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At least 217 records · Page 12Linked to original sources
PubMed1984

Potassium channel kinetics in squid axons with elevated levels of external potassium concentration.

Potassium ion current in squid axons is usually modified by the effects of ion accumulation in the periaxonal space during voltage-clamp depolarization. The time course of potassium channel activation and ion accumulation usually overlap. A widely accepted procedure for circumventing the effects of accumulation in measurements of activation kinetics consists of measuring the difference in the current at the end of a depolarizing pulse and immediately following return of the membrane potential to the holding level. This instantaneous jump procedure is based upon the assumptions that the potassium channel current-voltage relation (IV) is a linear function of the driving force, and that the IV and the potassium channel-gating kinetics are both independent of ion accumulation. The latter assumption appears to be appropriate for activation kinetics. However, both assumptions concerning the IV are incorrect, in general. Consequently, the jump procedure provides a misleading view of gating kinetics for membrane depolarizations that produce net current flow. Jump conductance measurements for depolarizations that produce little or no net current indicate that the Hodgkin-Huxley n4 model of potassium channel kinetics is appropriate for the physiological range of membrane potentials.

Animals↗
PubMed2000

Loss of total body potassium during rapid weight loss does not depend on the decrease of potassium concentration in muscles. Different methods to evaluate body composition during a low energy diet.

OBJECTIVE: The aim of the study was to elucidate whether combustion of skeletal muscle glycogen during a very low calorie diet (VLCD) was associated with decreased muscle potassium content. A comparison between different methods was also performed to evaluate body composition during a VLCD and a low calorie diet (LCD). DESIGN: Dietary treatment of obese women by VLCD and LCD. Measurements after 1 and 2 weeks of VLCD and 6 months of LCD. SUBJECTS: Fifteen perimenopausal obese women aged 46.5+/-1.3 y and 15 of 48.0+/-0.7 y of age. MEASUREMENTS: Skeletal muscle biopsies under local anaesthesia. Body composition measurements by means of deal-energy X-ray absorptiometry (DEXA), and measurements of total body potassium (40K) and total body nitrogen (TBN). Measurements of electrolytes and glycogen concentration in muscle samples. RESULTS: In the first study (1 week of VLCD) skeletal muscle glycogen decreased (P<0.01), but muscle potassium increased (P<0.01). Muscle sodium decreased (P<0.01), while muscle magnesium was unaltered. Body weight decreased by 2.9+/-0.5 kg and 40K decreased. Fat-free mass (FFM) calculated from 40K and DEXA decreased by 2.7 vs 1.9 kg (P<0.001). Body fat measured with DEXA decreased by 1.1 kg (P<0.01), but not body fat calculated from 40K. TBN decreased by 0.03+/-0.01 kg (P<0.05) and FFM calculated from TBN by 2.9+/-0.5 kg (P<0.002). In the second study, 6 months on the LCD resulted in 17.0+/-2.0 kg weight reduction and this was mainly due to reduced body fat, 14. 0+/-2.0 kg measured with DEXA and from 40K (P<0.001). The decrease in FFM was slight. CONCLUSION: One week of VLCD resulted in muscle glycogen depletion but increased muscle potassium content in spite of decreased total body potassium. FFM contributed to the main part of body weight loss during short periods of severe energy restriction, but remained unchanged during long-term dietary treatment. Body fat became mostly responsible for the body weight loss during long-term LCD. Calculations of changes of FFM from 40K and TBN seem to overestimate the FFM decrease associated with short-term VLCD. International Journal of Obesity (2000)24, 101-107

Absorptiometry, Photon↗
PubMed2001

Low-potassium and glucose-free dialysis maintains urea but enhances potassium removal.

BACKGROUND: The influence of potassium (K) removal on dialysis efficiency as measured by urea elimination is not clear. In this prospective, randomized, cross-over study we investigated the magnitude of K removal and its effect on urea (u) elimination during high-flux haemodialysis (HD). METHODS: Twelve stable, non-diabetic HD patients were investigated during three one-week standardized HD periods (1.8 m(2) high-flux polysulphone dialyser, treatment time 240 min, Qb = 300 ml/min, Qd = 500 ml/min, dialysate without glucose, bicarbonate 40 mmol/l), using dialysates containing 0 (0K), 1 (1K), and 2 (2K) mmol/l of K. Mass removal of K (M(K)) and u (M(U)) were measured during the mid-week treatment by partial dialysate collection. Urea reduction rate (URR) and Kt/V were determined. RESULTS: 0K, 1K and 2K treatments were perfectly comparable. Plasma K (PK) continuously declined reaching stable concentrations after 180 min. While 0K dialysate removed 117.1 mmol, 80.2 and 63.3 mmol (P < 0.001) were removed by 1K and 2K baths respectively. M(U) was not influenced by M(K) (r = 0.22) and amounted to 491.1 (0K), 508.6 (1K), and 506.2 (2K) mmol (NS) respectively. Accordingly, urea clearance, URR and Kt/V were constant during 0K, 1K and 2K treatments. CONCLUSIONS: Potassium-free dialysate significantly enhances potassium elimination. Potassium removal has no influence on urea elimination. High potassium removal, when needed, does not impair dialysis efficiency as measured by urea kinetics in high-flux, glucose-free, 40 mmol/l bicarbonate HD.

