The gravitation-driven stress-reduced urothelial barrier in toad bladder urothelium

The urinary bladder urothelial are highly specialized epithelia that protect the underlying tissues from mechanical stress and seal them from the overlying fluid space. To better understand the maintaining permeability induced electrical potential roles played by urothelial in the bladder, we established a protocol of gravitation stress in toad urothelial, observed the transmembrane potential difference variation. Method: The toad urothelial were mounted in a using chamber which the chamber was separated to two solution spaces, and stable with 0.9% saline solution. The electrodes were settled on the surface of each side of the preparation, serosal side definite as cathode. The using chamber was settled in the centrifugal rotor and under 300 rpm rotation to obtain a vertically +4G gravitation on serosal chamber 5min. Result: a transient transmembrane potential difference increasing was observed after adding CaCl2 (3% solution) in serosal chamber. The amplitude increasing phase included a rapid and a slowly ascending phase. In gravitation stressed urothelial preparation, CaCl2 induced transient phase was significantly increased, furthermore the secondary slowly ascending phase was much more amplified on its amplitude axis and significantly prolonged on the time scale than that evoked in control preparations. The evoked total amplitude increasing were 10 times higher than that in control. Conclusion: The urinary bladder epithelial layer has a structure which regulates ion permeability as a barrier. The tight junction plays an important role as the intercellular coupling in the apical side of the epithelial cell. On the other hand, it is known that the ion channel exists on the epithelial cell membrane and regulates the physiological process. The gravitation stress weakened the tight junction. The transmembrane potential difference was enhanced both on its amplitude and prolonged time. The gravitation stress induced hyperpolarization that evoked by CaCl2 is one kind of Cl- transfer from serosal chamber in which high Ca2+ in the urothelial basal membrane activated the calcium-activated chloride channels. This outwardly rectifying chloride channel induced hyperpolarization can be blocked by Nppb.

Benzodiazepine Receptors in the Periphery

The benzodiazepines are almost universally thought to produce one and only one pharmacologic effect: positive allosteric modulation of GABAA receptors located in the brain. This results in an increased Cl−ion influx, greater negative transmembrane potential difference, and neurons that are less likely to fire in response to anxiety-producing stimulation. Unfortunately, the simplicity and success of this mono-target belief has distracted researchers and clinicians from studying and appreciating their other pharmacology. A glaring example is the general lack of awareness of the peripheral benzodiazepine receptor. The peripheral benzodiazepine receptor alters mitochondrial function (energy supply), cholesterol transport, and immune function. A patient who is on long-term benzodiazepine therapy (or withdrawing from them) will have these sites affected, just as are the sites located in the brain. One can easily imagine that the adverse effects associated with the peripheral sites would be fundamental, varied, and potentially profound—involving lack of energy, altered cholesterol metabolism, and aberrant immune function.

Analysis Of Antenna Radiation Of Broadband Pulses

Electromagnetic energy can alter metabolic and biosynthetic processes at certain pulse EMF parameters (pulse rate, opacity, power, exposure) can slow and suppress cell growth. Irradiation in the MM range of RNA and DNA containing the virus leads to a decrease in their infectivity. Inhibition of bacterial culture growth, alteration of phagocytic activity, protein biosynthesis, ultrastructural changes in cells with EHF EMF interaction. In studies with microorganisms, it was found that the biological effect of the effect of EMF on microorganisms was resonant. As one of the main mechanisms of the suppressive effect of EHF radiation on harmful microorganisms is the role of biological membranes in the response of microorganisms to EMF. Electrical phenomena occurring in biomembranes play an extremely important role. The formation of the transmembrane potential difference is due to the selective ionic conductivity of the membranes as a whole, it is an excellent dielectric, so that the biolayers of the insulating lipid molecules are able to withstand EP strengths of the order of 105 V / cm. The magnitude of the electrical potential on the membrane is extremely important. According to the modern theory of transmembrane transport, namely the EP inside the membrane, the fluxes of the necessary substances from the environment inside the cell and from the cell into the environment through special hydrophilic channels, most likely, are of a lipoprotein nature. The rate of ion penetration through the membrane is determined by such properties as thickness, value of DP, the presence of fixed electric charges on the membrane, the size and number of pores in the membrane, the presence of fixed charges in the pores and some others.

Temperature-dependent changes of membrane potentials in cells of thermonastic tepals of Eranthis hyemalis (L.) Salisb.

