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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 1066 (1991), S. 111-114 
    ISSN: 0005-2736
    Keywords: (Necturus kidney) ; Basolateral membrane potential ; Hyperpolarization ; Membrane potential ; Organic acid ; Proximal tubule ; Sodium-potassium ion exchange ; pH effect
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0022-1910
    Keywords: Ion-selective microelectrodes ; K^+ transport ; Malpighian tubules ; Transmembrane gradients
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Insect Physiology 38 (1992), S. 431-446 
    ISSN: 0022-1910
    Keywords: K^+ transport ; Malpighian tubules ; luminal perfusion ; microelectrode study ; resistance measurements
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0022-1910
    Keywords: Ba^2^+ ; DNP ; H^+-gradient ; Ion-selective microelectrodes ; K^+-gradient ; Malpighian tubules
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0022-1910
    Keywords: Ant ; Antidiuretic factors ; Diuretic factors ; Fluid secretion ; Malpighian tubule
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 412 (1988), S. 369-375 
    ISSN: 1432-2013
    Keywords: Renal proximal tubule ; Necturus ; Peritubular membrane potential ; Transepithelial membrane potential ; Potassium apparent transference number ; Alkalinization ; Barium ; Bicarbonate free
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Short-term peritubular alkalinization from 7.5 to 8.5 hyperpolarized (−8.8 mV) the basolateral membrane potential (V 1) in HCO 3 − free Hepes buffered Necturus renal proximal tubule cells. This sustained base induced hyperpolarization (BIH) was associated with an increase in the peritubular apparent transference number for potassium ( $$t_{K^ + } $$ ). The apparent transference number for potassium ( $$t_{K^ + } $$ ) was estimated at pH 7.5 and 8.5 by raising peritubular K+ from 2.5 to 10 mmol/l. $$t_{K^ + } $$ increased linearly asV 1 hyperpolarized, whereas $$t_{K^ + } $$ measured in the presence of peritubular Ba2+ at pH 7.5 and 8.5 was nearly zero. However, the BIH persisted in the presence of barium at the peritubular, luminal or both sides of the epithelium. Moreover this BIH was also accompanied by a small hyperpolarization (−0.4 mV) of the transepithelial membrane potential (V 3) in the absence or presence of peritubular and/or luminal Ba2+. Therefore we conclude that BIH must originate from additional mechanisms other than an increase in peritubular or luminal potassium conductance.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2013
    Keywords: Blood perfusion Isolated rabbit kidney Functional state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. This report describes the technique and procedure for perfusing an isolated rabbit kidney with 25 ml heparinized autologous blood in a closed circuit including a pump and an oxygenator. The duration of the operative ischaemia was 5–8 min; the perfusion lasted 2.5 hours. An additional infusion was made to compensate for urinary losses. Renal blood flow increased progressively from 2.01±0.1 to 2.65±0.22* ml/g kidney weight (kw) per min (*P〈0.05). Between the first (P1) and the last (P4) urine collection period the glomerular filtration rate (GFR) fell from 288±25 to 217±38* µl/g kw per min, urine flow from 5.58±1.13 to 4.91±0.75 µl/g kw per min, Na+ excretion from 1.07±0.19 to 0.63±0.12* µmol/g kw per min, K+ excretion from 0.46±0.03 to 0.28±0.05* µmol/g kw per min, P excretion from 2.5±0.2 to 2.0±0.5 µg/g kw per min, Ca excretion from 0.4±0.1 to 0.12±0.05* µg/g kw per min, creatinine excretion from 6.94±0.32 to 5.68±0.54 µg/g kw per min, glucose excretion from 18.2±3.2 to 1.6±0.5* µg/g kw per min, the free water clearance (CH2O) from –6.57±0.85 to –5.10±1.31 µl/g kw per min and urine osmolality from 600±52 to 590±105 mOsm/kg, urea excretion from 0.75±0.16 to 0.95±0.13 µmol/g kw per min. Excretion of glucose, P or Ca was observed only above a given plasma threshold value, and no transport maximum was found for glucose or P. Ca reabsorption paralleled the Na reabsorption. The proximal tubule pressure, measured within the 1st h of perfusion, was 12.5±1.1 mm Hg. Histological examination at the end of the perfusion showed dilatation of the tubules as in the non-perfused kidneys, and the presence of numerous bacteria. Hypertonic urine (380–1110 mOsm/kg) was observed in the presence of vasopressin, in the latter's absence the urine was hypotonic urine (206–278 mOsm/kg). There was no correlation between renal plasma flow and the GFR. CH2O increased with increasing filtered Na+ load. In conclusion, the blood-perfused, isolated rabbit kidney has a fairly constant functional capacity for approximately 2 h.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2013
    Keywords: Malpighian tubule ; Formica ; Electrophysiology ; Cable analysis ; Dinitrophenol ; Protonophore
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In Formica Malpighian tubules KCl secretion is driven by a V-type H+ ATPase in the luminal membrane in parallel with a H+/K+ antiporter. The effect of the protonophore dinitrophenol (DNP) was investigated on the isolated, symmetrically perfused tubule. DNP was applied in two different concentrations: 0.2 mmol/l and 1 mmol/l. The effects were fast and rapidly reversible. The equivalent short-circuit current (I sc) was reduced significantly to respectively 25±3% Cn=4) and −3±7% (n=11) of the control value when 0.2 mmol/ l or 1 mmol/l was added to the bath. When 1 mmol/l DNP was applied the transepithelial resistance (R te) decreased significantly to 74±11% of the control value (n=11), and the luminal over basolateral voltage divider ratio (VDR), providing an estimate of luminal over basolateral membrane resistance, decreased to 37±12% of the control (n=6). A concentration of 1 mmol/l DNP was also applied from the lumen. The decrease in I sc was significant, but much less pronounced (74±5% of control; n=6) and no significant changes in R te and VDR were observed. It is argued that, when the concentration in the bath is high enough, DNP may cross the cell and have a protonophoric effect not only on the mitochondria but also across the luminal cell membrane explaining the drop in transepithelial and in relative luminal membrane resistance. The diminished effectiveness of DNP, when applied from the luminal side, suggests that the luminal membrane is somehow less permeable to toxic substances, but that DNP very rapidly enters the cell via the basolateral membrane and may bring about an initial protonophoric effect across this membrane.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-4994
    Keywords: Ratiometric ion indicators ; Fura-2 ; calibration equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The absolute values of intracellular ion concentrations as monitored by specific fluorescent indicators are determined by using calibration curves obtained underin vitro andin vivo conditions. In the derivation of the calibration curve by Grynkiewicz et al [(1985)J. Biol. Chem 260, 3440] it is implicitly assumed that the observed fluorescence signal is directly related to the concentrations of the free dye and the dye-ion complex in the ground state. We modified the calibration equation so that ion binding and dissociation in the excited state are taken into account. The extended calibration equation assumes the knowledge of the rate constants in the excited state. Expressions for the calibration curve assuming the absence or presence of an excited-state reaction are compared for the Ca2+ indicator Fura-2. The excited-state rate constants are determined by global compartmental analysis of time-resolved fluorescence decays of Fura-2 collected at various excitation and emission wavelengths using different Ca2+ concentrations. It is found that for Fura-2 there is negligible interference of the excited-state reaction so that the original calibration can used.
    Type of Medium: Electronic Resource
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