Adult↗
PubMed1982

Early changes in plasma potassium after acute alterations in PaCO2 in anesthetized dogs, monitored continuously with intravascular potassium-selective electrodes.

Changes in plasma potassium in the first 10 min after alterations in PaCO2 in anesthetized greyhounds were monitored continuously in vivo with potassium-selective electrode catheters. Elevation of PaCO2 resulted in a small transient fall in plasma potassium whereas reduction in PaCO2 resulted in a small transient rise in plasma potassium. Maximum changes occurred at approximately 5 min after alterations in PaCO2 with levels tending to return to control thereafter. Changes of similar magnitude in normal man would not be expected to have an adverse effect on cardiac function, but they may have greater significance in subjects with pre-existing abnormal potassium levels, during concurrent treatment with digoxin, and after sudden alterations in PaCO2 in chronic hypo- or hypercapnic conditions.

Animals↗
PubMed1992

Lack of effect of potassium channel openers on ATP-modulated potassium channels recorded from rat ventromedial hypothalamic neurones.

1. Single neuronal cells were freshly isolated from the ventromedial hypothalamic nuclei (VMHN) of the rat brain. Currents through ATP-modulated and large conductance (160 and 250 pS) calcium-activated potassium channels were recorded by the cell-attached and excised inside-out patch techniques. 2. BRL38227 (lemakalim; 30-90 microM) applied to the superfusing medium produced no change in firing rate of isolated glucose-receptive VMHN neurones in cell-attached recordings. 3. BRL38227, at concentrations of between 30-100 microM applied to the intracellular (cytoplasmic) aspect of inside-out patches, had no effect on the activity of ATP-sensitive K+ channels in the absence of ATP or in the presence of a sub-maximal inhibitory concentration (3 mM) of ATP. Cromakalim, pinacidil, minoxidil sulphate and diazoxide also produced no effect under these conditions. 4. The potassium channel openers (KCO's) were tested on ATP-activated potassium channels recorded from a further subpopulation of VMHN neurones. Application of BRL38227 (up to and including 100 microM) to this channel in inside-out patches either in the absence of ATP or when activated by 5 mM ATP had no effect on channel activity. Identical results were obtained with cromakalim and pinacidil. 5. BRL38227 had no effect on either of the large conductance (250 pS and 160 pS) calcium-activated potassium channels in VMHN neurones. 6. Intracellular recordings were made from glucose-receptive VMHN neurones in rat brain slices. Cromakalim (50 microM) or diazoxide (60 microM) did not alter the firing rate or passive membrane properties of these neurones demonstrated to be sensitive to tolbutamide (0.1 mM). 7. These results show that the KCO's tested in this study have no effect either on VMHN neurones contained in brain slices or on the activity of any of the ATP-modulated potassium channels under isolated patch conditions associated with these neurones.

Adenosine Triphosphate↗
PubMed1984

Potassium concentration in equine red blood cells: normal values and correlation with potassium levels in plasma.

The concentration of potassium in plasma and in red blood cells was determined in 948 horses. The coefficient of correlation between the two parameters was low. In 436 of these horses, which were clinically healthy, the red blood cell potassium (RBCK+) levels did not fit within a normal distribution curve, but a bimodal distribution was observed with a section point at 90 mmol/litre. In 90 per cent of these normal horses, mean RBCK+ content was 97.5 mmol/litre. In the remaining 10 per cent, mean RBCK+ concentration was 93.8 mmol/litre. A subdivision into a 'low potassium group' and a 'high potassium group' was made. In 10 out of 15 horses in the 'low potassium group', bimonthly sampling over a period of one year showed that RBCK+ content remained low. In the remaining five horses an increase was observed.

Animals↗
PubMed1996

Body composition derived from whole body counting of potassium in growth hormone-deficient adults: a possible low intracellular potassium concentration.