The effect of temperature upon the bioelectric potential across the plasma membrane in cells of tepals of <i>Eranthis hyemalis</i> (L.) Salisb. (Winter aconite) is described. Rapid warming of an intact tepal resulted in a transient small increase in the magnitude of transmembrane potential difference followed by a substantial long-lasting depolarization which is considered as an "anomalous" response. Upon rapid cooling the reverse response occurred: a small transient depolarization was followed by a substantial hyperpolarization (also an anomalous response). The anomalous responses were more pronounced in the epidermis on the abaxial side of the tepal than in that on the adaxial side, indicating an electrophysiological dorsiventrality of the tepals. The anomalous responses were much less apparent in cells of isolated tissues than in cells of intact tepals. This difference does not appear to result from wounding or bringing a tissue into direct contact with the external solution because in segments of tepals devoid of the abaxial epidermis only, the PD of the parenchyma behaved in a way similar to that of the intact tepals. It is suggested that the occurrence of the anomalous responses is modulated by the tissue stresses. The functional importance of the responses for thermonastic movements is discussed.

Effects of Chitosan onCandida albicans: Conditions for Its Antifungal Activity

The effects of low molecular weight (96.5 KDa) chitosan on the pathogenic yeastCandida albicanswere studied. Low concentrations of chitosan, around 2.5 to 10 μg·mL−1produced (a) an efflux of K+and stimulation of extracellular acidification, (b) an inhibition of Rb+uptake, (c) an increased transmembrane potential difference of the cells, and (d) an increased uptake of Ca2+. It is proposed that these effects are due to a decrease of the negative surface charge of the cells resulting from a strong binding of the polymer to the cells. At higher concentrations, besides the efflux of K+, it produced (a) a large efflux of phosphates and material absorbing at 260 nm, (b) a decreased uptake of Ca2+, (c) an inhibition of fermentation and respiration, and (d) the inhibition of growth. The effects depend on the medium used and the amount of cells, but in YPD high concentrations close to 1 mg·mL−1are required to produce the disruption of the cell membrane, the efflux of protein, and the growth inhibition. Besides the findings at low chitosan concentrations, this work provides an insight of the conditions required for chitosan to act as a fungistatic or antifungal and proposes a method for the permeabilization of yeast cells.

An update on renal peptide transporters

The brush-border membrane of renal epithelial cells contains PEPT1 and PEPT2 proteins that are rheogenic carriers for short-chain peptides. The carrier proteins display a distinct surface expression pattern along the proximal tubule, suggesting that initially di- and tripeptides, either filtered or released by surface-bound hydrolases from larger oligopeptides, are taken up by the low-affinity but high-capacity PEPT1 transporter and then by PEPT2, which possesses a higher affinity but lower transport capacity. Both carriers transport essentially all possible di- and tripeptides and numerous structurally related drugs. A unique feature of the mammalian peptide transporters is the capability of proton-dependent electrogenic cotransport of all substrates, regardless of their charge, that is achieved by variable coupling in proton movement along with the substrate down the transmembrane potential difference. This review focuses on the postcloning research efforts to understand the molecular physiology of peptide transport processes in renal tubules and summarizes available data on the underlying genes, protein structures, and transporter function as derived from studies in heterologous expression systems.

Ion fluxes considered in terms of membrane-surface electrical potentials

Ions transported through plasma membranes encounter electrical charges, and associated electrical potentials, at the membrane surfaces. The ionic composition of the tissue-bathing medium influences both the surface charge density and the surface electrical potential. Changes in surface electrical potential may affect ion transport by altering two components of the chemical potential difference (Δµj ) of an ion through the membrane. First, the surface activity of the transported ion will change because of electrostatic attraction or repulsion. Second, the surface-to-surface transmembrane potential difference will change. (This is different from the bulk-phase-to-bulk-phase transmembrane potential difference measured with microelectrodes.) These changes in the components of the chemical potential may change the flux of an ion through the membrane even if the surface-to-surface Δµj (equal to the bulk-phase-to-bulk-phase Δµj ) remains constant. The Goldman-Hodgkin-Katz (GHK) flux equation does not take into account these surface-potential effects. The equation has been modified to incorporate surface potentials computed by a Gouy-Chapman-Stern model and surface ion activities computed by Nernst equations. The modified equation (despite several additional deficiencies of the GHK model) successfully predicts many transport phenomena not predicted by the standard GHK equation. Thus electrostatic effects may account for saturation, cis- and trans-inhibition, rectification, voltage gating, shifts in voltage optima, and other phenomena also attributable to other mechanisms.

