Drifts in real-time partial wavefront correction and how to avoid them.

In visual experiments that require real-time partial correction of wavefront aberrations, small errors occur that accumulate over time and lead to drifts in Zernike coefficients of the uncorrected aberrations. A simple algorithm that does not require the inclusion of an additional optical path to obtain independent measurements of the eye's aberrations is described here, and its effectiveness in preventing these drifts is demonstrated.

There is more to accommodation of the eye than simply minimizing retinal blur.

Eyes of children and young adults change their optical power to focus nearby objects at the retina. But does accommodation function by trial and error to minimize blur and maximize contrast as is generally accepted? Three experiments in monocular and monochromatic vision were performed under two conditions while aberrations were being corrected. In the first condition, feedback was available to the eye from both optical vergence and optical blur. In the second, feedback was only available from target blur. Accommodation was less precise for the second condition, suggesting that it is more than a trial-and-error function. Optical vergence itself seems to be an important cue for accommodation.

The challenge of improving boiling: lessons learned from a randomized controlled trial of water pasteurization and safe storage in Peru.

Boiling is the most common method of household water treatment in developing countries; however, it is not always effectively practised. We conducted a randomized controlled trial among 210 households to assess the effectiveness of water pasteurization and safe-storage interventions in reducing Escherichia coli contamination of household drinking water in a water-boiling population in rural Peru. Households were randomized to receive either a safe-storage container or a safe-storage container plus water pasteurization indicator or to a control group. During a 13-week follow-up period, households that received a safe-storage container and water pasteurization indicator did not have a significantly different prevalence of stored drinking-water contamination relative to the control group [prevalence ratio (PR) 1·18, 95% confidence interval (CI) 0·92-1·52]. Similarly, receipt of a safe-storage container alone had no effect on prevalence of contamination (PR 1·02, 95% CI 0·79-1·31). Although use of water pasteurization indicators and locally available storage containers did not increase the safety of household drinking water in this study, future research could illuminate factors that facilitate the effective use of these interventions to improve water quality and reduce the risk of waterborne disease in populations that boil drinking water.

Breast cancer screening: another point of view.

The breast cancer screening programmes (BCSP) are very controversial at the present time. They are evaluated by different socio-economic sectors, each with its own particular point of view. Large numbers of breast cancer cases are concentrated in the Oncology Services, which are, therefore, sensitive to the changes that these programmes could bring about. All patients attending the medical oncology and radiotherapy services of the Reina Sofia University Hospital, Cordoba from January 1994 until January 2003 were reviewed. Of 1785 patients, 829 went to these services after the start of the BCSP introduced in March 1999 and 956 before it. The variables analysed were age, presentation form, stage and treatment received. In conclusion, the BCSP has produced favourable changes with respect to stage (increasing the percentage of early breast cancer) and therapeutic management (increasing conservative surgery and decreasing the number of adjuvant treatments (radiotherapy and chemotherapy)). These changes are more outstanding in the population group covered by the BCSP.

Reciprocal regulation of expression of pore-forming KATP channel genes by hypoxia.

The ATP-sensitive potassium (KATP) channel is thought to play an important role in the protection of heart and brain against tissue hypoxia. The genetic regulation of the components of the channel by hypoxia has not been previously described. Here, we investigated the regulation of the two pore-forming channel proteins, Kir6.1 and Kir6.2, in response to hypoxia in vivo and in vitro. We find that these two structurally-related inwardly-rectifying potassium channel proteins are reciprocally regulated by hypoxia in vivo, with upregulation of Kir6.1 and down-regulation of Kir6.2, thereby resulting in a significant change in the composition of the channel complex in response to hypoxia. In vitro we describe neuronal and cardiac cell lines in which Kir6.1 is up-regulated by hypoxia, demonstrating that Kir6.1 is a hypoxia-inducible gene. We conclude that the heart and brain display genetic plasticity in response to hypoxic stress through specific genetic reprograming of cytoprotective channel genes.

Adenylate kinase phosphotransfer communicates cellular energetic signals to ATP-sensitive potassium channels.

Transduction of energetic signals into membrane electrical events governs vital cellular functions, ranging from hormone secretion and cytoprotection to appetite control and hair growth. Central to the regulation of such diverse cellular processes are the metabolism sensing ATP-sensitive K+ (K(ATP)) channels. However, the mechanism that communicates metabolic signals and integrates cellular energetics with K(ATP) channel-dependent membrane excitability remains elusive. Here, we identify that the response of K(ATP) channels to metabolic challenge is regulated by adenylate kinase phosphotransfer. Adenylate kinase associates with the K(ATP) channel complex, anchoring cellular phosphotransfer networks and facilitating delivery of mitochondrial signals to the membrane environment. Deletion of the adenylate kinase gene compromised nucleotide exchange at the channel site and impeded communication between mitochondria and K(ATP) channels, rendering cellular metabolic sensing defective. Assigning a signal processing role to adenylate kinase identifies a phosphorelay mechanism essential for efficient coupling of cellular energetics with K(ATP) channels and associated functions.

ATPase activity of the sulfonylurea receptor: a catalytic function for the KATP channel complex.