The validity of total body potassium (TBK) measurement in estimating fat mass and fat-free mass (FFM) in GHD adults was assessed by comparison with the reference technique of dual energy x-ray absorptiometry (DEXA). The TBK and FFM values determined by DEXA were used to calculate the potassium concentration per kg FFM in GH-deficient (GHD) adults and compared with standard values for normal subjects of 59.6 mmol for females and 66.4 mmol for males. There were considerable differences between predicted and measured TBK values for both males (3972 vs. 3577 mmol; P < 0.001) and females (2526 vs. 2277 mmol; P < 0.001). Similarly, the estimation of FFM and fat mass by TBK measurement was significantly inaccurate for both sexes compared to values determined by DEXA. These discrepancies may be accounted for by the lower calculated potassium concentrations compared with standard values for both males (56.2 vs. 66.4 mmol; P < 0.001) and females (53.1 vs. 59.6 mmol; P < 0.001). These observations suggest that caution should be exercised in the interpretation of TBK in GHD adults, and the reduced potassium concentrations would alleviate inaccuracies in the estimation of body composition. Secondly, the decreased intracellular potassium concentration of GHD adults may account for the decreased muscle strength and ease of fatigueability seen in GHD adults.

Absorptiometry, Photon↗
PubMed1987

Magnesium and potassium status in healthy subjects as assessed by analysis of magnesium and potassium in skeletal muscle biopsies and magnesium in mononuclear cells.

Magnesium and potassium concentrations were determined in plasma, erythrocytes and urine collected during 24 h, and in percutaneous muscle biopsies obtained in 30 healthy subjects. Magnesium was also analyzed in mononuclear cells. Men, compared to women, showed a higher urinary excretion of magnesium (p less than 0.05). The magnesium contents in mononuclear cells correlated significantly with the concentrations of magnesium in muscle biopsies (r = 0.63; p less than 0.001) and with the urinary losses of magnesium (r = 0.40; p less than 0.05). A significant interrelationship between magnesium and potassium was found in striated muscle (r = 0.65; p less than 0.001), and the contents of potassium in muscle biopsies correlated significantly with the levels of potassium in plasma (r = 0.41; p less than 0.05). In a separate study the day-to-day variations for the magnesium and potassium parameters were investigated during 5 consecutive days in 7 healthy subjects. The coefficient of variation for magnesium in mononuclear cells was comparably low (8.0%), considering the wide range between the subjects. This indicates that magnesium in mononuclear cells might be a valuable parameter in longitudinal follow-up studies.

Adult↗
PubMed1979

Potassium-induced cardioplegia during normothermic cardiac arrest. Morphologic study of the effect of varying concentrations of potassium on myocardial anoxic injury.

Most corrective procedures as well as myocardial revascularization require a period of cardiac arrest, and numerous methods have been proposed to protect the myocardium during this ischemic episode. Potassium-induced cardioplegia is one method that appears to be of benefit in this setting. Since it is recognized that myocardial necrosis may result at very high doses of potassium, we examined the effect of varying concentrations of potassium on myocardial anoxic injury. Using an isolated rat heart preparation, we evaluated anoxic injury occurring with cardioplegic solutions containing various concentrations of K+, ranging from 15 to 200 mEq. per liter, during a 50 minute normothermic arrest followed by 60 minutes of reperfusion. The transverse histologic sections of the left ventricular myocardium were analyzed for contraction band injury by morphometric and qualitative methods. Among the 62 animals studied the least severe anoxic injury was seen with K+ cardioplegia at concentrations of 25 and 30 mEq. per liter. At lower and higher concentrations there was little difference between the hearts exposed to anoxia with or without K+ cardioplegia. Potassium administered in very high doses, i.e., 100 or 200 mEq. of K+ per liter, led to contracture and extensive myocardial cell injury. This study suggests that potassium-induced cardioplegia is effective in reducing cell injury due to anoxia, and in this model an optimal concentration range was 25 to 30 mEq. per liter.

Animals↗
PubMed1999

Functional consequences of a decreased potassium affinity in a potassium channel pore. Ion interactions and C-type inactivation.

