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  • 1
    Electronic Resource
    Electronic Resource
    The effect of phenylalanine on the electrical properties of proximal tubule cells in the frog kidney (1985)
    Springer
    Pflügers Archiv 404 (1985), S. 138-144 
    Details
    ISSN: 1432-2013
    Keywords: Proximal tubule ; Cell membrane potential ; Potassium conductance ; Cell membrane resistance ; Sodium coupled transport ; Phenylalanine ; Frog kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study was designed to elucidate the effects of sodium-coupled transport on the electrical properties of proximal tubule cells in the isolated perfused frog kidney. Cable analysis techniques have been employed to determine the resistance of the luminal and peritubular cell membranes in parallel (R m) and the apparent ratio of the luminal over the peritubular cell membrane resistance (VDR). Furthermore, the sensitivity of the potential difference across the peritubular cell membrane (PDpt) to 6-fold increases of peritubular potassium concentration (ΔPDk) was taken as a measure of the relative potassium conductance of this membrane. In the absence of luminal phenylalanine, PDpt amounts to −60±1 mV (n=90),R m to 36±3 kΩ cm (n=22), VDR to 1.81±0.14 (n=20), and ΔPDk to 15.0±0.9 mV (n=25). The application of 10 mmol/l phenylalanine replacing 10 mmol/l raffinose leads to a rapid (within 30 s) depolarisation of PDpt to 50±5% of its control value and to a delayed (within 12 min) recovery to 95±5% of control. The rapid depolarisation is associated with a decline ofR m and VDR, indicating a decrease mainly of the luminal cell membrane resistance. During recovery of PDpt there is a parallel increase of VDR and a further decline ofR m pointing to a decline of the basolateral cell membrane resistance. ΔPDk is decreased during rapid depolarisation but increases again during the recovery phase. Thus, phenylalanine initially decreases but then increases above control the apparent potassium conductance. Removal of phenylalanine leads to a transient hyperpolarisation and increased apparent potassium conductance. If a cell is depolarised by current injection into a neighbouring cell, a similar decrease of ΔPDk is observed which shows also a similar recovery (partial repolarisation) despite continued injection of constant current. The data point to a potential-dependent peritubular K+-conductance (of the inwardly rectifying type) and to a regulatory increase within some ten minutes, when the cell is depolarised either by sodium entry across the luminal cell membrane or by current injection into a neighbouring cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585409
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of potassium depletion on potassium conductance in proximal tubules of frog kidney (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 153-157 
    Details
    ISSN: 1432-2013
    Keywords: Potassium depletion ; Intracellular potassium activity ; Cell membrane potential ; Cell membrane resistance ; Potassium conductance ; Proximal tubule ; Amphibian kidney ; Barium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to test for the contribution of intracellular potassium activity to the link of sodium/potassium-ATPase activity and potassium conductance, studies with conventional and potassium selective microelectrodes were performed on proximal tubules of the isolated perfused frog kidney. The peritubular transference number for potassium (t k), i.e., the contribution of peritubular slope potassium conductance to the slope conductance of the cell membranes (luminal and peritubular), was estimated from the influence of peritubular potassium concentration on the potential difference across the peritubular cell membrane (PD pt). During control conditions,PD pt is −65±1 mV, intracellular potassium activity (K i) 57±2 mmol/l andt k 0.41±0.05. The resistance in parallel of the luminal and peritubular cell membranes (R m) is 44±4 kΩcm, the resistance of the cellular cable (R c) 137±13 MΩ/cm. When the cells are exposed 10 min to potassium free perfusates (series I),PD pt increases by −28±3 mV within 2 min and then decreases gradually to approach the control value within 10 min.K i decreases by 22±3 mmol/l andR c increases by 35±10%. After a transient decrease,R m increases by 36±9%. Readdition of peritubular potassium leads to a transient increase ofPD pt, a gradual decrease ofR m andR c as well as a gradual increase ofK i t k recovers only slowly to approach 65±8% of control value within 3 and 79±10% within 6 min. When the cells are exposed 10 min to potassium free perfusates containing 1 mmol/l barium (series II),PD pt depolarizes by +28±4 mV andK i decreases by 7±1 mmol/l within 10 min. Within 2 min of reexposure to control perfusatesPD pt approaches the control value.t k recovers significantly faster than in series I and approaches 92±8% of control value within 3 min and 107±8% within 6 min reexposure to control perfusates. In conclusion, the effect of potassium free perfusates on peritubular potassium conductance depends on the degree of potassium depletion of the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580667
