Changes In Electrical Potential Difference Research Articles

Diurnal Variations in Vegetation Activity affecting Shallow Groundwater Flow identified by Microthermal Measurements

Observations of summer microthermal temperature variations suggest, next to hydrological factors, a significant influence of plant activity on groundwater flow in fractured claystone materials. Variations in groundwater microtemperature were compared to variations in meteorological parameters and electrical potential of plants. With an increase in surface temperature, relative air humidity decreases and an increase in tree electrical potential, measured as the difference between the northern and the southern stem exposure (N–S), can be observed. This increase in electrical potential is concomitant with a change in groundwater temperature of approximately 2 mK. This relationship does not always occur. At high temperatures (+30°C) the decrease amounts to just 1 mK. This fact is related to the change in transpiration of plants, decreased or even suspended at high surface temperatures. A frequency analysis of all data showed a daily frequency of high magnitude in all parameters. Possibly changes in the macro weather situation events were observed in the results of atmospheric pressure, southern electric potential and groundwater temperature. The lag time between changes in electric potential and subsurface microtemperature changes amounts to 17 hours, possibly a result of the electrical potential difference between the northern and the southern exposure of the stem (N–S), and 5 hours, the result of the change in electrical potential difference between the southern and the northern stem exposure side (S–N). A comparison between potential changes and the computed change in gravity resulting from earth tidal effects showed that the correlation between the subsurface temperature variation with up to 2 mK and the change in surface temperature variation does not match directly. Other study shows that the impact of earth tides on subsurface microtemperature variation amounts to ca. 1mK. The effect of groundwater abstraction by mature vegetation is determined at the same range. Atmospheric tides can be correlated with the changes in north and south electric potentials.

Comparison of fatigue life assessment by analytical, experimental and damage accumulation modelling approach for steel SAE 1045

AbstractFatigue life assessment for two‐phase steel SAE 1045 has been carried out by experimental and simulation techniques. Analytical approach, termed as fatigue lifetime calculation, was employed making use of a load increase testing procedure and constant amplitude tests equipped with measurement techniques – plastic strain amplitude, change in temperature and change in electrical potential difference. The predicted fatigue life has been validated by constant amplitude tests and compared with fatigue life estimation by microstructure‐based simulation. Simulation has been carried out over the complete cross section of the specimen. The simulation uses damage accumulation in the gage section of the specimen culminating in the macro‐crack propagation, taking into account the inhomogeneous fatigue resistance of the material element. The results show that at the initial intervals of high cycle fatigue range at relatively higher stress amplitudes, the experimental and simulation results are in agreement; whereas in the (high cycle fatigue) region at relatively low stress amplitudes, the simulation results were found more optimistic and the corresponding fatigue scatter is also increased. Each scatter is attributed to the relatively small number of analysed models of the material structure. Scanning electron microscope was used to determine volume fraction of the microstructure for simulation. Fatigue fracture surface analysis shows that crack initiated from internal defect of material and crack propagation is driven by silicon oxide inclusion.

Highlights From The Literature

Highlights From The Literature

A Micro-electrode Fast Data Capture Technique: Its Use to Examine Plant Cell Electrophysiology in the Wheat Root

Walker, C. D. and Graham, R. D. 1987. A micro-electrode fast data capture technique: its use to examine plant cell electrophysiology in the wheat root.—J. exp. Bot. 38: 355-366. Perturbations in the local electric field sensed during the passage of a micro-electrode through cellular tissue cannot be recorded with a conventional chart recorder because the response time is far too slow. This was overcome by using a micro-computer to record the rapid changes in electrical potential difference (PD). Transient PDs were rapidly collected and digitized, stored digitally, and replayed in analog at a slower speed afterwards. Some 'control' experiments to verify the speed of the data acquisition system and demonstrate the absence of quantitative artefacts in this procedure were performed. We have used this system to investigate cell PDs in the roots of wheat seedlings. Certain abrupt transients clearly represented the boundaries of the cells; this enabled further interpretation of individual cell PDs. Cyanide addition resulted in a major change in the transients within a minute, with a smaller component of the cell PD, interpreted as the diffusion potential, remaining. Ethanol treatment gave a predictable loss of membrane integrity, seen as discharging membrane PDs. The value of this new use of a digital data system is discussed.

Changes in electrical potential difference of rectal mucosa and of gallbladder bile constituents of dogs fed chenodeoxycholic acid.

Eighteen dogs were studied for 54 days. Rectal mucosal electrical potential difference (PD), gallbladder bile acids, cholesterol, and phospholipids were measured. It was shown that feeding chenodeoxycholic acid (CDCA) for 24 days in dosages of 15, 30, and 60 mg/kg of body weight, all depressed PD equally but significantly (P less than 0.05) in three groups of dogs compared with a control group. This depression was reversible 24 days after CDCA ingestion ceased in the two highest dosages. The low dose group was sacrificed after 24 days of CDCA feeding and the gallbladder bile was analyzed. CDCA and cholesterol were each significantly (P less than 0.05) elevated over control values in the gallbladder bile of these dogs. Phospholipids were not significantly changed. The PD, a reflection of Na+ -K+ ATPase activity, may be a useful indicator in maximizing dosages of CDCA in gallstone dissolution studies.

