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PubMed1984

Influence of intravenous Mg++ solutions on renal excretion of potassium, sodium, calcium, chloride, intraleukocytic potassium and peripheral vascular resistance: a metabolic and hemodynamic study in normal volunteers.

In an open randomized crossover trial 8 healthy male volunteers received an intravenous infusion of potassium chloride, potassium/magnesium chloride, potassium-(D,L)-aspartate, and potassium/magnesium-(D,L)-aspartate. Equimolar amounts of potassium (27.75 mmol) and magnesium (13.9 mmol) were given in a 500-ml volume during 24 h. During two 9-day periods subjects were maintained on a constant diet with a daily intake of 80 mmol potassium and 60 mmol magnesium. Infusions were administered on day 5 and 7 of each period. Serum and urine electrolyte concentrations as well as intraleukocyte potassium were measured before, during, and after the tests; cardiac output and systemic vascular resistance were determined by impedance cardiography. Potassium and magnesium containing solutions did not influence renal elimination of potassium, and also the circadian rhythm of potassium excretion did not show any change. The elimination of sodium, calcium, potassium, and chloride rose significantly over the corresponding control values during magnesium infusions, but not when potassium salts were given. The increase of calcium excretion after Mg++ is most probably due to suppression of parathyroid hormone. Intraleukocyte potassium was not affected significantly by the various infusions, indicating that intracellular compartments are completely filled. There was no evidence that the anion (D,L-aspartate or chloride) had a significant effect on all measured variables. Mean arterial blood pressure and peripheral vascular resistance were not altered significantly during the infusions.

Adult↗
PubMedDate not supplied

A clinical comparison of potassium and magnesium-potassium crystalloid cardioplegia: metabolic considerations.

Controlled metabolic studies were used to gauge the relative efficacy of two cardioplegic solutions in 28 patients (14 in each group) undergoing multiple coronary artery bypass grafts. A solution containing magnesium-potassium (Plegisol) was compared to a standard potassium crystalloid cardioplegic solution. Measurements of coronary blood flow, coronary vascular resistance, coronary arteriovenous oxygen difference, myocardial oxygen consumption and extraction, and myocardial lactate and potassium extraction and release were all measured in the isolated, vented, paced, beating heart, before and for 15 minutes after a one hour arrest interval during which time revascularization was completed. During cardioplegic administration, the infusion flow rate, myocardial oxygen consumption and extraction, and lactate and potassium release and uptake were noted. The results indicate that during cardioplegic administration, the total oxygen consumed for both potassium and magnesium-potassium solutions did not significantly differ. The flow rate of the Mg-K solution was significantly higher than that of the potassium solution alone (510 vs. 398 ml/min). There was no lactate production during Mg-K administration, but 0.13 mEq/min of lactate was produced while potassium crystalloid cardioplegia was given. During myocardial reperfusion, oxygen extraction was maintained near prearrest levels in both groups. The only significant difference noted between the potassium and magnesium-potassium solutions were the higher coronary blood flow and oxygen consumption immediately upon reperfusion in the Mg-K group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

A comparison of the effects of central v peripheral bolus injections of potassium chloride on aortic root potassium concentrations in swine.

Clinically relevant doses of potassium chloride (equivalent to 2 mEq/60 kg of body weight) were administered as rapid intravenous (IV) boluses to healthy halothane-anesthetized pigs. Potassium was given either peripherally through a standard IV ear catheter or centrally through the central venous port of a pulmonary artery catheter. Multiple injections were made in each pig, and cardiac output was varied by changing end-tidal halothane concentration. The aortic root potassium concentration was measured every three to six seconds for 90 seconds following potassium administration in each pig. Monitored variables included end-tidal halothane, end-tidal carbon dioxide, pulmonary artery pressure, mean arterial blood pressure, cardiac output, electrocardiogram, and temperature. Following both peripheral and central administration of potassium chloride, aortic root potassium increased significantly. However, the time required to achieve the peak aortic root potassium concentration was significantly less after central administration. In addition, the change in aortic root potassium concentration was greater following central administration compared with peripheral. The change in aortic root potassium concentration correlated inversely with cardiac output only after central, but not peripheral injection. Despite marked transient hyperkalemia in all animals, no electrocardiographic evidence of hyperkalemia could be demonstrated. It is concluded that small bolus doses of potassium chloride (2 mEq/60 kg) can be given safely either peripherally or centrally in normal, hemodynamically stable swine.

Animals↗
PubMed1994

Role of ATP sensitive potassium channel in extracellular potassium accumulation and cardiac arrhythmias during myocardial ischaemia.

