Effects of substrate and ambient gas on epitaxial growth indium oxide thin films

Indium oxide thin films were grown by pulsed electron beam deposition method at 500 °C on c-cut sapphire and (0 0 1) oriented LaAlO3 single crystal substrates in oxygen or argon gas. The effects of ambient gas and substrate symmetry on the growth of indium oxide thin films were studied. Stoichiometric In2O3 films are formed in oxygen, while oxygen deficient In2O2.5 films are grown in argon, with In metallic nanoclusters embedded in a In2O3 matrix (nanocomposite films). In both cases, epitaxial In2O3 films having the bixbyite phase were grown with various orientation relationships, depending upon the substrate symmetry and gas ambient (oxygen or argon). Domain matching epitaxy was used to describe the precise in-plane epitaxial film-substrate relationships. The differences in film texture were correlated to the differences in growth conditions, while the differences in the film properties were correlated to the film oxygen composition

An ATP-regulated, inwardly rectifying potassium channel from rat kidney (ROMK)

Potassium channels exhibit a wide functional diversity making them well suited for their broad roles in renal (and other) cells [1, 2]. Potassium channels can be classified into two broad groups based on their functional/biophysical properties: the delayed or outward rectifiers that are activated by depolarizing potentials and the inward rectifiers that include the classical (strongly) inwardly rectifying K+ channel and the more weakly inwardly rectifying ATP-sensitive potassium (KATP) channels [1, 3–7]. The inward rectifiers are characterized by a lack of significant gating by voltage and by their ability to conduct potassium more readily in the inward than outward direction. The classical (strong) and KATP-type of inward rectifiers have been identified in a variety of excitable and nonexcitable cells. The strong inward rectifiers appear to function in maintaining the resting membrane potential and in regulating excitability (such as in cardiac muscle cells). ATP-sensitive potassium channels, on the other hand, open and close in response to cellular metabolic events and may serve important roles in some cells during ischemia. Renal KATP channels, while sharing many of the properties and characteristics of KATP channels found in other tissues (such as pancreatic β-cell and cardiac muscle cells [3]), lack sensitivity to TEA, have a much lower sensitivity to sulfonylureas (such as glyburide, a high affinity inhibitor of KATP channels found in heart and β-cells), and require higher (that is, mM) concentrations of ATP to inhibit channel activity [1, 7].In the kidney, the apical (K+ secretory) KATP channel serves a number of important roles in renal electrolyte transport [1]. In the thick ascending limb of Henle (TAL; both medullary, MTAL, and cortical, CTAL, segments; Fig. 1), KATP channels are the dominant conductance in apical plasma membranes and provide a crucial K+ efflux pathway for potassium entering cells via the apical Na+:K+:2Cl- cotransporter [1]. This recycling of potassium ensures that an adequate supply of luminal potassium is provided for efficient function of the Na+:K+:2Cl- cotransporter [1]. In addition, this channel mediates the apical component of a transcellular (basolateral-to-apical) current flow that returns to the basolateral side via the paracellular pathway predominantly as a sodium current [8]. This provides for one-half of the net transepithelial movement of sodium [9]. Two types of inwardly rectifying and ATP-sensitive K+ channels have been identified on apical membranes of TAL segments by patch clamp [10, 11]. Wang and coworkers [10] found a 20 to 30 pS K+ channel in rabbit TAL that had a high open probability (Po), was inhibited by ATP (mM) and not sensitive to TEA (referred to as the “low conductance” channel). On the other hand, a different KATP channel was identified on apical membranes of rat TAL by Greger and coworkers [11–13]; this channel also had a high Po and was ATP-sensitive but had a higher unitary conductance of ∼70 pS, was highly sensitive to reductions in cytosolic side pH (50% reduction in Po by a 0.2 pH unit decrease), and exhibited sensitivity to quinine or quinidine, TEA and Ca2+ (referred to as the “intermediate conductance” channel). Recently, Wang found both the low (∼30 pS) and intermediate (∼72 pS) conductance KATP channels in the same patches of rat TAL apical membranes [14]. He also confirmed that the intermediate conductance KATP channel is sensitive to quinidine and acidic pH while the low conductance channel is insensitive to quinidine. In addition, the low, but not the intermediate, conductance channel is inhibited by high (∼250 µM) gliburide. These studies demonstrate that there are two distinct channel types in apical membranes of TAL and that these channels can be distinguished by single channel conductances and their sensitivities to channel inhibitors.A functionally similar, if not identical, low conductance, inwardly rectifying KATP channel has been identified in apical membranes of principal cells in the cortical collecting duct (CCD) where it mediates K+ secretion into urine (Fig. 1) [1, 7, 15, 16]. The KATP channel in rat principal cells is dually regulated by ATP: high MgATP concentrations reversibly block channel activity (K1/2 = 0.6 to 1.0 mM) while lower concentrations of MgATP are required to maintain channel activity [1, 7, 17, 18]. The mechanism for ATP-mediated block of the principal cell KATP channel is unclear at present but may represent direct binding of nucleotide to the channel itself with a resulting change in channel conformation to the closed state and/or to altering the activity of the channel by regulating the phosphorylation of the channel itself, or some other protein involved to modulating channel activity. The stimulatory effect of low ATP concentration, however, clearly relates to regulation of channel activity by phosphorylation-dephosphorylation processes [18]: (i) channel activity rapidly diminishes (run-down) on patch excision unless the cytosolic face is exposed to low concentrations of MgATP; (ii) generally the catalytic subunit of cAMP-dependent protein kinase, PKA, is also required for channel maintenance and PKA, and together with MgATP can restore channel activity after run-down; (iii) non-hydrolyzable ATP analogues cannot maintain or restore channel activity; (iv) in patches in which channel activity is maintained by MgATP alone, the PKA inhibitor (PKI) reversibly reduces channel activity, providing evidence for an important role for endogenous PKA; and (v) PKC reversibly inhibits channel activity and antagonizes the stimulatory effect of PKA, a process that is Ca2+-dependent [19]. In further studies Wang and Giebisch [17, 18] demonstrated that the ratio of ATP to ADP and cell pH are also important regulators of the small conductance KATP channel in the apical membranes of principal cells. KATP channel activity in rat principal cells is also inhibited by activation of protein kinase C [19] or calcium-calmodulin-dependent kinase II [20] or by arachidonic acid [21].Much less is known about the regulation of the apical KATP channels in the TAL than in the CCD; however, we previously suggested that AVP (presumably cyclic AMP-dependent activation of PKA and subsequent phosphorylation of the channel or an associated regulatory protein) activated the K+ conductance of the apical membrane in mouse MTAL [22, 23]. Reeves and coworkers have provided more direct evidence for this [24]. They showed that Ba2+-sensitive, voltage-dependent 86Rb+ influx in membrane vesicles from rabbit outer medulla was activated by cAMP-dependent protein kinase. Wang [14] has confirmed this effect of cAMP-PKA by showing activation of the low conductance KATP channel in cell attached patches by AVP or cAMP and in excised patches by the catalytic subunit of PKA.Finally, it should be noted that large conductance (maxi-K+), Ca2+-activated K+ channels have been identified in apical membranes of both TAL [25, 26] and CCD [1, 27–29]. These voltage-gated channels are normally quiescent but can be activated by µM cytosolic Ca2+, are inhibited by TEA (more sensitive to TEA than the intermediate conductance KATP channel), and are insensitive to ATP. Since K+(Rb+) secretion and the transepithelial voltage in the CCD are not blocked by luminal TEA [16, 28], it is generally thought that this apical maxi-K+ channel is not directly involved in K+ secretion by this nephron segment. The maxi-K+ channel may function, however, as a K+ efflux pathway during cell swelling [1, 7, 30]