Changes in electrical potential difference and sodium-potassium ATPase of canine mucosa after jejunal-ileal bypass surgery.

Changes in electrical potential difference and sodium-potassium ATPase activity of rectal mucosa in dogs were examined before and after jejunal-ileal bypass surgery. The potential difference in the postoperative period was significantly higher (P less than 0.05) than the preoperative value. The potential difference increased by 160% at the 3rd day after the surgery, and then gradually declined with prolonged recovery periods. Ouabain-sensitive sodium-potassium ATPase activity also increased at the 3rd day (160%) and at the 10th day (86%) after the surgery. Fourteen days after the surgery the sodium-potassium ATPase activity returned almost to the preoperative value. These results indicated a close correlation between changes in transmucosal potential difference and sodium-potassium ATPase activity of rectal mucosa, suggesting a significant participation of sodium-potassium ATPase in changes of potential difference induced by jejunal-ileal bypass surgery.

COUPLING OF ION FLOWS IN CELL SUSPENSION SYSTEMS*

A valid test for cotransport between solutes is a demonstration that the degree of coupling between all coupled solute flows concerned, q defined in terms of Irreversible Thermodynamics, is sufficiently close to unity. The usual method to determine q kinetically by pulses and responses of flows can not simply be applied to rheogenic ion flows, as electrical potential difference changes due to the pulses can hardly be avoided. If, however, the ion flows are all electrically silent, changes in electrical potential difference (PD.) should not interfere with the determination of q. This holds for the furosemide-sensitive fluxes of Na+, K+, and Cl- in Ehrlich cells, each of which could be shown to be unaffected by a change in electrical PD and vice versa. Hence the q values could be determined for any pair of the three ion flows concerned and none differed significantly from unity. These results appear to indicate a furosemide-sensitive, electrically silent ternary symport mechanism for Na+, K+, Cl- with the stoichiometry 1:1:2, which is active but does not utilize ATP. It is assumed to function as a very efficient regulator of cellular volume and may be identical with other previously described binary symport systems.

Effects of changes in electrical potential difference on tubular potassium transport.

To assess directly the role of the transepithelial potential difference (PD) on potassium concentration differences across distal tubular epithelium, continuous and stationary microperfusion experiments were done in tubules voltage-clamped over a wide range of lumen-negative potentials. Potassium was measured either chemically or in situ by potassium-sensitive microelectrodes. Distal cell PD measurements show that most of the potential drop induced by luminal current injection occurred across the luminal cell membrane. Experiments were done in rats either on a control or on a high potassium diet and after amiloride administration. Luminal potassium was highly sensitive to imposed electrical potential changes, attainment of a new steady-state intraluminal potassium concentration was rapid (less than 1 s), and higher luminal potassium concentrations were observed in animals in which potassium secretion had been stimulated. Similar slopes of tubular fluid-to-plasma potassium ratios versus transepithelial potential differences were observed in all experiments. All slopes intersected, at zero PD, at a luminal tubular fluid-to-plasma concentration ratio in excess of unity, indicating the presence of an active component of potassium secretion.

Intravenous indomethacin and aspirin reduce basal gastric mucosal blood flow in dogs.

The effect of two known inhibitors of prostaglandin synthesis, indomethacin and aspirin, on blood flow was studied in six Heidenhain pouch and three antral pouch dogs. The unstimulated gastric mucosa was bathed with 0.15 M HCl and clearance of [14C]-aminopyrine was used as an index of changes in mucosal blood flow. [14C]aminopyrine clearance was measured during three 15-min predrug periods and five 15 min-postdrug periods. Either indomethacin (10 mg . kg-1), aspirin (100 mg . kg-1), or 0.15 M NaCl were given intravenously as a bolus. Indomethacin reduced mucosal blood flow in the Heidenhain pouch 52% (P less than 0.05) and in the antral pouch 52% (P less than 0.05). Aspirin reduced Heidenhain pouch mucosal blood flow 31% (P less than 0.05). Indomethacin caused no significant change in electrical potential difference or in net flux of H+ or Na+ in Heidenhain pouches. Indomethacin (10 mg . kg-1 iv) produced no change in mean arterial pressure. We conclude that indomethacin and aspirin reduce unstimulated gastric mucosal blood flow, suggesting that endogenous prostaglandin may contribute to its maintenance.

