Transepithelial potential difference

Drews, G. and K. Graszynski. 1987. The transepithelial potential difference in the gills of the fiddler crab, Uca tangeri influence of some inhibitors. Jour. Comp. Physiol. 157B 345-353. 

The ex vivo techniques of drug permeability using the Ussing chamber has extensively developed in the last few decades. It is very easy to monitor and therefore to maintain tissue viability throughout the study. This is ensured by monitoring the transepithelial potential difference and short-circuits current... 

Investigations of ion movements across epithelia have, however, only rarely been undertaken595 596 Using the mantle of the lamellibranches,4no(2onftf ranch s and Amblema costata, it has been shown that there was normally a transepithelial potential difference of 25 to 50 mV with the shell side positive. There was, however, no... 

Schafer JA, Troutman SL, Andreoli TE (1974) Volume reabsorption, transepithelial potential differences, and ionic permeability properties in mammalian superficial proximal straight tubules. J Gen Physiol 64 582-607 Schlatter E, Greger R, Weidtke C (1983) Effect of high ceiling diuretics on active salt transport in the cortical thick ascending limb of Henle s loop of rabbit kidney. Correlation of chemical structure and inhibitory potency. Pfltigers Arch 396 210-217... 

According to the CFF disease registry, 1.7% of CF patients had sweat chloride concentrations less than 60mmol/L (mean of 45.1mmol/L) and 0.5% had sweat chloride concentrations <40 mmol/L. These patients were diagnosed with CF on the basis of genotyping, nasal transepithelial potential difference studies, and clinical presentation. ... 

Fig. 1. Endogenous electric fields at epithelial wounds, (a) Schematic showing electric current flow (arrows) driven out the wound site by the transepithelial potential difference. (b) Small cut on human finger tip (/efl) and vibrating probe measuring current at the wound site (right), (c) Electrical currents at human finger wound, (b, c) are modified from (6).

At the other extreme, some amphibian epithelia, such as frog abdominal skin and toad urinary bladder, behave as tight epithelia. These are characterised by a high transepithelial potential difference and resistance, and very low hydraulic conductivity, and the shunt conductance is only a small fraction of the total conductance. 

Tamaoki J, Chiyotana A, Tagaya E, Takemura H, Konno K. Cholinergic control of rabbit transepithelial potential difference in vivo. Eur J Respir Dis 1966 8 1632-1636. 

Ion transport across membranes can be evaluated by using mucosal and serosal electrodes to read transepithelial current (I) and potential difference OP). With these parameters, equivalent circuit analysis can be utilized to account for the relative contributions of transcellular and paracellular pathways. Ionic flux (J) is defined by the Nernst-Planck equation,... 

Figure 4 Schematic representation of diffusion cell preparation for isolated tissue experiments. In this figure, PD represents the electrical potential difference (in millivolts) across the membrane and ISC, represents the current flow transepithelial resistance is PD. (From Ref. 62.)...

EFFECTS ON URINARY EXCRETION Since the late distal tubule and collecting duct have limited capacity to reabsorb solutes, blockade of Na+ channels in this part of the nephron only mildly increases the excretion rates of Na and Ck ( 2% of filtered load). Blockade of Na channels hyperpolarizes the luminal membrane, reducing the lumen-negative transepithelial voltage. Since the lumen-negative potential difference normally opposes cation reabsorption and facilitates cation secretion, attenuation of the lumen-negative voltage decreases the excretion rates of K+, H+, Ca +, and Mg +. Volume contraction may increase reabsorption of uric acid in the proximal tubule hence chronic administration of amiloride and triamterene may decrease uric acid excretion. Amiloride and triamterene have little or no effect on renal hemodynamics and do not alter TGF. 

Knowles MR, Carson JL, Collier AM, Gatzy JT, Boucher RC. Measurements of nasal transepithelial electric potential differences in normal human subjects in vivo. Am Rev Respir Dis 1981 124 484. 

SCHOFIELD There is some pH difference between the ambient water and the gill surface. At the present time, we don t have any means of measuring this. We haven t attempted it. There are some people in England looking at transepithelial potentials in relation to stresses from hydrogen ion which... 

The differences between the various types of epithelia do not seem to depend on the properties of the cell membranes themselves but rather on the variation in the properties of the tight junctions which join the epithelial cells together at their apical borders. When these tight junctions are not highly resistive, then the transepithelial potential is literally short-circuited through the tight junction. 

The mechanisms involved in urate reabsorption are not well known. The reabsorptive mechanism in at least a few species represents active transport urate may be reabsorbed from tubular fluid of the Cebus monkey when the concentration of urate is smaller than in the plasma and smaller than that predicted by the transepithelial electrical potential difference at equilibrium. Furthermore, in man and the chimpanzee, the concentration of urate in urine becomes smaller than that in the plasma when the secretion of urate is inhibited by the administration of pyrazinoic or pyrazinamide (Roch-Ramel and Weiner, 1980, review). 

Late Necturus Proximal Tubule Activity Ratios, Electrical Potential Differences, and Calculated Equilibrium Potentials Across the Tubular Epithelium (Transepithelial) and the Inner (Luminal) and Outer (Peritubular) Cell Boundaries. Mean Values Standard Error are Given. All Values Given are... 

By means of microelectrodes, it is possible to determine the potential profile of the intestinal epithdium. Also by this method it is possible to locate the site(s) at which the potential profile is changed under the influence of an added amino add or sugar. As shown in Table 3 the transepithelial potential (PD) is the algebraic sum of two potentials in series, the transserosal (PDs) and the transmucosal (PDm) potentials, opposite in sign and of different magnitixle. After addition of various amounts of L-alanine or D-glucose, the overall potential difference increases. This increase in potential difference is attributable solely to an increase in the transserosal potential... 

Mechanosensory bristle function in the adult fly can be used to assay the mechanotrans-duction machinery and characterize mutants defective in this mechanism or downstream function of the sensory neurons. Extracellular recordings of mechanically evoked bristle responses have been measured as a transepithelial potential (TEP), a voltage difference between the apical and basal sides of the sensory epithelium. The generation of the TEP serves as a general assay of mechanoreception. 

The first section of Table II represents the transepithelial parameters. The fluid/plasma K activity ratio of 1.9 0.2 is significantly greater than unity (P < 0.01) but is not significantly different from an inulin ratio of 1.5 0.2 in the latter part of the proximal tubule of the Necturus kidney. The potassium equilibrium potential (Ej ) calculated from the Nernst equation using the K" " activity ratio yield a value of 16.4 1.0 mV. This is not significantly different from the mean transepithelial PD of 14.5 A 1.5 mV. Thus K ion is in electro-chemical equilibrium distribution across the proximal tubular epithelium of Necturus. 

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