The control by internal calcium of membrane permeability to sodium and potassium

1. A study has been made of the relationship between the concentration of internal calcium and the permeability of human red cell membranes to sodium and potassium.2. Fresh red cells contain very little calcium, but after being depleted of ATP by ageing they took up calcium from Ringer solution. The entry was unaffected by external sodium and potassium but was markedly pH dependent. When supplied with energy, calcium-loaded cells actively extruded calcium by a saturable process which was also unaffected by the distribution of sodium and potassium across the membranes. The activity of the calcium pump was sufficient to maintain the low internal concentration found under physiological conditions.3. Raising internal calcium in metabolically poor cells caused a loss of cell potassium which was greater than the concomitant sodium gain. These changes were reversed when ATP was supplied. External calcium had no effect. The increase in permeability to sodium and potassium was enhanced by the simultaneous addition of fluoride, and, even more so, of iodoacetate. These inhibitors had no effect on membrane permeability unless calcium was also present. Inosine potentiated the action of fluoride and iodoacetate in causing potassium loss, by allowing more calcium to enter the cells.4. The results suggest that the permeability of human red cell membranes to sodium and potassium is regulated by internal calcium, which in turn is controlled by a calcium pump that utilizes ATP.     

Automated estimation of sodium, potassium, and calcium using the Eppendorf flame photometer

An Eppendorf flame photometer may be used to estimate sodium, potassium, and calcium in plasma which has been automatically sampled and diluted. Readings may be automatically recorded by feeding the output from the photomultiplier into a sensitive recorder. This method estimates 60 samples an hour, using approximately 0.12 ml. plasma per estimation. The accuracy of the method is discussed.     

The magnesium, calcium, sodium, potassium and chloride contents of the term human placenta

The ion content of the human term placenta was determined. When ordered decreasingly according to their placental content, the series of ions was: Na greater than Cl greater than K greater than Ca greater than Mg. These levels, plotted as a function of the tissue dry weight, showed an exponential distribution. Using Cl as an extracellular marker, Na and K cellular concentrations were evaluated. The equilibrium potentials derived from these values were very different from the measured syncytial membrane potential or from the value usually recorded in non-innervated tissues.     

Determination of ionized serum calcium, potassium, and sodium levels in fresh and frozen samples from cats

In order to determine the influence of pH and storage (7 days at ?18 °C) on ionized calcium, potassium, and sodium measurement in feline serum, blood samples from 66 healthy adult cats were obtained based on aerobic method via jugular venipuncture. From each sample, the serum aliquot was divided into two samples: the first sample was processed 30 min after blood collection, and the second was frozen at ?18 °C and stored for 7 days before being processed. For each serum sample, ionized calcium, potassium, and sodium were measured together with the pH. Significant differences between fresh and frozen serum samples were found for ionized calcium concentration (the average values were 4.630?±?0.043 and 4.183?±?0.058 mg/dl, respectively) and pH (the average values were 7.352?±?0.007 and 7.519?±?0.010, respectively). Sodium and potassium serum concentration showed no significant difference between fresh and frozen serum samples. For all parameters, there was no significant difference between males and females between the fresh and frozen serum samples, and therefore, the results for both genders were analyzed together.     

Correlation between sodium and potassium excretion in 24- and 12-h urine samples

Low-sodium and high-potassium diets have been recommended as an adjunct to prevention and treatment of hypertension. Analysis of these nutrients in 24-h urine has been considered the reference method to estimate daily intake of these minerals. However, 24-h urine collection is difficult in epidemiological studies, since urine must be collected and stored in job environments. Therefore, strategies for shorter durations of urine collection at home have been proposed. We have previously reported that collecting urine during a 12-h period (overnight) is more feasible and that creatinine clearance correlated strongly with that detected in 24-h samples. In the present study, we collected urine for 24 h divided into two 12-h periods (from 7:00 am to 7:00 pm and from 7:00 pm to 7:00 am next day). A sample of 109 apparently healthy volunteers aged 30 to 74 years of both genders working in a University institution was investigated. Subjects with previous myocardial infarction, stroke, renal insufficiency, and pregnant women were not included. Significant (P < 0.001) Spearman correlation coefficients (r_s) were found between the total amount of sodium and potassium excreted in the urine collected at night and in the 24-h period (r_s = 0.76 and 0.74, respectively). Additionally, the 12-h sodium and potassium excretions (means ± SD, 95% confidence interval) corresponded to 47.3 ± 11.2%, 95%CI = 45.3-49.3, and 39.3 ± 4.6%, 95%CI = 37.3-41.3, respectively, of the 24-h excretion of these ions. Therefore, these findings support the assumption that 12-h urine collected at night can be used as a reliable tool to estimate 24-h intake/excretion of sodium and potassium.     

