX polymorphism. There was a suggestion of heterogeneity with respect to histologic subtype (P= 0.03), largely due to a decreased frequency of the TT genotype in endometrioid tumors. EPHX genotype distribution did not differ significantly between unaffected controls and ovarian cancer cases (overall, low malignant potential, or invasive) either overall or after stratification by smoking status. However, the TT genotype was associated with a decreased risk of invasive ovarian cancer of the endometrioid subtype specifically (age-adjusted odds ratio = 0.38, 95% confidence interval=0.17-0.87). The results suggest that the proposed EPHX-mediated bioactivation of components of cigarette smoke to mutagenic forms is unlikely to be involved in the etiology of ovarian cancer in general but that a greater rate of EPHX-mediated detoxification may decrease the risk of endometrioid ovarian cancer. (C) 2001 Wiley-Liss, Inc.

Polymorphisms at the glutathione S-transferase GSTM1, GSTT1 and GSTP1 loci: risk of ovarian cancer by histological subtype

The phase II glutathione S-transferases (GSTs) GSTT1, GSTM1 and GSTP1 catalyse glutathione-mediated reduction of exogenous and endogenous electrophiles. These GSTs have broad and overlapping substrate specificities and it has been hypothesized that allelic variants associated with less effective detoxification of potential carcinogens may confer an increased susceptibility to cancer. To assess the role of GST gene variants in ovarian cancer development, we screened 285 epithelial ovarian cancer cases and 299 unaffected controls for the GSTT1 deletion (null) variant, the GSTM1 deletion (null) variant and the GSTP1 codon 104 A-->G Ile-->Val amino acid substitution variant, The frequencies of the GSTT1, GSTM1 and GSTP1 polymorphic variants did not vary with tumour behaviour (low malignant potential or invasive) or p53 immunohistochemical status. There was a suggestion that ovarian cancers of the endometrioid or clear cell histological subtype had a higher frequency of the GSTT1 and GSTM1 deletion genotype than other histological subgroups. The GSTT1, GSTM1 and GSTP1 genotype distributions did not differ significantly between unaffected controls and ovarian cancer cases (overall or invasive cancers only). However, the GSTM1 null genotype was associated with increased risk of endometrioid/clear cell invasive cancer [age-adjusted OR (95% CI) = 2.04 (1.01-4.09), P = 0.05], suggesting that deletion of GSTM1 may increase the risk of ovarian cancer of these histological subtypes specifically. This marginally significant finding will require verification by independent studies.

No significant association between progesterone receptor exon 4 Val660Leu G/T polymorphism and risk of ovarian cancer

Epidemiological studies suggest that ovarian cancer is an endocrine-related tumour, and progesterone exposure specifically may decrease the risk of ovarian cancer. To assess whether the progesterone receptor (PR) exon 4 valine to leucine amino acid variant is associated with specific tumour characteristics or with overall risk of ovarian cancer, we examined 551 cases of epithelial ovarian cancer and 298 unaffected controls for the underlying G-->T nucleotide substitution polymorphism. Stratification of the ovarian cancer cases according to tumour behaviour (low malignant potential or invasive), histology, grade or stage failed to reveal any heterogeneity with respect to the genotype defined by the PR exon 4 polymorphism. Furthermore, the genotype distribution did not differ significantly between ovarian cancer cases and unaffected controls. Compared with the GG genotype, the age-adjusted odds ratio (95% confidence interval) for risk of ovarian cancer was 0.78 (0.57-1.08) for the GT genotype, and 1.39 (0.47-4.14) for the TT genotype. In conclusion, the PR exon 4 codon 660 leucine variant encoded by the T allele does not appear to be associated with ovarian tumour behaviour, histology, stage or grade. This variant is also not associated with an increased risk of ovarian cancer, and is unlikely to be associated with a large decrease in ovarian cancer risk, although we cannot rule out a moderate inverse association between the GT genotype and ovarian cancer.