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  • 3
    Electronic Resource
    Electronic Resource
    Further characterization of volume regulatory decrease in cultured renal epitheloid (MDCK) cells (1991)
    Springer
    Pflügers Archiv 418 (1991), S. 35-39 
    Details
    ISSN: 1432-2013
    Keywords: MDCK Cells ; Cell membrane resistance ; Potassium conductance ; Anion conductance ; Cell volume regulation ; Intracellular pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In Madin Darby canine kidney (MDCK) cells volume regulatory decrease (VRD) is paralleled by a variable, transient hyperpolarization followed by a sustained depolarization of the cell membrane. In the depolarized cells, the cell membrane selectivity is decreased for potassium and increased for chloride. Without knowledge of the cell membrane resistance (R m), these changes of cell membrane selectivity cannot be translated into conductances, i.e. the observed alterations of ion selectivity could have been due to inhibition of potassium conductance or activation of anion conductance. In the present study R m has been determined by cellular cable analysis. To this end, three microelectrodes were impaled into three different cells of a cell cluster, current (up to 3 nA) was injected into one cell and the corresponding voltage deflections determined in the other two cells. As a result, exposure of the cells to hypotonic perfusates leads to a marked, sustained reduction of R m. In the absence of chloride and in the absence of bicarbonate and chloride, the decrease of R m is only transient. The data indicate that cell swelling leads to a transient increase of potassium conductance followed by a sustained increase of anion conductance. As evident from BCECF fluorescence, exposure of MDCK cells to hypotonic perfusates leads to a significant decrease of intracellular pH, which may in part be due to loss of bicarbonate through the anion conductive pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370449
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of cell membrane resistance in cultured renal epithelioid (MDCK) cells: effects of cadmium and mercury ions (1990)
    Springer
    Pflügers Archiv 417 (1990), S. 29-36 
    Details
    ISSN: 1432-2013
    Keywords: MDCK cells ; Potassium conductance ; Cell membrane potential ; Cell membrane resistance ; Barium ; Cadmium ; Mercury ; Gap junctions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have indicated that the cell membrane of Madin Darby Canine Kidney (MDCK) cells is hyperpolarized by a number of hormones and trace elements, in parallel with an enhancement of potassium selectivity. Without knowledge of the cell membrane resistance (R m), however, any translation of potassium selectivity into potassium conductance remains equivocal. The present study was performed to determine the R m of MDCK cells by cellular cable analysis. To this end, three microelectrodes were impaled into three different cells of a cell cluster; current was injected via one microelectrode and the corresponding voltage deflections measured by the other two microelectrodes. In order to extract the required specific resistances, the experimental data were analysed mathematically in terms of an electrodynamical model derived from Maxwell's equations. As a result, a mean R m of 2.0±0.2 kΩcm2 and an intercellular coupling resistance (R c) of 6.1±0.8 MΩ were obtained at a mean potential difference across the cell membrane of -47.0±0.6 mV. An increase of the extracellular K+ concentration from 5.4 to 20 mmol/l depolarized the cell membrane by 16.2±0.5 mV and decreased R m by 30.6±3.0%; 1 mmol/l barium depolarized the cell membrane by 20.1±1.1 mV and increased R m by 75.9±14.3%. Omission of extracellular bicarbonate and carbon dioxide at constant extracellular pH caused a transient hyperpolarization (up to −60.4±1.4 mV), a decrease of R m (by 75±4.5%) and a decrease of R c (by 23.1±8.4%). The changes in R m and R c were probably the result of intracellular alkalosis. Cadmium ions (1 μmol/l) led to a sustained, reversible hyperpolarization (to −64.8±1.3 mV) and to a decrease of R m (by 77.0±2.7%); mercury ions (1 μmol/l) cause a sustained hyperpolarization (to −60.1±1.2 mV) and a decrease of R m (by 76.3±3.9%). Neither manoeuvre significantly altered R c. We have previously shown that both cadmium and mercury hyperpolarize the cell membrane potential and increase its potassium selectivity; the decrease of the R m observed in the present study indicates that these effects are due to an increase of the potassium-selective conductance of the cell membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370765
