Effects of sodium, potassium and chloride ions on the membrane potential of Valonia aegagropila

Changes of the resting potential of Valonia cell in sea wateragainst a 10-fold increase of the external concentrations ofK^$, Na^$ and Cl^– were 1±1, 6.2±0.1 and 38.9±4mV, respectively. The potassium conductance was smaller than7 µ/cm², while the Na and Cl conductances were 45 and281 µ/cm², respectively, in normal sea water. The positivevacuolar potential could be explained by these ionic conductances.On the other hand, the membrane became more sensitive to K^$,if the cell was incubated for about 30 min in K-rich (100 mM)sea water. It is worth noting, however, that the membrane conductancewas lower in the K-rich sea water than in the normal sea water. (Received October 7, 1974; )     

Intracellular activities of chloride, potassium and sodium ions in rabbit corneal epithelium

The mechanism of ion transport in the epithelium of rabbit cornea was studied by determining the intracellular ion activity of Cl-, Na+ and K+ under various conditions. Ionic activities were measured by means of microelectrodes containing liquid ion-exchangers selective for Cl-, Na+ or K+. The Cl- activity in basal cells of the epithelium in Na+ containing bathing solutions amounts to 28 +/- 2 mM (n = 11). This value is 1.9-times greater than expected on the basis of passive distribution across the tear side membrane. This finding suggests the existence of a Cl- accumulating process. Replacement of Na+ in the aqueous bathing solution by choline or tetraethylammonium results in a reversible decrease in Cl- activity to 22 +/- 1 mM (n = 11, P less than 0.025). The ratio of observed and predicted Cl- activity decreased significantly from 1.9 to 1.4 (P less than 0.05). The decrease in Cl- activity due to Na+ replacement was rather slow. In contrast, after readmittance of Na+ to the aqueous bathing solution, Cl- activity rose to a stable level within 30 min. These results indicate involvement of Na+ in Cl- accumulation into the basal cells of the epithelium. The K+ and Na+ activities of the basal cells of rabbit corneal epithelium in control bathing solutions were 75 +/- 4 mM (n = 13) and 24 +/- 3 mM (n = 12), respectively. The results can be summarized in the following model for Cl- transport across corneal epithelium. Cl- is accumulated in the basal cells across the aqueous side membrane, energized by a favourable Na+ gradient. Cl- will subsequently leak out across the tear side membranes. Na+ is extruded again across the aqueous side membrane of the epithelium by the (Na+ + K+)-ATPase.     

Effect of ammonium,sodium, and potassium ions on rabbit muscle phosphofructokinase-1 and adenylate kinase activities

This report shows that 30 nM PFK-1 and 30 nM AK were both affected by the presence of NH₄⁺, Na⁺, and K⁺ salts but with opposite consequences. Low concentrations of PFK-1 lose about half of its activity as a result of dilution and become susceptible to further activity losses owing to the presence of monovalent salts. On the other hand low concentrations of AK lose about 75 percent of its activity but regains activity losses owing to the presence of monovalent salts. It was determined that regain of AK activity did not appear to be a reflection of a major effect on the K_m value of either AMP or ATP. Dilution to 30 nM AK resulted in no increase K_m values compared to K_m values at 140 nM AK. Dilution caused major decreases in the maximum velocities, V_max, when ATP or fructose 6-phosphate was the variable substrate. It was shown in earlier reports that these same low concentrations of PFK-1 and AK were susceptible inhibitions by ascorbate. These attributes are discussed as they may relate to the role of ascorbate facilitation glycogen synthesis in resting muscle and the role that the cytoskeleton infrastructure scaffold may play is also discussed.     

Modulation of brain S2 serotonin receptors by lithium, sodium and potassium chloride

The effect of LiCl, NaCl, and KCl on serotonin competition for 3H-ketanserin binding to S2 serotonin receptors in homogenates of rat prefrontal cortex were investigated. LiCl was the most potent of the ionic modulators in lowering the apparent affinity of serotonin for the S2 serotonin receptor. A threshold effect was noted at 12 mM LiCl (a 60% change in IC50); at 120 mM LiCl a nine-fold shift in the serotonin IC50 was noted. 120 mM NaCl or KCl demonstrated similar effects as 12 mM LiCl in reducing serotonin's apparent affinity. These results indicated that monovalent cations modulate S2 serotonin receptor affinity for serotonin and that lithium ion is more potent than sodium or potassium.     