Extracellular potassium rises rapidly during myocardial ischaemia, correlating with the onset of ventricular arrhythmias. The extracellular accumulation of potassium can induce abnormalities in both impulse conduction and impulse generation. Inhomogeneities of potassium conductance will elicit regional differences in action potential duration and repolarisation. The resulting spatial dispersion of refractory period will allow for fragmentation of impulse conduction on ensuing beats, the formation of irregular reentrant pathways and ventricular fibrillation. In a similar manner, the spread of injury current from the ischaemic tissue to surrounding normal tissue can trigger extrasystoles (depolarisation induced automaticity). It has been hypothesised that the activation of the ATP sensitive potassium channel contributes significantly to reductions in action potential duration and increases in extracellular potassium accumulation during myocardial ischaemia. ATP sensitive potassium channel antagonists prevent ischaemically induced reductions in action potential duration and the dispersion of refractory period but may induce oscillatory afterpotentials under some conditions (for example, calcium overload). In contrast, potassium channel agonists enhance the dispersion of refractory period ischaemia, which promotes the formation of re-entrant arrhythmias. The pharmacological modulation of the ATP sensitive potassium channels could therefore offer a novel approach for the management of cardiac arrhythmias in patients with ischaemic heart disease. In general, channel antagonists prevent ventricular fibrillation, while high (hypotensive) doses of channel agonists can induce malignant arrhythmias during ischaemia in animal models. However, recent evidence also suggests that potassium channel agonists may promote a better preservation of myocardial mechanical performance during reperfusion while ATP sensitive potassium channel antagonists exacerbate mechanical depression during ischaemia in experimental models.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1989

Enhancement of potassium-sensitive current in heart cells by pinacidil. Evidence for modulation of the ATP-sensitive potassium channel.

Pinacidil belongs to a novel group of compounds that enhance the potassium permeability of vascular smooth muscle. Evidence also exists that this drug enhances the potassium permeability of cardiac tissue. The purpose of the present investigation was to determine if pinacidil alters potassium-channel activity in heart and, if so, which potassium channel is the target. We used the whole-cell arrangement of the patch voltage clamp to record membrane currents from isolated guinea pig ventricular cells. In solutions designed to isolate potassium currents, pinacidil enhances a time-independent current positive to the potassium equilibrium potential. Current measured at voltages negative to the potassium equilibrium potential are essentially unaltered by the drug. The potassium sensitivity of outward current indicates that the target for the drug is a potassium channel. Experiments designed to test for voltage-dependent channel gating strongly suggest that the pinacidil-sensitive current is not voltage gated. Pinacidil-sensitive current is blocked by externally applied Ba2+, Cs+, and tetraethylammonium ion. In addition, it is potently blocked after external application of 100 nM glibenclamide. Taken along with the time- and voltage-independent properties of pinacidil-sensitive current, this pharmacology strongly suggests that the target for pinacidil in heart is the ATP-sensitive potassium channel.

Adenosine Triphosphate↗
PubMed1981

Urine and serum potassium levels after potassium cardioplegia.

Potassium cardioplegia for myocardial preservation is being used extensively in heart operations. This study was designed to determine the effect of potassium cardioplegia on serum and urine potassium levels. A control group of 11 patients was compared to a study group of 24 patients. Myocardial preservation in the control group was achieved by whole body cooling to 20 degrees to 30 degrees C and in the study group, by repeated injections every 30 minutes of 500 to 700 ml of cold pump blood, containing potassium chloride 30 mEq/L, into the aortic root after aortic clamping. Total potassium dose in the study group was 46 +/- 21 mEq (mean +/- SD). Mean serum potassium level was significantly higher during and after bypass in the study group (after bypass: control 3.65 +/- 0.11 mEq/L, study 4.24 +/- 0.10 mEq/L [mean +/- SE], p less than 0.005), but was within normal limits in both groups. Urine potassium levels and excretion rates were significantly higher in the study group (potassium excretion rate after bypass: control 6.1 +/- 0.7 mEq/hr, study 11.3 +/- 0.9 mEq/hr [mean +/- SE], p less than 0.0025). We conclude that no special measures are required to facilitate potassium excretion when total potassium cardioplegia dose is not greater than 50 mEq.

Adult↗
PubMed1998

Effect of mineralocorticoid activity on transtubular potassium gradient, urinary [K]/[Na] ratio, and fractional excretion of potassium.

