Multiscale recursive medians, scale-space, and transforms with applications to image processing.

A cascade of increasing scale, 1-D, recursive median filters produces a sieve, termed an R-sieve, has a number of properties important to image processing. In particular, it (1) Simplifies signals without introducing new extrema or edges, that is, it preserves scale-space. It shares this property with Gaussian filters, but has the advantage of being significantly more robust. (2) The differences between successive stages of the sieve yield a transform, to the granularity domain. Patterns and shapes can be recognized in this domain using idempotent matched sieves and the result transformed back to the spatial domain. The R-sieve is very fast to compute and has a close relationship to 1-D alternating sequential filters with flat structuring elements. They are useful for machine vision applications.

Inhibition of electrical activity in mouse pancreatic beta-cells by the ATP/ADP translocase inhibitor, bongkrekic acid.

Bongkrekic acid causes fatal food poisoning which is associated with hyperglycaemia. Here we demonstrate that bongkrekic acid, a potent inhibitor of the mitochondrial ATP/ADP translocase, inhibits glucose-induced electrical activity in the pancreatic beta-cell through the stimulation of ATP-sensitive potassium channel (K-ATP-channel) activity. By comparison of its effects with those of oligomycin, we suggest that bongkrekic acid acts by the inhibition of glucose metabolism and may induce hyperglycaemia by impairing beta-cell function.

Pre-induction behaviour of children. A review of placebo-controlled trials of sedatives.

Placebo-controlled trials of sedative premedication in children are reviewed in an attempt to determine which drugs have been shown to reduce the frequency with which children cry or appear apprehensive. Small samples and inappropriate statistical methods limit the value of many of the studies. Most of the drugs tested will, in sufficient dose, increase the proportion of children who are asleep. Only intramuscular opioid analgesics, either alone or in combination with other drugs, have been shown repeatedly to increase the frequency of calm behaviour in those who are awake. There is some evidence, however, that intramuscular placebo controls have a lower frequency of calm behavior than oral placebo controls.

Data-sieving hydrophobicity plots.

Hydrophobicity plots provide clues to the tertiary structure of proteins (J. Kyte and R. F. Doolittle, 1982, J. Mol. Biol. 157, 105; C. Chothia, 1984, Annu. Rev. Biochem. 53, 537; T. P. Hopp and K. R. Woods, 1982, Proc. Natl. Acad. Sci. USA 78, 3824). To render domains more visible, the raw data are usually smoothed using a running mean of between 5 and 19 amino acids. This type of smoothing still incorporates two disadvantages. First, peculiar residues that do not share the properties of most of the amino acids in the domain may prevent its identification. Second, as a low-pass frequency filter the running mean smoothes sudden transitions from one domain, or phase, to another. Data-sieving is described here as an alternative method for identifying domains within amino acid sequences. The data-sieve is based on a running median and is characterized by a single parameter, the mesh size, which controls its resolution. It is a technique that could be applied to other series data and, in multidimensions, to images in the same way as a median filter.

Potassium and rubidium permeability and potassium conductance of the beta-cell membrane in mouse islets of Langerhans.

The efflux of 42K+ and 86Rb+ has been studied in collagenase-isolated normal mouse islets of Langerhans. In double-labelled experiments, the ratio of efflux rate constants of Rb+ and K+ (kRb/kK) was 0.80 in 5 mM-K+ and 0 glucose. The ratio was unaffected by glucose concentrations up to 22.2 mM. In the presence of 50 mM-K+, 0 glucose, the ratio increased to 0.91 and in 50 mM-Rb+, 0 glucose and 0 K+, the ratio was 1.06. With these limitations, the results indicate that 86Rb+ is an acceptable isotope for K+. Using the Goldman model, K+ and Rb+ permeability coefficients and K+ slope and chord conductances were computed. The permeabilities decreased in glucose and in high K+ or high Rb+. In the case of high external K+, the K+ conductances increased. Also there may be more than one type of K+ channel with differing selectivities to K+ and Rb+. The addition of glucose in the presence of 50 mM-K+ had no further effect on Rb+ permeability. It is suggested that there are about ten small K+ channels open in the resting beta-cell and that progressive closure of these channels is involved in the depolarization of the cell membrane that initiates spike activity.

Characterization of a cation channel on the apical surface of the frog lens epithelium.

The properties of a single conductance pathway of the apical (fibre-facing) surface of the frog lens epithelium are reported. Using the patch-clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981), the most common single-channel currents had an amplitude of 1.9 pA, the mean open time 2.1 ms and a conductance of 25 pS. One open-state time constant (to = 3.3 ms) and two closed-state time constants (tau c1 = 0.9 ms, tau c2 = 23.1 ms) were resolved. The channel current and the mean open time were both increased when Ca2+ was removed from the external solution and the open time distribution was no longer fitted by a single exponential. Multiple-channel events in cell-attached patches containing two or more identical channels were distributed in a binomial fashion and the probability that an individual channel was open, obtained by fitting the binomial distribution, was 0.039. The channel was found to have a Na+:K+ selectivity ratio of 3:1. When Ca2+ was removed from the pipette solution the probability that an individual channel was open increased to 0.137 and the Na+:K+ selectivity ratio increased to 4:1. Channel activity was observed in the presence of tetrodotoxin (10(-6) M) in the bathing medium and the pipette solution but was abolished by internal perfusion of the patch pipette with 0.5 x 10(-4) M amiloride. this apical conductance pathway is identified as an amiloride-sensitive cation channel. These channels are clustered in groups on the apical membrane, spontaneously active at the resting potential and with the possibility of altering their Na+:K+ selectivity. They represent a distinct type of channel, that differ from nerve and muscle Na+ channels in their manner of activation, but do share some common features with both Na+ and Ca2+ channels in excitable cells.