Ions bound near the external mouth of the potassium channel pore impede the C-type inactivation conformational change (Lopez-Barneo, J., T. Hoshi, S. Heinemann, and R. Aldrich. 1993. Receptors Channels. 1:61- 71; Baukrowitz, T., and G. Yellen. 1995. Neuron. 15:951-960). In this study, we present evidence that the occupancy of the C-type inactivation modulatory site by permeant ions is not solely dependent on its intrinsic affinity, but is also a function of the relative affinities of the neighboring sites in the potassium channel pore. The A463C mutation in the S6 region of Shaker decreases the affinity of an internal ion binding site in the pore (Ogielska, E.M., and R.W. Aldrich, 1998). However, we have found that this mutation also decreases the C-type inactivation rate of the channel. Our studies indicate that the C-type inactivation effects observed with substitutions at position A463 most likely result from changes in the pore occupancy of the channel, rather than a change in the C-type inactivation conformational change. We have found that a decrease in the potassium affinity of the internal ion binding site in the pore results in lowered (electrostatic) interactions among ions in the pore and as a result prolongs the time an ion remains bound at the external C-type inactivation site. We also present evidence that the C-type inactivation constriction is quite local and does not involve a general collapse of the selectivity filter. Our data indicate that in A463C potassium can bind within the selectivity filter without interfering with the process of C-type inactivation.

Alanine↗
PubMed1997

[Role of aldosterone in potassium secretion in chronic renal failure associated with hypertension (transtubular potassium gradient)].

Aldosterone protects against hyperkalemia in disorders with reduced number of over-working nephrons. It is not clear however, whether diminished aldosterone production or aldosterone resistance is responsible for the hyperkalemia in chronic renal failure. The importance of this question is underlined by the fact that antihypertensive drugs often reduce aldosterone level. Therefore we investigated the distal tubular potassium "driving force" (transtubular potassium gradient) in 9 patients with chronic renal failure accompanied by hypertension and compared it to the results obtained in 10 healthy persons. Glomerular filtration rate was 15.77 +/- 4.88 ml/min in the chronic renal patients. Serum potassium was normal in 3 of 9 patients, the average 4.88 +/- 0.16 mmol/l, higher than in healthy persons 4.27 +/- 0.09 mmol/l (p < 0.001). Nevertheless the transtubular potassium gradient was lower in patients (3.52 +/- 0.32) comparing to healthy persons (7.25 +/- 0.57, p < 0.001). The patients' plasma aldosterone was much higher than normal. The reduced tubular potassium secretion-decreased "driving force" --suggested to aldosterone resistance. We conclude that the renal tubules' aldosterone resistance is not an exceptional but rather frequent feature in chronic renal failure which should be considered when administering antihypertensive drugs.

Aldosterone↗
PubMed2001

Potassium and sodium ions in a potassium channel studied by molecular dynamics simulations.

We have performed simulations of both a single potassium ion and a single sodium ion within the pore of the bacterial potassium channel KcsA. For both ions there is a dehydration energy barrier at the cytoplasmic mouth suggesting that the crystal structure is a closed conformation of the channel. There is a potential energy barrier for a sodium ion in the selectivity filter that is not seen for potassium. Radial distribution functions for both ions with the carbonyl oxygens of the selectivity filter indicate that sodium may interact more tightly with the filter than does potassium. This suggests that the key to the ion selectivity of KcsA is the greater dehydration energy of Na(+) ions, and helps to explain the block of KcsA by internal Na(+) ions.

Bacterial Proteins↗
PubMed2001

Differential elution of sodium or potassium dihydrogen- and hydrogenphosphate ions from a sephadex G-15 column with sodium or potassium chloride solution.

When a mixed solution of sodium or potassium dihydrogenphosphate and disodium or dipotassium hydrogenphosphate was eluted from a Sephadex G-15 column with either a sodium or potassium chloride solution, the elution profiles of ions showed that the hydrogenphosphate ion was eluted more rapidly than the dihydrogenphosphate ion. When the sample solutions containing potassium dihydrogenphosphate and/or dipotassium hydrogenphosphate, all of which were supplemented with phosphorus-32-labelled potassium dihydrogenphosphate, were eluted with sodium chloride solution, the elution profiles of radioactivity showed that the dihydrogenphosphate ion changed to hydrogenphosphate ion and vice versa, depending on the pH values of the sample solution and the availability of the cation of the eluent during elution for the phosphate ion to pair with.

Chromatography, Ion Exchange↗
PubMed2000

Genomic organization and chromosomal localization of the murine 2 P domain potassium channel gene Kcnk8: conservation of gene structure in 2 P domain potassium channels.