Effects of sodium chloride stress and calcium supply on growth, potassium uptake, and internal chloride and sodium levels of winter wheat seedlings

The effects of saline conditions on the K+ (86Rb), Na+ and Cl- uptake and growth of 6-day-old wheat (Triticum aestivum L. cv. GK Szeged) seedlings were studied in the absence and presence of Ca2+. It was found that on direct NaCl treatment the K+ uptake of the roots in the absence of Ca2+ declined significantly with increasing salinity. The reverse was true, however, in the case of NaCl pretreatment: seedlings grown under highly saline conditions (50 mM NaCl) absorbed more K+ than those pretreated with low levels of NaCl (1 or 10 mM NaCl). The data indicate a definite Na(+)-induced K+ uptake inhibition and/or feed-back regulation in the K+ uptake of roots under the above-mentioned growth conditions. As regards the Ca2+ effect, it was established that supplemental Ca2+ counteracts the unfavourable effect of saline conditions as concerns both the K+ uptake of the roots and the dry matter yield of the seedlings. The internal concentrations of Na+ and Cl- in the seedlings increased in proportion to increasing salinity. Marked differences were experienced, however, in the internal concentrations of Na+ and Cl- in the roots and shoots, respectively. It was concluded that under these experimental conditions the salt tolerance of wheat could be related to its capability of restricting the transport of Na+ at low and moderate levels to the shoots, where it is highly toxic.     

Effects of hypoxia on plasma concentrations and daily elimination of sodium, potassium and chlorine ions

Serum concentrations of Na+, K+ and Cl- are studied, as well as the elimination of these ions in urine, in patients suffering from chronic respiratory insufficiency, being classified in two groups according to the level of hypoxemia: group A (PO2 less than 6.66 KPa) and group B (PO2 less than 8 KPa). A third group C of healthy patients with analogous anthropological characteristics has served as a control group. The concentrations of serum of the three ions are noticeably similar in the three groups, but the daily elimination of Na+, K+ and Cl- is less in those suffering from respiratory insufficiency than in those of the control group, with significant statistical differences in all cases except with K+ in those suffering from pronounced hypoxemia. On analysing the correlation between the rates of elimination of ions in urine, with the plasmatic values of PO2, PCO2 and [H+] of all the patients studied, the highest values of the Pearson coefficient are found on correlating the elimination of ions with the partial pressures of oxygen, therefore suggesting that hypoxia could be the main motor inducing metabolic changes.     

Quantitative description of sodium and potassium currents and computed action potentials in Myxicola giant axons

All analysis of the sodium and potassium conductances of Myxicola giant axons was made in terms of the Hodgkin-Huxley m, n, and h variables. The potassium conductance is proportional to n². In the presence of conditioning hyperpolarization, the delayed current translates to the right along the time axis. When this effect was about saturated, the potassium conductance was proportional to n³. The sodium conductance was described by assuming it proportional to m³h. There is a range of potentials for which τ_h and h_∞ values fitted to the decay of the sodium conductance may be compared to those determined from the effects of conditioning pulses. τ_h values determined by the two methods do not agree. A comparison of h_∞ values determined by the two methods indicated that the inactivation of the sodium current is not governed by the Hodgkin-Huxley h variable. Computer simulations show that action potentials, threshold, and subthreshold behavior could be accounted for without reference to data on the effects of initial conditions. However, recovery phenomena (refractoriness, repetitive discharges) could be accounted for only by reference to such data. It was concluded that the sodium conductance is not governed by the product of two independent first order variables.     

