Indium-cadmium-oxide films having exceptional electrical conductivity and optical transparency: Clues for optimizing transparent conductors

Materials with high electrical conductivity and optical transparency are needed for future flat panel display, solar energy, and other opto-electronic technologies. InxCd1-xO films having a simple cubic microstructure have been grown on amorphous glass substrates by a straightforward chemical vapor deposition process. The x = 0.05 film conductivity of 17,000 S/cm, carrier mobility of 70 cm2/Vs, and visible region optical transparency window considerably exceed the corresponding parameters for commercial indium-tin oxide. Ab initio electronic structure calculations reveal small conduction electron effective masses, a dramatic shift of the CdO band gap with doping, and a conduction band hybridization gap caused by extensive Cd 5s + In 5s mixing.

Autocrine signaling through ATP release represents a novel mechanism for cell volume regulation.

Recovery of cell volume in response to osmotic stress is mediated in part by increases in the Cl- permeability of the plasma membrane. These studies evaluate the hypothesis that ATP release and autocrine stimulation of purinergic (P2) receptors couple increases in cell volume to opening of Cl- channels. In HTC rat hepatoma cells, swelling induced by hypotonic exposure increased membrane Cl- current density to 44.8 +/- 7.1 pA/pF at -80 mV. Both the rate of volume recovery and the increase in Cl- permeability were inhibited in the presence of the ATP hydrolase apyrase (3 units/ml) or by exposure to the P2 receptor blockers suramin and Reactive Blue 2 (10-100 microM). Cell swelling also stimulated release of ATP. Hypotonic exposure increased the concentration of ATP in the effluent of perfused cells by 170 +/- 36 nM in the presence of a nucleotidase inhibitor (P < 0.01). In whole-cell recordings with ATP as the charge carrier, cell swelling increased membrane current density approximately 30-fold to 16.5 +/- 10.4 pA/pF. These findings indicate that increases in cell volume lead to efflux of ATP through opening of a conductive pathway consistent with a channel, and that extracellular ATP is required for recovery from swelling. ATP may function as an autocrine factor that couples increases in cell volume to opening of Cl- channels through stimulation of P2 receptors.

Electrical currents associated with nucleotide transport by the reconstituted mitochondrial ADP/ATP carrier.

The electrophoretic export of ATP against the import of ADP in mitochondria bridges the intra- versus extramitochondrial ATP potential gap. Here we report that the electrical nature of the ADP/ATP exchange by the mitochondrial ADP/ATP carrier (AAC) can be directly studied by measuring the electrical currents via capacitive coupling of AAC-containing vesicles on a planar lipid membrane. The currents were induced by the rapid liberation of ATP or ADP with UV flash photolysis from caged nucleotides. Six different transport modes of the AAC were studied: heteroexchange with either ADP or ATP inside the vesicles, initiated by photolysis of caged ATP or ADP; homoexchange with ADPex/ADPin or ATPex/ATPin; and caged ADP or ATP with unloaded vesicles. The heteroexchange produced the largest currents with the longest duration in line with the electrical charge difference ATP4- versus ADP3-. Surprisingly, also in the homoexchange and with unloaded vesicles, small currents were measured with shorter duration. In all three modes with caged ATP, a negative charge moved into the vesicles and with caged ADP it moved out of the vesicles. All currents were completely inhibited by a mixture of the inhibitors of the AAC, carboxyatractyloside and hongkrekate, which proves that the currents are exclusively due to AAC function. The observed charge movements in the heteroexchange system agree with the prediction from transport studies in mitochondria and reconstituted vesicles. The unexpected charge movements in the homoexchange or unloaded systems are interpreted to reveal transmembrane rearrangements of charged sites in the AAC when occupied with ADP or ATP. The results also indicate that not only ATP4- but also ADP3- contribute, albeit in opposite direction, to the electrical nature of the ADP/ATP exchange, which is at variance with former conclusions from biochemical transport studies. These measurements open up new avenues of studying the electrical interactions of ADP and ATP with the AAC.