Reduced expression of intercellular adhesion molecule-1 in ovarian adenocarcinomas

Ovarian adenocarcinomas develop as the result of multiple genetic, and epigenetic changes in the precursor ovarian surface epithelial (OSE) cells which result in a malignant phenotype. We investigated changes in gene expression in ovarian adenocarcinoma using a cDNA array containing 588 known human genes. We found that intercellular adhesion molecule-1 (ICAM-1) was expressed at lower levels in the ovarian tumour cell lines OAW42, PEO1 and JAM than in the immortalised human ovarian surface epithelial cell line HOSE 17.1. Further investigation revealed ICAM-1 was expressed in the surface epithelium of normal ovaries and both mRNA and protein expression levels were reduced in the majority of ovarian adenocarcinoma cell lines and primary tumours. ICAM-1 expression was increased in 8/8 cell lines treated with the de novo methyltransferase inhibitor 5-aza-2'-deoxycytidiine, indicating that methylation of CpG islands may play a role in the down-regulation of its expression in primary tumours. 'There was a significant association between patients whose tumours expressed ICAM-1 and survival (P = 0.03), suggesting that expression levels of ICAM-1 may have clinical relevance. (C) 2001 Cancer Research Campaign.

Derivation of the probability distribution function for the local density of states of a disordered quantum wire via the replica trick and supersymmetry

We consider the statistical properties of the local density of states of a one-dimensional Dirac equation in the presence of various types of disorder with Gaussian white-noise distribution. It is shown how either the replica trick or supersymmetry can be used to calculate exactly all the moments of the local density of states.' Careful attention is paid to how the results change if the local density of states is averaged over atomic length scales. For both the replica trick and supersymmetry the problem is reduced to finding the ground state of a zero-dimensional Hamiltonian which is written solely in terms of a pair of coupled spins which are elements of u(1, 1). This ground state is explicitly found for the particular case of the Dirac equation corresponding to an infinite metallic quantum wire with a single conduction channel. The calculated moments of the local density of states agree with those found previously by Al'tshuler and Prigodin [Sov. Phys. JETP 68 (1989) 198] using a technique based on recursion relations for Feynman diagrams. (C) 2001 Elsevier Science B.V. All rights reserved.

Noninvasive tests of vascular function and structure: Why and how to perform them

Background Early atherosclerosis involves the endothelium of many arteries. Information about peripheral arterial anatomy and function derived from vascular imaging studies such as brachial artery reactivity (BAR) and carotid intima media thickness (IMT) may be pertinent to the coronary circulation. The prevention and early treatment of atherosclerosis is gaining more attention, and these tests might be used as indications or perhaps guides to the effectiveness of therapy, but their application in clinical practice has been limited. This review seeks to define the anatomy and pathophysiology underlying these investigations, their methodology, the significance of their Findings, and the issues that must be resolved before their application. Methods The literature on BAR and IMT is extensively reviewed, especially in relation to clinical use. Results Abnormal flow-mediated dilation is present in atherosclerotic vessels, is associated with cardiovascular risk factors, and may be a marker of preclinical disease. Treatment of known atherosclerotic risk Factors has been shown to improve flow-mediated dilation, and some data suggest that vascular responsiveness is related to outcome. Carotid IMT is associated with cardiovascular risk factors, and increased levels can predict myocardial infarction and stroke. Aggressive risk factor management can decrease IMT. Conclusions BAR and IMT ate functional and structural markers of the atherosclerotic process. The clinical use of BAR has been limited by varying reproducibility and the influence by exogenous factors, but IMT exhibits less variability. A desirable next step in the development of BAR and IMT as useful clinical tools would be to show an association of improvement in response to treatment with improvement in prognosis.