ATP-sensitive K+ (KATP) channels are unique metabolic sensors formed by association of Kir6.2, an inwardly rectifying K+ channel, and the sulfonylurea receptor SUR, an ATP binding cassette protein. We identified an ATPase activity in immunoprecipitates of cardiac KATP channels and in purified fusion proteins containing nucleotide binding domains NBD1 and NBD2 of the cardiac SUR2A isoform. NBD2 hydrolyzed ATP with a twofold higher rate compared to NBD1. The ATPase required Mg2+ and was insensitive to ouabain, oligomycin, thapsigargin, or levamisole. K1348A and D1469N mutations in NBD2 reduced ATPase activity and produced channels with increased sensitivity to ATP. KATP channel openers, which bind to SUR, promoted ATPase activity in purified sarcolemma. At higher concentrations, openers reduced ATPase activity, possibly through stabilization of MgADP at the channel site. K1348A and D1469N mutations attenuated the effect of openers on KATP channel activity. Opener-induced channel activation was also inhibited by the creatine kinase/creatine phosphate system that removes ADP from the channel complex. Thus, the KATP channel complex functions not only as a K+ conductance, but also as an enzyme regulating nucleotide-dependent channel gating through an intrinsic ATPase activity of the SUR subunit. Modulation of the channel ATPase activity and/or scavenging the product of the ATPase reaction provide novel means to regulate cellular functions associated with KATP channel opening.

Acquired resistance of a mammalian cell line to hypoxia-reoxygenation through cotransfection of Kir6.2 and SUR1 clones.

Reoxygenation after transient hypoxia is a common clinical condition that often causes greater tissue damage than persistent hypoxia itself. This warrants the development of a means to protect cells against hypoxia-reoxygenation injury. Adenosine triphosphate (ATP)-sensitive K+ (KATP) channels have been proposed to play an essential role in the mechanisms of endogenous cellular protection. Thus far, however, KATP channel proteins have not been exploited to generate an injury-resistant cellular phenotype by delivering KATP channel genes into injury-prone cells. A first step in this direction is the evaluation of the outcome of transferring genes encoding KATP channels into a KATP channel-deficient cell type exposed to metabolic stress. Untransfected COS-7 monkey kidney cells, which natively lack KATP channels, were found to be vulnerable to hypoxia-reoxygenation injury, which induced cytosolic Ca2+ loading, as measured by digital epifluorescent imaging. COS-7 cells cotransfected with KATP channel genes, Kir6.2 and SUR1, gained resistance to hypoxia-reoxygenation. This acquired resistance was abolished by glyburide, the KATP channel antagonist. We have previously shown that Kir6.2 and SUR1 physically associate to form a functional KATP channel, not reconstituted by either of the subunits alone. Transfection with individual channel subunits, Kir6.2 or SUR1, failed to produce resistance to hypoxia-reoxygenation induced Ca2+ loading. This is a first demonstration that transfer of KATP channel subunits can generate an injury-resistant cellular phenotype. The findings from this study may, thus, provide a framework for future therapeutic strategies based on gene delivery of KATP channel subunits in cells and tissues vulnerable to hypoxia-reoxygenation insults.

Evidence for direct physical association between a K+ channel (Kir6.2) and an ATP-binding cassette protein (SUR1) which affects cellular distribution and kinetic behavior of an ATP-sensitive K+ channel.

Structurally unique among ion channels, ATP-sensitive K+ (KATP) channels are essential in coupling cellular metabolism with membrane excitability, and their activity can be reconstituted by coexpression of an inwardly rectifying K+ channel, Kir6.2, with an ATP-binding cassette protein, SUR1. To determine if constitutive channel subunits form a physical complex, we developed antibodies to specifically label and immunoprecipitate Kir6.2. From a mixture of Kir6.2 and SUR1 in vitro-translated proteins, and from COS cells transfected with both channel subunits, the Kir6.2-specific antibody coimmunoprecipitated 38- and 140-kDa proteins corresponding to Kir6.2 and SUR1, respectively. Since previous reports suggest that the carboxy-truncated Kir6.2 can form a channel independent of SUR, we deleted 114 nucleotides from the carboxy terminus of the Kir6.2 open reading frame (Kir6.2deltaC37). Kir6.2deltaC37 still coimmunoprecipitated with SUR1, suggesting that the distal carboxy terminus of Kir6.2 is unnecessary for subunit association. Confocal microscopic images of COS cells transfected with Kir6.2 or Kir6.2deltaC37 and labeled with fluorescent antibodies revealed unique honeycomb patterns unlike the diffuse immunostaining observed when cells were cotransfected with Kir6.2-SUR1 or Kir6.2deltaC37-SUR1. Membrane patches excised from COS cells cotransfected with Kir6.2-SUR1 or Kir6.2deltaC37-SUR1 exhibited single-channel activity characteristic of pancreatic KATP channels. Kir6.2deltaC37 alone formed functional channels with single-channel conductance and intraburst kinetic properties similar to those of Kir6.2-SUR1 or Kir6.2deltaC37-SUR1 but with reduced burst duration. This study provides direct evidence that an inwardly rectifying K+ channel and an ATP-binding cassette protein physically associate, which affects the cellular distribution and kinetic behavior of a KATP channel.