Rates of efflux and intracellular concentrations of potassium, sodium and chloride ions in isolated fat-cells from the rat

1. The metabolism of K(+), Na(+) and Cl(-) has been investigated in isolated fat-cells prepared from the epididymal adipose tissue of rats. 2. Methods are described for measuring the intracellular water space, the rates of loss of intracellular (42)K(+), (22)Na(+) and (36)Cl(-) and the intracellular concentrations of K(+), Na(+) and Cl(-) in isolated fat-cells. 3. The intracellular water space, measured as the [(3)H]water space minus the [carboxylic acid-(14)C]inulin space, was 3.93+/-0.38mul./100mg. cell dry wt. 4. The first-order rate constants for radioisotope effluxes from isolated fat-cells were 0.029min.(-1) for (42)K(+), 0.245min.(-1) for (22)Na(+) and 0.158min.(-1) for (36)Cl(-). 5. The intracellular concentrations of K(+), Na(+) and Cl(-) were 146m-equiv./l., 18.6+/-2.9m-equiv./l. and 43+/-2.4m-equiv./l. respectively. 6. The total intracellular K(+) content of isolated fat-cells was determined by atomic-absorption spectrophotometry to confirm the value obtained from the radioisotope-efflux data. 7. The ion effluxes from isolated fat-cells were: K(+), 1.5pmoles/cm.(2)/sec., Na(+), 1.6pmoles/cm.(2)/sec., and Cl(-), 2.4pmoles/cm.(2)/sec. 8. The membrane potential of isolated fat-cells calculated from the Cl(-) distribution ratio was -28.7mv.     

Effect of potassium and ammonium ions upon glycolysis catalyzed by an extract of rat brain

The stimulatory effect of ammonium and potassium ions upon glycolysis, as catalyzed by an extract prepared from an acetone powder of rat brain, has been investigated. The effect is most pronounced when small amounts of adenosine triphosphate (ATP) are employed and it becomes progressively less apparent as the ATP concentration is increased.Unlike the extracts and homogenates obtained from fresh brain tissue (1,2), glycolysis by the acetone extracts is not inhibited significantly by sodium ion. This is apparently due to the low apyrase content of these extracts. In addition the experiments indicate that the NH₄⁺ and K⁺ have direct stimulatory effects which are not due to antagonism between Na⁺ and NH₄⁺ or K⁺. This suggestion gains credence by the observation that the same concentration of NH₄⁺ is required for stimulation whether or not the concentration of Na⁺ is reduced through substitution of trishydroxymethylaminomethane buffer for the NaHCO₃ buffer. Apparently NH₄⁺ and K⁺ serve to maintain ATP in these systems by initiating or accelerating phosphorylation reactions. In so doing, they prevent the formation of adenylic acid which is fairly rapidly dephosphorylated in those systems by a 5-nucleotidase.     

Effect of sodium,potassium, and calcium ions on electroreceptor function in catfish

Impulses from single electroreceptors (small pit organs) of catfish (Ictalurus nebulosus) were recorded during stimulation by square pulses. Solutions with different concentrations of potassium, sodium, and calcium ions were applied to the pore of the receptor. Solutions with a low CaCl₂ concentration did not alter the responses of the receptor. Calcium ions in concentrations of over 5 mM increased the threshold of the response to electrical stimulation. The threshold to anodal stimulation was increased in solutions of 2 mM sodium and potassium and no response was given to a cathodal stimulus. The effect of 2 mM solutions of NaCl and KCl was abolished by the addition of 0.4 mM CaCl₂ or by application of a long anodal stimulus of high intensity (10⁻⁸∓10⁻⁷ A/mm²). Increasing the potassium ion concentration to 10–20 mM restored normal receptor function but a further increase led to elevation of the threshold. The action of an electric current is compared with the action of the ions.     

Glutamate, calcium ion-chelating agents and the sodium and potassium ion contents of tissues from the brain

1. Salts of l-glutamate added to cerebral tissues maintained in glucose-saline-bicarbonate solutions cause the Na(+) content of the tissues to increase rapidly and K(+) to be lost. Entry of (22)Na(+) also is accelerated by l-glutamate and this acceleration is inhibited by low concentrations of tetrodotoxin. 2. Tissue Na(+) content and its rate of increase after the addition of l-glutamate are affected by the Ca(2+) of incubation media. 3. Very rapid and extensive entry of Na(+) to the tissue is caused by EDTA, and a moderate entry by citrate and ATP. Calculations of the concentration of free Ca(2+) in media after these additions indicate that Na(+) entry is sometimes associated with low Ca(2+) concentration, but that other substances, especially l-glutamate, act without greatly diminishing Ca(2+) concentration. 4. Experiments with 2,4-dinitrophenol and valinomycin are also reported and aspects of the Na(+) entry formulated and discussed.     