Gastric Mucosal Lesions Produced by Intravenous Infusion of Aspirin in Cats

Aspirin was given by continuous intravenous infusion to 35 intact cats for 7 days in doses ranging from 25 to 200 mg kg-1 day-1. Gastric mucosal lesions occurred in 50 to 70% of the animals in the various dosage groups, including deep ulcers in 20%. All of the ulcers were in antral mucosa near its border with oxyntic mucosa. The incidence of lesions, including ulcers, showed no apparent relation to the dose of aspirin. With all but the highest dose, plasma salicylate levels were within or below what is regarded as the therapeutic range for man. Asprin, 100 mg kg-1 day-1, was given for 7 days to 4 cats with pouches containing all of the antral mucosa plus some oxyntic mucosa. One or more deep ulcers occurred in the antral mucosa of the pouches in each of these 4 cats. The electrical potential difference across the mucosa did not decrease, and net fluxes of hydrogen ions out of the pouch and of sodium ions into the pouch did not increase during the 7 days of aspirin administration despite the occurrence of ulcers in the pouches. It is concluded that intravenous aspirin, in doses giving plasma levels within or below the therapeutic range for man, causes gastric mucosal lesions including deep ulcers within 7 days in cats. These lesions occur without the changes in electrical potential difference and hydrogen and sodium fluxes that are regarded as characteristic of the "broken barrier."

Bile Salts: A Determinant of the Bile-Peritoneal Electrical Potential Difference in the Rat

The electrical potential difference (PD) between bile and peritoneal cavity of the rat was determined in order to obtain additional information concerning the mechanism of bile formation in this species. A significant negative PD (− 4.4 ± 0.6 mv) was measured in the basal state at a time when the rat was secreting normal amounts of bile salts. The intravenous administration of sodium dehydrocholate produced a significant increase in negative PD, bile salt concentration, bile salt output, and bile flow. When non-bile salt dependent canalicular secretion was studied by creating a biliary fistula, there was a marked fall in PD, bile salt concentration, and bile salt output, but only a modest decrease in bile flow. Although the genesis of the PD cannot be determined with certainty, these changes in electrical PD correlated best with changes in bile salt concentration; the PD fell toward zero when non-bile salt dependent canalicular secretion was predominant. If the measured PD reflects canalicular events, non-bile salt dependent canalicular secretion may be associated with zero PD in the rat.

Regulation of phosphorylation of a specific protein in toad-bladder membrane by antidiuretic hormone and cyclic AMP, and its possible relationship to membrane permeability changes.

Phosphorylation of a specific protein was decreased in intact toad bladders by exposure to either antidiuretic hormone or monobutyryl cyclic AMP. The decrease in phosphorylation caused by these agents preceded the change in electrical potential difference (an indicator of the rate of sodium ion transport) observed in response to the same compounds. The addition of cyclic AMP to homogenates of toad bladder led to a decrease in phosphorylation of the same, or a similar, protein. In subcellular fractionation studies, the effect of cyclic AMP on the phosphorylation of this protein was observed in those fractions rich in membrane fragments, but not in the nuclear or cell-sap fractions. These and other results are compatible with the possibility that the regulation by vasopressin and cyclic AMP of sodium and/or water transport in toad bladder may be mediated through regulation of the phosphorylation of this specific protein.

Direct measurement of uptake of sodium at the outer surface of the frog skin.

A combination of the methods described by Schultz et al. (6) and by Ussing and Zerahn (9) was used to measure directly the unidirectional uptake of sodium from the outside solution into the frog skin, under short-circuit conditions. The sodium uptake was determined at six sodium concentrations ranging from 3.4 to 114 mM. NaCl was replaced by choline chloride in the solutions bathing both sides of the skin. Sodium uptake is not a linear function of sodium concentration but appears to be composed of two components, a saturating one and one that varies linearly with concentration. The sodium uptake is inhibited by the addition of lithium to the outside solution. The effect appears to be primarily on the saturating component and has the characteristics of competitive inhibition. In addition, lithium uptake by the skin is inhibited by sodium. The effects of lithium cannot be ascribed to changes in electrical potential difference. Measurements with microelectrodes indicate that under short-circuit condition there is no change in the intracellular potential when lithium chloride is added to the outside solution.

The Ionic Relations of Artemia Salina (L.)

ABSTRACT The effects of different external media on the sodium and chloride efflux in Artemia salina, the brine shrimp, have been observed, using animals acclimatized to sea water. In sea water, both sodium and chloride fluxes across the epithelium are approximately 7,000 pmole cm. −2 sec. −1. Sodium efflux drops markedly in sodium-free media, and chloride efflux falls in chloride-free media; the two effects are independent, and are not due to changes in external osmolarity. The decreases in sodium efflux can be explained by changes in electrical potential difference and diffusional permeability; exchange diffusion of sodium does not occur. Approximately 70 % of the chloride efflux is due to exchange diffusion, and most of the remainder is due to active transport. It is shown that graphs of ion efflux against external concentration which can be fitted by a Michaelis-Menten equation do not constitute evidence for the presence of exchange diffusion; graphs of similar shape can be obtained if the flux is simply diffusional. The drinking rate, determined from the rate of uptake of 131I-polyvinylpyr-rolidone, is 36 pl. sec. −1, or 2 ·0% body weight hr. −1. The diffusional influx of water is 240 pl. sec. −1.