Archive for the ‘Cardiology’ Category

Suction electrode in frog heart ventricle: DISCUSSION (part 4) / buy flovent inhaler

 On the other hand, when tetrodotoxin was present or sucrose was substituted for sodium ions in the tip of the suction electrode (elimination of sodium channels), MAP development was suppressed. This indicates that suction reversibly increases the probability of sodium channel opening. The influx of sodium into the cells might then cause potassium efflux into the extracellular space. Calcium fluxes are evidently not so important because inhibition of main calcium sources – sarcolemmal L-type calcium channel by verapamil and La3+ – influenced the time course of changes in MAP only slightly and did not influence MAP amplitude. Read the rest of this entry »

Suction electrode in frog heart ventricle: DISCUSSION (part 3) / cheap asthma inhalers

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According to Peter and Antoni , suction increases conductance of the tissue under the suction electrode, which means that action potentials and other currents at the site of negative pressure are sensed by the suction electrode, similar to a standard intracellular electrode. It is not surprising that the time course and relative amplitudes of individual components of the suction-evoked MAP and intracellularly recorded action potentials are very similar. The question then arises as to which types of ion channels are involved. Are the stretch-activated nonspecific cationic channels or other channels responsible for the increase of myocyte permeability during suction, the pseudointracellular appearance of MAP, and the increase of extracelluar potassium and intracellular calcium concentrations ? The internet’s most trusted pharmacy is looking forward to having you among its customers: just see how cheap and easy it can be for you to get cheap asthma inhalers without any kind of prescription and start your shopping being sure you are protected every time.
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Suction electrode in frog heart ventricle: DISCUSSION (part 2)

The origin of MAP has not yet been explained sufficiently. Former ideas were based on ‘discharging’ of the membrane potassium battery by an increase of potassium permeability during the introduction of positive or negative pressure . This view accounted only for electrical changes and did not take into account mechanical changes such as stretching of tissue and of the cell membrane in particular .
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Suction electrode in frog heart ventricle: DISCUSSION (part 1)

Suction electrode in frog heart ventricle: DISCUSSION  (part 1)

DISCUSSION

In our study, MAP developed in the ventricular region under a suction capillary, and the resting MP decreased in parallel with a rise of a0K up to 11 mmol/L. a0K and MP changed similarly in three phases, and these changes were reversible as long as suction at -40 kPa did not last longer than a few minutes. The second phase of the compensatory decrease of a0K was suppressed by cooling of the tissue to 2°C and by ouabain, and was absent if the ventricle was arrested. Read the rest of this entry »

Suction electrode in frog heart ventricle: RESULTS (part 5)

Sarcolemmal Na+/K+-ATPase activity and density of Houabain binding sites: Sarcolemmal Na+/K+-ATPase activity and density of [3H]ouabain binding sites were measured because the second phase of compensatory decrease in a0K differed among the base, middle and apex during suction (Figure 4). Sarcolemmal vesicles were prepared from the apical, middle and basal thirds of the frog ventricle. Maximum Na+/K+-ATPase activity and density of [3H]ouabain binding sites were measured. Both parameters were higher at the base than at the apex (P<0.01) (Table 2).
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Suction electrode in frog heart ventricle: RESULTS (part 4)

 frog heart ventricle: RESULTS (part 4)

His may indicate that this partial or even full recovery of elevated extracellular a0K is caused by active pumping of potassium ions from the extracellular space into the myocytes by membrane ouabain-sensitive Na+/K+-ATPase . If this view is correct, inhibition of Na+/K+-ATPase by cooling or by ouabain would prevent this compensatory phase of the transient a0K during suction. Cooling the heart to 2°C or adding ouabain (10-6 mol/L) to the Ringer’s solution for 5 to 10 mins suppressed the second phase of compensatory a0K decrease under the suction electrode during negative pressure (Figure 5).
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Suction electrode in frog heart ventricle: RESULTS (part 3)

frog heart ventricle: RESULTS (part 3)

Maximum diastolic a0K was approximately 5 mmol/L. It changed simultaneously with MP changes (Figure 1B, P<0.01) and followed the same time course and reversibility pattern. Maximum values up to 11 mmol/L were observed during maximum depolarization (P<0.001). The calculated potassium equilibrium potentials, based on actual values of a0K, were close to the real MP measured with the glass microelectrode (Figure 1C) .
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