Microcomputers to control the pH of growing micro-organisms.

Negative feedback control can usefully be used in biochemistry for a variety of purposes. Two examples are presented which utilize microcomputers to generate the transfer function of the feedback loop. The first demonstrates the control of NADH concentration during an enzymic reaction, and the second shows that if the pH is held constant whilst growing E. coli the yield can be increased. In both these cases it is convenient, even essential, to use a computer because computers are both very stable over the long term and the feedback transfer function can be accurately and quickly specified.

Electrical coupling between cells in islets of Langerhans from mouse.

Two microelectrodes have been used to measure membrane potentials simultaneously in pairs of mouse pancreatic islet cells. In the presence of glucose at concentrations between 5.6 and 22.2 mM, injection of current i into cell 1 caused a membrane potential change in this cell, V1, and, provided the second microelectrode was less than 35 micron away, in a second impaled cell 2, V2. This result establishes that there is electrical coupling between islet cells and suggests that the space constant of the coupling ratio within the islet tissue is of the order of a few beta-cell diameters. The current-membrane potential curves i-V1 and i-V2 are very similar. By exchange of the roles of the microelectrodes, no evidence of rectification of the current through the intercellular pathways was found. Removal of glucose caused a rapid decrease in the coupling ratio V2/V1. In steady-state conditions, the coupling ratio increases with the concentration of glucose in the range from 0 up to 22 mM. Values of the equivalent resistance of the junctional and nonjunctional membranes have been estimated and found to change with the concentration of glucose. Externally applied mitochondrial blockers induced a moderate increase in the junctional resistance possibly mediated by an increase in intracellular Ca2+.

The interaction of detergents with bilayer lipid membranes.

Detergents are widely used for extracting and purifying membrane proteins. Four such detergents have been studied to find the extent to which they alone can alter black lipid film conductances. The slope of the plot of conductivity versus concentration for Triton X-100 is 4.54 in the range 0.025--0.15 mM; dodecyl sulphate 0.82 in the range 0.01--1 mM; sodium deoxycholate 1.03 in the range 0.01--1 mM and sodium cholate 1.37 in the range 0.1--10 mM. These ranges are below the respective critical micelle concentrations; above these concentrations the membranes break. Bilayer lipid membrane conductivity measured at constant detergent concentration increases with the conductivity of the bathing salt solution with a slope greater than 1, indicating an effect on the putative pore structures induced by detergents.

Titration of mitochondrial buffer by accumulated anions.

Acidimetric titration of intact rat liver mitochondria discloses a buffer power of about 45 mEquiv per g between pH 7 and 8, the value rises to 60 mEquiv per g per pH unit after lysis using Triton X-100. The existence and properties of this buffer system have been related to mitochondrial anion accumulation. The uptake of permeant anions by mitochondria occurs to a charge-dependent extent and they are in electrochemical equilibrium with each other and the protons as in a Donnan system. Adding permeant anion causes the intramitochondrial anion content to rise towards a saturation level, the inside to outside concentration ratio falls and concomitantly the transmembrane proton gradient diminishes, making the interior less alkaline. The falling internal pH is associated with protonation of the internal buffer, thus providing a second method for measuring the buffer power, a method which also tests the arguments used in the calculations. The titration curve is constructed by relating the internal pH (deduced from the permeant anion ratio) to the total internal anion equivalents which in turn determines the ionization state of the buffer because the sum of the internal anion equivalents, including the buffer anion, equals the equivalents of internal cation. The buffer power so measured agrees with the acidimetric method applied to lysed mitochondria. The disparity between the acidimetric data from lysed and unlysed mitochondria follows theoretical predictions.

The formation and properties of thin lipid membranes from HK and LK sheep red cell lipids.

Lipids were obtained from high potassium (HK) and low potassium (LK) sheep red cells by sequential extraction of the erythrocytes with isopropanol-chloroform, chloroform-methanol-0.1 M KCl, and chloroform. The extract contained cholesterol and phospholipid in a molar ratio of 0.8:1.0, and less than 1% protein contaminant. Stable thin lipid membranes separating two aqueous compartments were formed from an erythrocyte lipid-hydrocarbon solution, and had an electrical resistance of approximately 10(8) ohm-cm(2) and a capacitance of 0.38-0.4 microf/cm(2). From the capacitance values, membrane thickness was estimated to be 46-132 A, depending on the assumed value for the dielectric constant (2.0-4.5). Membrane voltage was recorded in the presence of ionic (NaCl and/or KCl) concentration gradients in the solutions bathing the membrane. The permeability of the membrane to Na(+), K(+), and Cl(-) (expressed as the transference number, T(ion)) was computed from the steady-state membrane voltage and the activity ratio of the ions in the compartments bathing the membrane. T(Na) and T(K) were approximately equal ( approximately 0.8) and considerably greater than T(Cl) ( approximately 0.2). The ionic transference numbers were independent of temperature, the hydrocarbon solvent, the osmolarity of the solutions bathing the membranes, and the cholesterol content of the membranes, over the range 21-38 degrees C. The high degree of membrane cation selectivity was tentatively attributed to the negatively charged phospholipids (phosphatidylethanolamine and phosphatidylserine) present in the lipid extract.