血小板活化因子对豚鼠心室肌细胞动作电位和钾通道的影响

应用全细胞膜片钳技术研究了血小板活化因子(platelet activatingfactor,PAF)对豚鼠心室肌细胞动作电位和钾电流的影响.结果发现,当电极内液ATP浓度为5 mmol/L(模拟正常条件)时,1 μmol/L PAF使APD90由对照的225.8±23.3 ms延长至352.8±29.8ms(n=5,P＜0.05);使IK尾电流在指令电压 30 mV由对照的173.5±16.7 pA降至152.1±11.5 pA(P＜0.05,n=4);使Ikl在指令电压为-120 mV时由对照组的-6.1±1.3 nA降至-5.6±1.1 nA(P＜0.05,n=5);但PAF在生理膜电位范围(-90mV～ 20mV)对IK1没有影响.当电极内液ATP浓度为0mmol/L时,IK·ATP开放(模拟缺血条件),1 μmol/LPAF却显著缩短APD90,由对照的153±24.6 ms缩短至88.2±19.4 ms(n=5,P＜0.01).而用1 μmol/L格列本脲(IK·ATP的特异阻断剂)预处理后,恢复了PAF可显著延长动作电位时程的作用.结果提示,PAF可能扩大缺血心肌和正常心肌细胞动作电位时程的不均一性,是缺血/再灌注性心律失常发生的重要原因.     

The relationship between sodium,potassium, and chloride in amphibian muscle

The Na,⁺ Cl^-, and K⁺ content of toad plasma and the sartorius muscle has been determined. Although the Na⁺ and Cl^- level of the muscles in the living animal varied greatly (0 to 38.0 m.eq. per kg., and 0 to 31.8 m.eq. per kg. respectively) the K⁺ level was subject to a smaller variation (76.5 to 136 m.eq. per kg.). There was a direct relationship between Na⁺ and Cl^-, which was independent of the K⁺ level. There is a closely related gain of Na⁺ and Cl^- when muscle is soaked in normal Ringer. These gains are not related to the K⁺ loss, frequently found on soaking. The relationship between the three ions was studied in a large series of 124 muscles in normal Ringer. As found in vivo, there was a correlation between Na⁺ and Cl.^- This correlation was independent of K⁺ content, except when this was abnormally low. Alteration of the external NaCl level produced concomitant changes in the internal levels of these ions. Alteration of the external KCl level produced an increase in internal Cl^- similar to that found with high NaCl solutions, but the amount of K⁺ entering the cell was approximately one-third of the external increase. Removal of K⁺ from the external solution did not result in a loss of K⁺ from the cell, although there was an adequate amount of Cl^- present to accompany it. The results cannot be reconciled with either a Donnan concept for the accumulation of K⁺, or a linked carrier system. A theory is proposed to account for the ionic differentiation within the cell. The K⁺ is assumed to be adsorbed onto an ordered intracellular phase. The normal metabolic functioning of the cell is necessary to maintain the specificity of the adsorption sites. There is another intracellular phase, which lacks the structural specificity for K⁺, and which contains Na⁺, Cl^-, and K⁺ in equilibrium with the external solution. The dimensions of the free intracellular phase will vary from cell to cell, but it will be smaller in the intact animal, and will increase on soaking in normal Ringer, until it is approximately one-third of the total cellular volume. The increase in this phase may be ascribed to a decrease in the energy available to maintain the ordered phase.     

Effects of intracellular sodium and potassium iontophoresis on membrane potentials and resistances in toad urinary bladder

Conclusion The elastic X-ray/neutron diffraction techniques described in this review are currently capable of providing substantial information concerning the time-averaged structures and intermolecular ordering of molecular components within a dynamic membrane structure. In addition, the time resolution of the elastic X-ray diffraction technique, afforded by intense synchrotron and laser plasma X-ray sources, now permits this structural information to be obtained over a range of time scales from nanoseconds to milliseconds and upwards following an excitation of the membrane system. This time-averaged and time-resolved structural information may provide considerable insight into structure-function relationships in biological membranes and, especially when combined with structural information on the membrane proteins involved at atomic resolution, may provide this insight at the atomic level.