Impedance analysis of a tight epithelium using a distributed resistance model

SUMMARY1. The electrical resistance of the perfused frog lens was measured using separate internal current passing and voltage measuring electrodes.2. The resistance values obtained using voltage clamp and direct and alternating current techniques were in good agreement. 3. The voltage transients induced in response to current steps were multiexponential in form. Increasing the external K concentration reduced both the amplitude of the voltage response and the rise time.4. The impedance characteristics were investigated in more detail using alternating current analysis techniques.5. In an equivalent-circuit modelling study it was assumed that there were two major pathways for current flow in the lens. The first through the surface membranes and the second through the inner fibre membranes via the narrow extracellular spaces.6. The experimental impedance loci could not be adequately fitted by a simple two time constant model and a third time constant was introduced which may represent diffusion polarization effects in the extracellular spaces.7. The three time constant model gave good and consistent fits to impedance data from a number of preparations.8. The form of the impedance loci was also dependent on the external K concentration, but the only fitted parameter which changed consistently with external K was the surface membrane resistance (R8).

Section: Resultsmentioning

confidence: 99%

Impedance of the amphibian lens.

Duncan¹,

Patmore²,

Pynsent³

1981

“…Higher selectivity values will reduce the error between I.c and INa* It is interesting to note that Clausen, Lewis & Diamond (1979) using impedance analysis generated a relationship between apical conductance (Ga) and I, The slope of this curve will equal the net electrochemical driving force for this channel or pathway. The slope is 72 mV.…”

Section: Apical Selectivitymentioning

confidence: 99%

Apical membrane permeability and kinetic properties of the sodium pump in rabbit urinary bladder.

Lewis¹,

Wills²

1983

SUMMARY1. Previous studies have shown that aldosterone stimulates the rate of Na+ transport across the rabbit urinary bladder epithelium by increasing the apical membrane permeability to Na+. Paradoxically, ion-sensitive and conventional micro-electrode measurements demonstrated that intracellular Na+ activity aNa+ was essentially unchanged by aldosterone, i.e. aka+ was constant regardless of the rate of Na+ transport. The present study was designed to resolve this apparent contradiction.2. The effects of elevated, endogenous aldosterone levels produced by low-Na+ diet (Lewis & Diamond, 1976) on urinary bladder Na+ transport were investigated in vitro using Ussing-type chambers and intracellular conventional and ion-sensitive microelectrodes. Apical membrane selectivity and the kinetics of the Na+ pump were assessed as a function of hormone stimulation.3. The aldosterone-stimulated increase in Na+ transport was accounted for by increases in both the relative selective permeability of the apical membrane to Na+ and an increase in its absolute Na+ permeability.4. The kinetics of the Na+ pump were evaluated electrically by loading the cells with Na+ (monitored with Na+-sensitive micro-electrodes) or alternatively by manipulating serosal solution K+ concentration and measuring changes in the basolateral membrane electromotive forces and resistance. From these measurements the current generated by the pump was calculated as a function of intracellular Na+ or extracellular K+. The kinetics of the pump were not altered by aldosterone. A model of highly co-operative binding estimated Km for Na+ as 14-2 mm and 2-3 mm for K+. Hill coefficients for these ions were 2-8 and 1-8, respectively, consistent with a pump stoichiometry of 3 Na+ to 2 K+. The kinetic properties of the Na-K pump indicate that physiological levels of aka+ are poised at the foot of a step kinetic curve which energetically favours Na+ extrusion.

“…However, as generally found in biological tissues, the impedance locus consists of a semicircle with a 'depressed' centre, which 578 POTASSIUM CHANNEL BLOCKADE was attributed to distributed time constants (Clausen et al 1979). The equivalent impedance can be described by the following expression (Cole & Cole, 1941):…”

Section: Impedance Measurementsmentioning

confidence: 96%

“…Under conditions prior to the nystatin treatment, the electrical characteristics of the urinary bladder can be approximately described by the electrical impedance of a first-order system of which the electrical equivalent model consists of a simple parallel RC network with a series resistance (Clausen, Lewis & Diamond, 1979;Gogelein & Van Driessche, 1981). However, as generally found in biological tissues, the impedance locus consists of a semicircle with a 'depressed' centre, which 578 POTASSIUM CHANNEL BLOCKADE was attributed to distributed time constants (Clausen et al 1979).…”

Section: Impedance Measurementsmentioning

confidence: 99%

“…This analysis demonstrates that the apical membrane resistance was drastically reduced by nystatin and that secondly, the basolateral conductance increased. A more precise analysis ofthe impedance data can be done by using the distributed impedance model (Clausen et al 1979). However the use of this model requires additional information including the voltage divider ratio obtained from micro-electrode studies.…”

Section: Impedance Measurementsmentioning

confidence: 99%

See 1 more Smart Citation

Lidocaine blockage of basolateral potassium channels in the amphibian urinary bladder.

Driessche¹

1986

SUMMARY1. Basolateral membranes of the frog urinary bladder were investigated after increasing the cationic conductance of the apical membrane by the incorporation of nystatin.2. K+ currents were recorded in the presence of a mucosa to serosa oriented K+ gradient (SO42-Ringer solution). Nystatin caused a rapid rise of the short-circuit current (Ihe) followed by a slow increase over a period of 1-2 h.3. Impedance analysis showed that the apical membrane resistance was drastically reduced by nystatin. The slow increase in I., was accompanied by a progressive increase in basolateral conductance. 4. The transepithelial current and conductance recorded in the presence of nystatin could be depressed with lidocaine added to the mucosal and serosal solution. The effects of lidocaine were completely reversible.5. Noise analysis showed that lidocaine induced additional fluctuations in I,,.The spectrum of these fluctuations was of the Lorentzian type. This noise component is caused by the random interruption of the current through the basolateral K+ channels. The Lorentzian parameters were used to calculate the microscopic parameters of the basolateral K+ channels.