A 2 P domain potassium channel expressed in eye, lung, and stomach, Kcnk8, has recently been identified. To initiate further biochemical and genetic studies of this channel, we assembled the murine Kcnk8 cDNA sequence, characterized the genomic structure of the Kcnk8 gene, determined its chromosomal localization, and analyzed its activity in a Xenopus laevis oocyte expression system. The composite cDNA has an open reading frame of 1029 bp and encodes a protein of 343 amino acids with a predicted molecular mass of 36 kDa. Structure analyses predict 2 P domains and four potential transmembrane helices with a potential single EF-hand motif and four potential SH3-binding motifs in the COOH-terminus. Cloning of the Kcnk8 chromosomal gene revealed that it is composed of three exons distributed over 4 kb of genomic DNA. Genome database searching revealed that one of the intron/exon boundaries identified in Kcnk8 is present in other mammalian 2 P domain potassium channels genes and many C. elegans 2P domain potassium channel genes, revealing evolutionary conservation of gene structure. Using fluorescence in situ hybridization, the murine Kcnk8 gene was mapped to chromosome 19, 2B, the locus of the murine dancer phenotype, and syntenic to 11q11-11q13, the location of the human homologue. No significant currents were generated in a Xenopus laevis oocyte expression system using the composite Kcnk8 cDNA sequence, suggesting, like many potassium channels, additional channel subunits, modulator substances, or cellular chaperones are required for channel function.

Amino Acid Sequence↗
PubMed1977

The effect of potassium supplements on total-body-potassium levels in the elderly.

Weight, skinfold thickness, grip strength and the total-body-potassium content were measured in 13 healthy elderly subjects before and after a three-month course of potassium supplements given in a dose of 36 mmol per day. There were no significant changes in the total-body-potassium content or in the ratio of total body potassium to lean-body mass. An increase in the right-hand grip strength may well have been a placebo effect.

Aged↗
PubMed2005

Plant responses to potassium deficiencies: a role for potassium transport proteins.

The availability of potassium to the plant is highly variable, due to complex soil dynamics, which are strongly influenced by root-soil interactions. A low plant potassium status triggers expression of high affinity K+ transporters, up-regulates some K+ channels, and activates signalling cascades, some of which are similar to those involved in wounding and other stress responses. The molecules that signal low K+ status in plants include reactive oxygen species and phytohormones, such as auxin, ethylene and jasmonic acid. Apart from up-regulation of transport proteins and adjustment of metabolic processes, potassium deprivation triggers developmental responses in roots. All these acclimation strategies enable plants to survive and compete for nutrients in a dynamic environment with a variable availability of potassium.

Acclimatization↗
PubMed1991

Effect of whole-body potassium depletion on plasma, erythrocyte, and middle gluteal muscle potassium concentration of healthy, adult horses.

The effects of whole-body potassium depletion induced by food deprivation on plasma, erythrocyte, and middle gluteal muscle K concentrations was quantified in 16 healthy, adult horses before, during, and at the end of a 7-day period of food deprivation during which water and sodium chloride were available ad libitum. Potassium concentrations were determined by atomic absorption spectroscopy. Plasma K concentration remained constant (3.49 +/- 0.09 mM K/L of plasma; mean +/- SEM) throughout the study. Erythrocyte potassium concentration decreased from 93.10 +/- 1.94 mM K/L of erythrocytes on day 0 to 88.63 +/- 2.39 mM K/L of erythrocytes on day 2 (decrease of 4.8%; P less than 0.05) and thereafter did not change. The K concentration of the middle gluteal muscle decreased from 91.06 +/- 2.96 microM K/g of muscle (wet weight) to 79.61 +/- 2.09 microM K/g of muscle (decrease of 12.6%; P less than 0.05) on day 4 and decreased further on day 7 to 73.62 +/- 1.85 microM K/g of muscle (decrease of 19.2%; P less than 0.05). There was no correlation between the plasma and erythrocyte K concentrations (r = -0.066), the erythrocyte and middle gluteal muscle K concentrations (r = 0.167), or the plasma and middle gluteal muscle potassium concentrations (r = -0.018). The water content of the middle gluteal muscle remained constant (73.23 +/- 0.36%) throughout the study. Erythrocyte membrane potential did not change (-99.26 +/- 0.87 mV) during the study, whereas the magnitude of the membrane potential of the middle gluteal muscle decreased from -105.84 +/- 1.67 mV on day 0 to -100.93 +/- 2.10 mV on day 7 (P less than 0.05).

Animals↗
PubMed1988

[Changes in the content of potassium, sodium and potassium influx in human peripheral blood lymphocytes during long-term cultivation with phytohemagglutinin].

Intracellular potassium, sodium and potassium influx were examined in PHA-activated human lymphocytes within 6 days of cultivation. DNA flow cytometry was used to estimate the percentage of cells in G1, S and G2 + M phases. Potassium influx and content per g protein were found to be increased, whereas sodium content decreased with the progression of cells from G1 to S phases, being maximum on the 3rd day. Later on the percentage of cells in S phase was seen diminished, and the potassium content decreased just as sodium content increased. It is concluded that ionic changes may correlate with the entering of cells into S phase.

Cell Cycle↗