Symmetric pH dependence of buffering power in giant fused cells from frog kidney proximal tubule

This study measures the intrinsic buffering power (beta(i)) of giant fused cells from the proximal kidney tubule of the frog (Rana ridibunda) as a function of intracellular pH (pHi). We monitored pHi and transmembrane potential difference during acid or alkaline cell loading, achieved by removal of NH4Cl-containing solutions or CO2-HCO3(-)-equilibrated solutions, respectively, in the absence of extracellular Na+. Data were well fit by the equation for a single, monoprotic buffer with a maximum beta(i) at a pHi of 7.39 +/- 0.06 and a total buffer concentration of 30.7 +/- 1.6 mM (means +/- SD). From pHi measurements obtained during CO2-HCO3- exposure, we also calculated the buffering power afforded by the CO2-HCO3- pair, and we show its increasing contribution to total buffering power at increasing PCO2 and pHi. To our knowledge, this is the first report of a cell type in which intrinsic cell buffers can be adequately approximated as a single monoprotic buffer with a negative logarithm of apparent dissociation constant in the normal physiological range and essentially symmetric dependence on pHi in both acid and alkaline ranges.

Hepatic taurocholate uptake is electrogenic and influenced by transmembrane potential difference

Uptake of the bile acid taurocholate by hepatocytes is coupled to Na+ influx. The stoichiometry of uptake, however, is uncertain, as is the influence of the transmembrane electrical potential difference (PD) on this process. In this study, we examined the relationship between taurocholate extraction and PD (measured using intracellular microelectrodes) in perfused liver, and we measured taurocholate-induced transport current in cultured hepatocytes using patch-clamp recording techniques. In the perfused liver under basal conditions, PD averaged -28.4 +/- 0.6 (SE) mV, and extraction of 1, 50, and 300 microM taurocholate was 0.95 +/- 0.02, 0.98 +/- 0.01, and 0.41 +/- 0.03, respectively. When the Na+ chemical gradient was decreased by replacing perfusate Na+ with choline, the membrane depolarized to -17.2 +/- 1.1 mV, and taurocholate extraction markedly decreased at all taurocholate concentrations (P < 0.01). When perfusate Na+ concentration was held constant at 137 mM, membrane depolarization induced by substitution of gluconate for perfusate Cl- (-17.9 +/- 0.6 mV) or Cl- for nitrate (-10.3 +/- 2.1 mV) significantly decreased extraction of 300 microM taurocholate. Abrupt exposure to taurocholate produced a concentration-dependent membrane depolarization in the presence of Na+, but not in its absence (P < 0.001). In cultured hepatocytes, exposure to 100 microM taurocholate produced an inward current of -0.056 +/- 0.016 pA/pF at a holding potential of -40 mV. This current was Na+ dependent, and it increased twofold as holding potential was changed from -20 to -50 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroneutral uptake and electrogenic secretion of a fluorescent bile salt by rat hepatocyte couplets

The role of membrane voltage as a driving force for the hepatic uptake and secretion of fluorescent bile salts has been examined in isolated hepatocyte couplets. The present study demonstrates that the fluorescent bile salt derivative (N-[7-(nitrobenz-2-oxa- 1,3-diazol-4-yl)]-7-amino-3 alpha, 12 alpha-dihydroxy-5-cholan-24-oyl)-2-aminoethanesulfonate (7 beta-NBD-NCT) is taken up into hepatocytes by a saturable process with a Kt of 2.7 microM. Uptake rate was reduced by only 22% after total Na+ replacement and was independent of transmembrane potential difference over a range of -135 to +25 mV. In contrast, secretion into the canalicular space was strongly dependent on membrane voltage over the range from -34 to 0 mV in a manner consistent with electrodiffusion of an anion. Fitting the secretion time course to that predicted by electrodiffusion demonstrated that only approximately 50% of total secretion can result from electrodiffusion. Studies in isolated perfused liver confirmed this observation that depolarization caused a decrease in bile salt secretion rate. These results demonstrate that 7 beta-NBD-NCT is transported by a neutral uptake process at the sinusoidal membrane and is secreted across the canalicular membrane in part by electrogenic transport. This suggests that voltage changes could be a common pathway resulting in impaired organic anion secretion in diverse cholestatic syndromes.