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  • 5
    Electronic Resource
    Electronic Resource
    Ouabain decreases apparent potassium-conductance in proximal tubules of the amphibian kidney (1985)
    Springer
    Pflügers Archiv 404 (1985), S. 131-137 
    Details
    ISSN: 1432-2013
    Keywords: Ouabain ; Cell membrane potential ; Cell membrane resistance ; Potassium conductance ; Bicarbonate conductance ; Proximal tubule ; Amphibian kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract According to a previous study from this laboratory, the electrochemical gradient for potassium across the peritubular cell membrane of proximal tubules in the isolated perfused frog kidney increases following the application of ouabain. In order to test, if this phenomenon were due to a decrease of potassium conductance, the effects of ouabain on cell membrane resistances and the sensitivity of the peritubular cell membrane potential difference (PDpt) to step changes of peritubular potassium and bicarbonate concentration were studied. In the absence of ouabain, PDpt averaged −60±3 mV (n=25). A step increase of peritubular potassium concentration from 3 to 18 mmol/l (pH 8.07) depolarises PDpt (ΔPDk) by +24±2 mV (n=8). An increase of bicarbonate from 20 to 40 mmol/l (pH 8.07) hyperpolarises PDpt (ΔPDb) by −2.8±0.4 mV (n=9). The resistance of the luminal and peritubular cell membranes in parallel (R m) amounts to 45±9 kΩ cm (tubule length) (n=4) and the voltage divider ratio (VDR) to 1.4±0.2 (n=7). The resistance of the cellular cable (cellular core,R c) approaches 131±37 MΩ/cm (n=4). Peritubular application of 0.1 mmol/l ouabain leads to a gradual decline of PDpt (t 1/2 approx. 30 min), to an increase ofR m, a decrease of ΔPDk and an increase of ΔPDb. VDR andR c are not changed significantly. The data point to a functional link between the sodium/potassium ATPase and the potassium conductance of the peritubular cell membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585408
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of mepacrine, indomethacin, and nordihydroguaiaretic acid on the electrical properties of frog renal proximal tubules (1990)
    Springer
    Pflügers Archiv 416 (1990), S. 722-726 
    Details
    ISSN: 1432-2013
    Keywords: Proximal tubule ; Frog kidney ; Mepacrine ; Indomethacin ; Nordihydroguaiaretic acid ; Cell membrane resistance ; Cell membrane potential ; Phenylalanine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In proximal renal tubules of the frog kidney, stimulation of sodium-coupled transport leads to a depolarization of the peritubular cell membrane, followed by partial repolarization. These alterations of the potential difference across the peritubular cell membrane (PDpt,) are in part the result of altered peritubular potassium conductance. The repolarization has been blunted by the phospholipase A2 inhibitor mepacrine, but not by the cyclooxygenase inhibitor indomethacin. In the present study the effect of mepacrine, indomethacin and the lipoxygenase inhibitor nordihydroguaiaretic acid on the electrical properties of proximal renal tubules has been tested in the presence and absence of stimulated sodium-coupled transport. In the absence of inhibitors, addition of 10 mmol/l phenylalanine to the luminal perfusate leads to a rapid depolarization and partial repolarization of the peritubular cell membrane, a decrease of the luminal cell membrane resistance (R a) and a small increase of the cellular core resistance (R c). Removal of phenylalanine leads to rapid hyperpolarization, increase of R a and decline R c. Mepacrine (100 μol/l) depolarizes the cell membrane and increases the peritubular cell membrane resistance (R b), R c and the intracellular pH. In the presence of mepacrine, phenylalanine leads to a sustained depolarization and a transient decrease of R a. Indomethacin (10 μmol/l) does not significantly modify PDpt, the lumped resistance of both cell membranes (R m) or R c in the presence or absence of phenylalanine. Nordihydroguaiaretic acid (50 μmol/l) does not alter significantly PDpt, R a, R b or R c prior to phenylalanine. However, in the presence of nordihydroguaiaretic acid, the repolarization upon phenylalanine is significantly more rapid, and the removal of phenylalanine in the presence of nordihydroguaiaretic acid is followed by a significant decrease of both, R a and R b. The observations point to an involvement of eicosanoids in the regulation of ion conductances during stimulation of sodium-coupled transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370621
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