Assessment of regional long-axis function during dobutamine echocardiography

Echocardiographic analysis of regional left ventricular function is based upon the assessment of radial motion. Long-axis motion is an important contributor to overall function. but has been difficult to evaluate clinically until the recent development of tissue Doppler techniques. We sought to compare the standard visual assessment of radial motion with quantitative tissue Doppler measurement of peak systolic velocity. timing and strain rate (SRI) in 104 patients with known or suspected coronary artery disease undergoing dobutamine stress echocardiography (DbE). A standard DbE protocol was used with colour tissue Doppler images acquired in digital cine-loop format. peak systolic velocity (PSV), time to peak velocity (TPV) and SRI were assessed off-line by an independent operator. Wall motion was assessed by an experienced reader. Mean PSV, TPV and SRI values were compared with wall motion and the presence of coronary artery disease by angiography. A further analysis included assessing the extent of jeopardized myocardium by comparing average values of PSV, TPV and SRI against the previously validated angiographic score. Segments identified as having normal and abnormal radial wall motion showed significant differences in mean PSV (7.9 +/- 3.8 and 5.9 +/- 3.3 cm/s respectively; P < 0.001), TPV (84 40 and 95 +/- 48 ms respectively; P = 0.005) and SRI (- 1.45 +/- 0.5 and - 1.1 +/- 0.9 s(-1) respectively; P < 0.001). The presence of a stenosed subtending coronary artery was also associated with significant differences from normally perfused segments for mean PSV (8.1 3.4 compared with 5.7 +/- 3.7 cm/s; P < 0.001), TPV (78 50 compared with 92 +/- 45 ms; P < 0.001) and SRI (- 1.35 0.5 compared with - 1.20 +/- 0.4 s(-1); P = 0.05). PSV, TPV and SRI also varied significantly according to the extent of jeopardized myocardium within a vascular territory. These results suggest that peak systolic velocity, timing of contraction and SRI reflect the underlying physiological characteristics of the regional myocardium during DbE, and may potentially allow objective analysis of wall motion.

A comparison of low-storage strategies for spectral analysis in dissipative systems: filter diagonalisation in the Lanczos representation and harmonic inversion of the Chebychev-order-domain autocorrelation function

We compare the performance of two different low-storage filter diagonalisation (LSFD) strategies in the calculation of complex resonance energies of the HO2, radical. The first is carried out within a complex-symmetric Lanczos subspace representation [H. Zhang, S.C. Smith, Phys. Chem. Chem. Phys. 3 (2001) 2281]. The second involves harmonic inversion of a real autocorrelation function obtained via a damped Chebychev recursion [V.A. Mandelshtam, H.S. Taylor, J. Chem. Phys. 107 (1997) 6756]. We find that while the Chebychev approach has the advantage of utilizing real algebra in the time-consuming process of generating the vector recursion, the Lanczos, method (using complex vectors) requires fewer iterations, especially for low-energy part of the spectrum. The overall efficiency in calculating resonances for these two methods is comparable for this challenging system. (C) 2001 Elsevier Science B.V. All rights reserved.

Genetics of brain function and cognition

There is overwhelming evidence for the existence of substantial genetic influences on individual differences in general and specific cognitive abilities, especially in adults. The actual localization and identification of genes underlying variation in cognitive abilities and intelligence has only just started, however. Successes are currently limited to neurological mutations with rather severe cognitive effects. The current approaches to trace genes responsible for variation in the normal ranges of cognitive ability consist of large scale linkage and association studies. These are hampered by the usual problems of low statistical power to detect quantitative trait loci (QTLs) of small effect. One strategy to boost the power of genomic searches is to employ endophenotypes of cognition derived from the booming field of cognitive neuroscience This special issue of Behavior Genetics reports on one of the first genome-wide association studies for general IQ. A second paper summarizes candidate genes for cognition, based on animal studies. A series of papers then introduces two additional levels of analysis in the ldquoblack boxrdquo between genes and cognitive ability: (1) behavioral measures of information-processing speed (inspection time, reaction time, rapid naming) and working memory capacity (performance on on single or dual tasks of verbal and spatio-visual working memory), and (2) electrophyiosological derived measures of brain function (e.g., event-related potentials). The obvious way to assess the reliability and validity of these endophenotypes and their usefulness in the search for cognitive ability genes is through the examination of their genetic architecture in twin family studies. Papers in this special issue show that much of the association between intelligence and speed-of-information processing/brain function is due to a common gene or set of genes, and thereby demonstrate the usefulness of considering these measures in gene-hunting studies for IQ.