Suction electrode in frog heart ventricle: ANIMALS AND METHODS (part 3)

To measure MP, a floating microelectrode filled with 3 mmol/L KCl was placed inside the suction electrode. It was inserted repeatedly into a cell (Figure 1A, right). The reference electrode was placed in the suction capillary. Negative pressure, which varied from -5 to -40 kPa, was obtained in the suction electrode with a vacuum pump. MP and a0K were measured before, during and after each period of suction. Potassium equilibrium potential was calculated from the measured values of a0K as follows

where 58.0 mV is the Nernst coefficient for a temperature of 20°C; aiK represents an assumed value of 86 mmol/L for initial intracellular potassium activity ; Aa°K is the difference between the actual a0K and the extracellular a0K before suction; and f is the ratio of extracellular: cellular volume .
In some experiments the tip of the suction electrode was filled with Ringer’s solution containing tetrodotoxine 1.6×10-6 to 1.6X10-4 mmol/L, sucrose 200 mmol/L, 4-aminopyridine (4-AP) 20 mmol/L, tetraethylammonium (TEA) 40 to 80 mmol/L, verapamil 0.25 mg/L, LaCl3 0.1 to 1.0 mmol/L or Gd2O3 0.1 to 1.0 mmol/L. The drugs were applied 5 to 10 mins before introduction of negative pressure from -10 to -40 kPa. a0K and MP were measured before and during suction lasting 3 to 90 mins and after its release . Ultrastructure: The ultrastructure of the epicardium under a suction electrode was analyzed by routine electron microscopy . Histological material (epicardium beneath the suction electrode) was fixed with glutaraldehyde in phosphate solution, then with osmium tetroxide and embedded in Epon 812 (Fluka, Buchs, Switzerland). Slices were contrasted with lead citrate and examined under an electron microscope Jem 100 B (Jeol, Tokyo, Japan). You will always be able to find Generic Zyrtec shopping with a trusted foreign pharmacy.


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