Electronic Correlations in CoO2, the Parent Compound of Triangular Cobaltates

A 59Co NMR study of CoO2, the x=0 end member of AxCoO2 (A = Na, Li...) cobaltates, reveals a metallic ground state, though with clear signs of strong electron correlations: low-energy spin fluctuations develop at wave vectors q different from 0 and a crossover to a Fermi-liquid regime occurs below a characteristic temperature T*~7 K. Despite some uncertainty over the exact cobalt oxidation state n this material, the results show that electronic correlations are revealed as x is reduced below 0.3. The data are consistent with NaxCoO2 being close to the Mott transition in the x -> 0 limit.Comment: 4 pages, submitte

Repeatability of prolactin responses to sulpiride in mares and geldings and the effect of pergolide and cabergoline

Four experiments were conducted in an effort to develop a method, based on prolactin secretion, for assessing the efficacy and duration of activity of dopaminergic agonists for the treatment of pituitary pars intermedia dysfunction (PPID) in horses. In the first experiment, prolactin response to a low dose of the dopamine antagonist, sulpiride, was generally repeatable in estrogen-primed geldings in winter over 8 every-other-day challenges. It was concluded that estrogen-primed, sulpiride-challenged geldings in winter could serve as a model for the study of potential dopaminergic drugs for the treatment of PPID in horses. The second experiment was performed in the summer with mares, and again tested the repeatability of the prolactin responses over a 30-day period. The responses in mares were generally repeatable, and there was no effect due to stage of the estrous cycle. It was concluded that mares could serve as a model for the study of potential dopaminergic drugs as well as geldings, and stage of the estrous cycle did not have to be taken into account. In the third experiment, two formulations of the dopamine agonist, pergolide, were tested (oral administration versus injection) against a single formulation of cabergoline (injected) and control injections (vehicle) for their efficacy to reduce unstimulated plasma prolactin concentrations in geldings. Oral pergolide reduced prolactin concentrations for a few hours, whereas injected pergolide suppressed prolactin concentrations for 24 hours. Cabergoline suppressed prolactin concentrations for up to 5.5 days. It was concluded that the injectable formulations had potential for further study as possible treatments for PPID in horses. The last experiment tested the efficacy of daily pergolide injection versus a single injection of cabergoline, for suppressing the prolactin secretion induced by low dose sulpiride injections in mares. Daily injection of pergolide suppressed prolactin responses as long as the injections were given, plus another 2 days. The single cabergoline injection suppressed prolactin responses for a minimum of 10 days. Based on these results, cabergoline in slow-release vehicle seems to provide an excellent possibility for administering dopaminergic activity to horses with PPID. Whether these results are directly applicable to PPID horses needs to be determined

First results in terrain mapping for a roving planetary explorer

To perform planetary exploration without human supervision, a complete autonomous rover must be able to model its environment while exploring its surroundings. Researchers present a new algorithm to construct a geometric terrain representation from a single range image. The form of the representation is an elevation map that includes uncertainty, unknown areas, and local features. By virtue of working in spherical-polar space, the algorithm is independent of the desired map resolution and the orientation of the sensor, unlike other algorithms that work in Cartesian space. They also describe new methods to evaluate regions of the constructed elevation maps to support legged locomotion over rough terrain