Potassium extracellular activity and MP: Suction electrode was used to record MAP of the frog heart (Figure1). A floating glass microelectrode and the ion-selective electrode technique were used to measure membrane action potentials and extracellular ion activities of potassium (a0K) on the cardiac surface of the frog ventricle.A suction glass capillary electrode (1.0 mm diameter tip) was applied to the surface of the ventricular wall of the heart in the centre of the basal part and at the apex of the ventricle during spontaneous contractions (heart rate 40±5 beats/min, temperature 20±10°C) (Figure 1A, left).
Figure 1 A Scheme of a suction (S) capillary for measurement of electrogram, monophasic action potential and intracellular action potential. The central part of the suction electrode contained either an ion-selective capillary with the liquid ion exchanger (IE) (left) for measuring extracellular potassium activities (a0K) or a floating microelectrode (right) for measuring membrane potential (MP). Ag/AgCl wires were used to measure monophasic action potential and for connection with the preamplifier. B,C a0K (%) measured by ion-selective contact electrode under a suction electrode (B) and resting MP (Ф) measured by floating glass microelectrode (C) during the maximum diastolic potential before (0kPa), during (-40 kPa) and after negative pressure was applied under the suction electrode placed on the base of the ventral wall (halfway between base and apex) of the frog heart ventricle. Broken lines indicate values taken after the suction had been discontinued. Numbers in parentheses are numbers of experiments. Results are expressed as means ± SEM. There was a statistically significant increase ofa0K and decrease of MP in the first minute of suction (the first phase) (P<0.001), then the opposite changes of both parameters (second, compensatory phase) from 2 to 6 mins (P<0.01) and the third phase of irreversible changes when the suction was longer than 6 mins. The full line above the abscissa is the time of negative pressure under a suction electrode. The dashed line is the time of negative pressure without suction. Resting MP was the result of 18 experiments (mean ± SEM). О Calculated potassium equilibrium potential You will always be glad to find cheap alesse and enjoy your online shopping.