The Effect of Stimulation Frequency on the Ionic Currents in Single Atrial Cells of the Rabbit

In single atrial cells isolated from rabbit hearts the calcium current and [Caj-dependent transient outward current were recorded using the whole-cell clamp technique and the effect of stimulation frequency on these currents was investigated. Voltage dependent transient outward current, which contributes the initial, rapid repolarization phase of the action potential and is frequency-dependent, was also investigated. Increasing the stimulation frequency from O. 025 Hz to 1 Hz had no effect on the calcium current and [Caj-dependent transient outward current and greatly inhibited voltage-dependent transient outward current. The amplitude of voltage dependent transient outward current increased as the membrane potential became depolarized, its steady-state inactivation spans the voltage range -70 mV to -10 mVand steady-state activation curve -30 mV to 30 mV. Within the range of the resting membrane potential (at -70 mV), the voltage-dependent recovery time constant was 1. 3 s. The reversal potential was about -50 mV. Voltage-dependent transient outward current was inhibited by K-channel blockers and not inhibited by modulation of [Cali. From the above findings, it is concluded that due to the amplitude and voltage-dependent recovery time constant which were the basic mechanisms for frequency-dependency, the voltage- dependent transient outward current contributes the initial, rapid repolarization phase and changed the action potential configuration according to stimulation frequency in the rabbit atrium

세포의 NA+농도 변화가 기니피그 위 평활근 서파에 미치는 영향

The characteristics of contractile and electrical responses to various concentrations of extracel1ular sodium in the antrum of guinea-pig stomach were investigated in order to elucidate the mechanisms generating and control1ing the slow wave which is known to be responsible for the gastric motility. The results obtained were as fol1ows: 1) Tonic contraction increased as the concentration of extracel1ular sodium decreased. However, phasic contraction gave a different response around 10 mM Na +. 2) In Na + -deficient solutions, prolongation in the second component and potentiation in the spike component of the slow wave and membrane depolarization were observed, Those changes became more marked with each decrement of Na + concentration. 3) In solutions below 10 mM Na +, small slow waves whose components could not be clearly distinguished appeared at a faster frequency than it did in normal Tyrode solution. 4) In the presence of guanethidine and atropine the change described in 3) disappeared in solutions of Na + concentration below 10 mM. Instead the same responses as described in 2) were observable, From the above results following conclusions can be made: As the concentration of extracel1ular sodium decreases the configuration of the slow wave of the antral smooth muscle in guinea-pig stomach changed markedly, showing prolongation in the second component, potentiation in the spike component and depolarization in the membrane potential. These results are direct effects of extracellular sodium on the smooth muscle cell membrane. However, in low sodium concentration below about 10 mM, the influence of autonomic nervous system on the slow wave becomes remarkable and above changes of the slow wave cannot be found

ReIationship of Plasma Potassium and Hydrogen Ion Concentrations in Acidosis-Induced HyperkaIemia and HyperkaIemia-Induced Acidosis

The relationship between the plasma potassium concentration and blood pH was evaluated in acidosis-induced hyperkalemia and hyperkalemiainduced acidosis in rabbits. In the first group of animals, metabolic acidosis was induced by an intravenous infusion of 0.1 N hydrochloric acid, and in the second group, hyperkalemia was induced by an intravenous infusion of 20 mM potassium chloride solution. The third group of animals was infused with both hydrochloric acid and potassium chloride. All three groups showed metabolic acidosis, hyperkalemia, and compensatory respiratory alkalosis. The degree of alkalosis was most extensive in HCl infused, and least in KCl infused animals. The simultaneous infusion of HCl and KCl induced the most extensive change in the acid-base status, and the hydrogen and potassium ion concentrations. However the quantitative relationship between potassium and hydrogen ion concentrations was similar in all three groups. It is, therefore, presumed that acidosis-induced hyperkalemia and hyperkalemia-induced acidosis involve a common mechanism