Voltage-dependent sodium and potassium,but no calcium conductances in DDT1 MF-2 smooth muscle cells

Voltage-dependent inward and outward membrane currents were investigated in the DDT₁ MF-2 smooth muscle cell line using the whole-cell patch-clamp technique. Application of a pulse protocol with subsequent depolarizing voltage steps elicited an inactivating inward current and a non-inactivating outward current. The outward current was activated at membrane potentials more positive than –35 mV, with _act=30–40 ms. The outward current was blocked by tetraethylammonium (NEt₄Cl) and 3, 4-aminopyridine in a dose-dependent manner (EC₅₀ of 5 mM and 0.5 mM, respectively). The amplitude of the outward current was linked to the potassium equilibrium potential (V_ek), and tail currents reversed near V_ek. The outward current was completely abolished when intracellular potassium was substituted by 106 mM caesium and 20 mM NEt₄Cl. The inward current was activated at potentials more positive than –30 mV with _act of 1.6–2.5 ms, and with _inact of 1.7–3.0 ms. Steady-state inactivation was 50% at a holding potential of –40 mV. The inward current was blocked by tetrodotoxin (EC₅₀ of 0.15 M) and dependent on the reversal potential for sodium. Voltage-dependent calcium currents could not be detected. Further, the cytoplasmic free calcium concentration, as measured using Indo-1 fluorescence, was not changed during high-potassium(40 mM)-induced depolarization. In contrast, contraction of freshly obtained hamster vas deferens tissue elicited by high-potassium(40 mM)-induced depolarization was largely inhibited by diltiazem (20 M). These findings showed that voltage-dependent calcium channels are not functional in DDT₁ MF-2 smooth muscle cells in contrast to freshly obtained Syrian hamster vas deferens smooth muscle. It is concluded that at least two populations of voltage-dependent channels are present in DDT₁ MF-2 smooth muscle cells, conducting a slow outward rectifying current carried by potassium, and a fast, inactivating sodium current.     

Distribution of sodium, magnesium, phosphorus, sulphur, chlorine, potassium, calcium and iodine in mammalian thyroid gland.

Anhydrous specimen preparation techniques and X-ray microanalysis were used to study the elemental composition of the rat thyroid follicular cells and colloid in the follicular lumen. Analysis were performed in morphologically defined follicular cells and adjacent colloid. Use of semithin cryosections allowed us to selectively analyze cell nucleus and dense vesicles in the cytoplasm of follicular cells. The analytical results indicate that the basolateral and apical cell membrane of follicular cells act differently in the transport of iodine and other ions, thus creating ionic gradient in the follicular lumen as compared to that found in the follicular cells. High potassium levels were found in the colloid. This finding indicates an active secretion of potassium from the apical plasma membrane into the follicular lumen. High sulphur and calcium levels were also found in the colloid. Dense vesicles found in the cytoplasm of follicular cells varied in size and had different elemental composition.     

Quality control slide for potassium hydroxide and cellufluor fungal preparations.

An opaque, water-insoluble quality control material with a skinlike microscopic appearance was prepared by inoculating melted xanthine (0.4%) agar with filamentous fungi and dispensing drops onto glass slides. After solidification of the agar, the material was rapidly cleared by 10% KOH, revealing fungal elements stained by Cellufluor reagent.     

G-CSF对豚鼠单个缺血心房肌细胞钙、钠、钾电流的影响

目的:采用膜片钳全细胞记录方法,观察粒细胞集落刺激因子(G-CSF)急性干预对分离的豚鼠单个缺血心房肌细胞钙、钠、钾电流的影响。方法:使用酶解方法获得豚鼠单个心房肌细胞,在缺血缺氧条件下,采用全细胞膜片钳技术观察记录不同浓度G-CSF急性干预对钙通道电流-电压曲线、激活曲线、失活曲线,钠通道电流-电压曲线、激活曲线、失活曲线、静态失活曲线,延迟整流钾通道及其快成分、慢成分电流-电压曲线的影响。结果:随G-CSF浓度的增加,缺血心房肌细胞膜L型钙通道电流较缺血对照组有明显增大。当G-CSF浓度超过100μg/kg后,L型钙通道电流的增强维持于同一水平。当给予G-CSF浓度为300μg/kg时最大激活电压发生改变,较前有所增加。激活曲线与失活曲线未见明显改变。不同浓度G-CSF对缺血心房肌细胞膜钠离子通道电流无明显影响。G-CSF干预缺血心房肌细胞膜延迟整流钾电流未见明显改变,但延迟整流钾电流快成分在G-CSF 100μg/kg干预后明显增加,而延迟整流钾电流慢成分未见明显改变。结论:G-CSF对于缺血心房肌细胞部分通道的作用影响基本为非电压依赖性,但具有浓度依赖性,可能减少缺血心房心律失常的发生率。