The cell membrane potential (PD) of Ehrlich ascites tumor cells was measured continuously at 37 degrees C with conventional microelectrodes during rapid alterations of extracellular fluid composition. At extracellular electrolyte composition mimicking the in vivo situation PD is -56.7 +/- 0.7 mV and the apparent membrane resistance is 62.2 +/- 2.2 M omega. Increasing extracellular potassium concentration from 5.4 to 20.0 mmol/l depolarizes the cell membrane by +18.4 +/- 0.5 mV. Thus, the transference number for potassium (tk, apparent slope potassium conductance over slope membrane conductance) is 0.53 +/- 0.01. A significant correlation is observed between tk and PD: tk = -(0.014 +/- 0.001) [1/mV] X PD [mV] -(0.243 +/- 0.051). 0.7 mmol/l barium depolarizes the cell membrane by +28.2 +/- 0.7 mV, increases the apparent membrane resistance by a factor of 2.6 +/- 0.1 and abolishes the apparent potassium conductance. Reduction of extracellular sodium concentration from 141 to 21 mmol/l depolarizes the cell membrane by +3.1 +/- 1.3 mV. Similarly, 0.1 mmol/l amiloride depolarizes the cell membrane by +3.3 +/- 0.7 mV. Reduction of extracellular chloride concentration from 128 to 67 mmol/l hyperpolarizes the cell membrane by -2.5 +/- 0.2 mV. 1 mmol/l anthracene-9-COOH does not significantly alter PD. Temporary omission of glucose from the extracellular fluid has no appreciable effect on PD. In conclusion, PD of Ehrlich ascites tumor cells is in the range of other mammalian epithelial cells and is generated mainly by potassium diffusion, while the conductances to sodium and chloride appear to be small.
The design and the application of a micro-enzyme-electrode for continuous monitoring of glucose concentration in the isolated tubule preparation is described. The principle of the electrode is the amperometric detection of hydrogen peroxide, which is a product of the oxidation of D-glucose by glucose oxidase immobilized at the tip of a micro-electrode. The resulting current causes a voltage deflection across a resistor in series with the electrode that is correlated directly with the glucose concentration. The electrode response to glucose is almost linear over the concentration range from 0 to 12 mmol/l with a slightly diminished slope in the higher range. Other sugars (12 mmol/l raffinose, galactose, fructose, sucrose, mannitol), pH (from 6.5 to 8.0) and pCO2 (from 1 to 10 kPa) do not influence the reading. A reduction of pO2 in the test solution to 1 kPa blunts the reading. Raising the temperature from 20 degrees C to 40 degrees C leads to a pronounced increase of the voltage deflection at a given glucose concentration. Interference is observed with strongly reducing agents such as L-cysteine, ascorbic acid and uric acid. At defined conditions the electrode is well suited to measure continuously glucose concentration in the luminal fluid at the collection site of the isolated perfused tubule of the kidney. Experiments are presented which illustrate the performance of the glucose electrode in this isolated tubule set-up. Peritubular reduction of potassium concentration or the application of ouabain diminish glucose reabsorption.
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