결장뉴와 위 유문동에서 K-제거 경축에 대한 세포밖 Na의 영향

To study the role of Na-Ca exchange mechanism which controls the intracellular free Ca concentration, the changes in contractile force and membrane potential of G-I smooth muscle were measured. Guinea-pig's taenia coli and gastric antrum were isolated, and all experiments were performed in Tris-buffered Tyrode solution aerated with 100'10 O2 and kept 35"C. After application of K-free solution which is known to increase the intracellular Na concentration due to inhibition of Na-K pump, Na-free or low Na solution were applied. Contractions were recorded with force transducer, and membrane potentials were measured by single sucrose-gap method. In the taenia coli, the extent of relaxation of K-free contracture was inversely proportional to external Na concentration. As the external Na concentration was decreased, the membrane potential was more hyperpolarized. In the gastric antrum, the extent of relaxation of K-free contracture increased proportionately to the decrease of external Na concentration. Membrane potential was maximally hyperpolarized at Na-free solution. As extracellular Na concentration was increased, the degree of hyperpolarization decreased, and at 125 mM Na the membrane potential was depolarized. When Ca antagonist (verapamil) was applied, K-free contracture did not develop in the taenia coli. It is concluded that Na-Ca exchange mechanism would play little role in the control of intracellular free Ca concentration in the taenia coli and gastric antrum. ; Na-Ca 교환 기전이 평활근의 세포내 칼슘 이온 농도 조절에 기여하는 정도를 연구하기 위하여 위장관 평활근의 수축과 세포막전압의 변화를 관찰하여 분석하였다. auinea-pig의 결장뉴와 위 유문동을 적출하여 35℃에서 100% 산소로 평형을 이룬 Tris-완충 Tyrode 용액에서 이들 조직이 일정한 빈도와 크기로 자발적 수축을 하게 되면 세포내 Nashd도를 증가시키는 K-제거 용액(K-free Tyrode solution)으로 전처치하여 K-제거 경축을 유발시키고 여기에 Na-제거 용액과 여러 수준의 Na 농도 용약을 관류시켜 수축곡선의 변화를 기록하였다. 단일 자당액 간극법(single sucrose-gap method)으로는 세포막전압 변화를 기록 분석하여 다음과 같은 결과를 얻었다. 1. 결장뉴에서 K-제거 경축이 이완되는 정도는 세포밖 Na 농도에 반비례하였다. 2. 결장뉴에서 세포밖 Na 농도가 높을수록 과분극되는 정도가 적었다. 3. 유문동에서도 결장뉴처럼 K-제거 경축이 Na-제거 용액에서 이완되었고, 세포밖 Na 농도를 증가시키면 K-제거 경축을 이완시키는 정도가 작아졌고, 세포막전압이 과분극되는 정도도 세포밖 Na 농도가 높을수록 작았다. 4. Ca 억제제인 varapamil을 1mg/l 전처치하면 K-제거 경축이 거의 생기지 않았다. 이상의 결과로 보아 결장뉴와 위 유문동에서는 세포내 칼슘 이온농도 조절에 Na-Ca 교환 기전의 역할이 중요하지 않는 것으로 생각된다

방실결절의 세포막 이온전류에 관한 연구

The rabbit AV node was isolated and dissected into small strips of 0.3 mm width to apply two microelectrode voltage clamp technique. Then, slow inward current (isJ, hyperpolarization activated inward current (if) and pump current were recorded and their kinetic properties were analysed. The results obtained were as follows: 1. The isolated AV node continued to beat, but the rate was slower than that in the SA node. The configuration of action potential showed regional difference. Small AV node preparations also showed spontaneous action potentials whose configurations were similar to those in the SA node. Resting membrane potential was about -40 mV. 2. On depolarization from the holding potential of -40 mV to various potential level, slow inward current (isf) was recorded. It was disappeared by adding 2 mM Mn+ + and increased remarkably by 10-6M adrenaline. Current-voltage relationship, steady-state inactivation and recovery from inactivation were also studied and considered similar to those in other cardiac tissues. 3. In response to hyperpolarizing voltage clamp pulse, the current if was activated. The reversal potential was about -25 mV. 0.5 mM Cs" decreased if in a voltage-dependent manner. 10-6M adrenaline showed little effect on if. 4. The activity of electrogenic Na+ pump was demonstrated by K+ -induced transient outward current or transient hyperpolarization after pre-treatment with K+-free Tyrode solution. The pump activity was affected by duration of pre-treatment, K+ concentration in recovery solution and Ca + + concentration in K+ -free Tyrode solution

The Effect of Changes in the Separation Process for the Performance of Recycled Cement Powder: A Comparison with a Previous Study for Radioactive Waste Immobilization

Separation of hydrated cement paste from aggregate is a key technology to reduce the amount of radioactive concrete waste during the decommissioning process. If separated cement-paste portions can be recycled as a solidifying agent for other radioactive waste, the amount of radioactive concrete waste could be close to “zero”. A study was conducted to achieve circular economy in the area of concrete decommissioning and found it to be successfully used as a solidifying agent for immobilization of liquid radioactive waste. However, previous work used a process that requires large amounts of energy (heat treatment was applied to most of the concrete fraction) because the objective was to completely remove hydrated cement powder from the aggregate. In this work, the separation system was modified to increase energy efficiency (heat treatment was applied to separated powder only), but such a change decreased the surface area of the recycled cement powder due to a higher inclusion of aggregate powder. A relatively lower solution to binder ratio could have been achieved for the preparation of wasteform specimens, and as a result, a 28 day compressive strength of wasteform could have become higher, but the final leachability indices were lower than the results observed from previous work. The results from 28 day compressive strength, thermal cycling and 90 day leaching experiments met the acceptance criteria for wasteform, indicating that this modified system can also be used for immobilization of liquid radioactive waste to meet the “zero” production of concrete waste during the decommissioning of a nuclear power plant. It should be noted that accurate monitoring of aggregate content in recycled cement powder during production is important to maintain proper reactivity of recycled cement powder