Clinical assessment of potassium derangements may require evaluation of mineralocorticoid status. Several indirect indices of mineralocorticoid activity based on renal electrolyte excretion have been proposed and include the transtubular potassium gradient, urinary [K]/[Na] ratio, and renal fractional excretion of potassium. We studied the impact of high mineralocorticoid activity versus blocked mineralocorticoid activity on these indices in otherwise normal subjects who ingested a defined diet. Eight normal subjects received either fludrocortisone or spironolactone for 4 days. After a washout period of > or = 2 weeks, each subject then received the opposite regimen. Subjects ingested an identical high-potassium diet during both experimental periods. The renal fractional excretion of potassium and transtubular potassium gradient were calculated using standard formulas. Fludrocortisone caused an increase in body weight and no significant reduction in serum potassium concentration, while spironolactone decreased body weight and increased plasma potassium concentration. After 1 or 2 days of treatment with fludrocortisone, the average values for all urinary indices of mineralocorticoid activity were significantly higher than after 1 or 2 days of treatment with spironolactone. However, the differences between these indices in the fludrocortisone and spironolactone test periods diminished by day 3 and were nonexistent by day 4. In conclusion, the transtubular potassium gradient, [K]/[Na] ratio, and renal fractional excretion of potassium reflect acute changes in mineralocorticoid activity. However, these indices do not discriminate between states of high and low mineralocorticoid activity lasting longer than 2 to 3 days.

Cross-Over Studies↗
PubMed2004

Does potassium concentration measured on blood gas analysis agree with serum potassium in patients with diabetic ketoacidosis?

OBJECTIVE: The aims of this study were to define the maximum clinically acceptable difference between potassium concentrations on different samples and to determine the degree of agreement between potassium concentration measured on blood gas analysis and serum for patients with diabetic ketoacidosis (DKA). METHODS: This project comprised two sub studies. In the first, 15 emergency physicians, intensivists and endocrinologists were surveyed and asked to mark on a line with markings at 0.5 mmol/L intervals, the maximum clinically acceptable differences (both above and below the 'true' value) between potassium concentration measured on different samples. The maximum clinically acceptable difference was calculated as the median of responses. The second study was a retrospective agreement study. Patients with an ED diagnosis of DKA were identified from a computer database. They were eligible for inclusion if they had both blood gas analysis including potassium concentration and serum potassium concentration and pH was less than 7.3. Data collected included potassium concentration on serum and blood gas samples, pH, serum glucose concentration and time of sample collections. Data were analysed using bias plot and Spearman correlation analyses. RESULTS: The maximum clinically acceptable difference was defined as 0.5 mmol/L for both over and underestimation of potassium concentration. Fifty patients were studied with a median pH of 7.17 and median serum glucose of 29.5 mmol/L. Difference in potassium concentration between samples ranged from -0.9-2.9 mmol/L. 80% of sample pairs had a difference within the maximum clinically acceptable difference defined previously. The magnitude of difference between samples correlated with serum glucose (P = 0.0033, coefficient 0.41) but not with pH. CONCLUSION: This study suggests that potassium concentration derived from blood gas analysis may not be an acceptable substitute for serum potassium concentration in patients with diabetic ketoacidosis, particularly at higher serum glucose concentrations.

Adult↗
PubMedDate not supplied

Muscle potassium content and potassium gluconate supplementation in normokalemic cats with naturally occurring chronic renal failure.

Muscle potassium content and supplementation with potassium gluconate were evaluated in normokalemic cats with chronic renal failure (CRF). Affected cats received standard medical therapy for renal failure and either placebo (sodium gluconate) or potassium gluconate. At the beginning of the study and after 6 months of supplementation, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were estimated using 3H-inulin and 14C-tetraethylammonium bromide (TEA) clearances. Muscle potassium content was determined in biopsy specimens using atomic absorption spectroscopy. Muscle biopsy samples obtained from cats with CRF before treatment had significantly lower muscle potassium content than did those from normal control cats. Over the 6-month period of supplementation, muscle potassium content increased both in cats with CRF that received potassium gluconate and in those that received placebo (sodium gluconate). Serum potassium concentration and fractional excretion of potassium remained relatively unchanged in both groups of cats throughout the treatment period. There were no significant differences in the percentage change in GFR and ERPF between treatment groups over the 6-month time period. Median values for pH, HCO3-, and total CO2 at 6 months were higher than baseline in the potassium gluconate group but lower than baseline in the sodium gluconate group.

Animals↗
PubMed1979

Whole body potassium and total exchangeable potassium in elderly patients with cardiac-failure.

Body potassium status of patients with cardiac failure may be estimated by a number of methods, but increasing reliance is being placed upon radioisotope dilution with 42K which measures the total exchangeable potassium. Total exchangeable potassium comprises between 86 per cent and 97 per cent of whole body potassium in healthy subjects. We have measured total exchangeable potassium in 22 oedema-free elderly patients with stable cardiac failure and compared the results with simultaneously determined measurements of whole body potassium obtained by whole body counting. The mean whole body potassium was 2360 +/- 640 mmol. The mean value of total exchangeable potassium measured at 24 hours was 1820 +/- 610 mmol (77% of whole body potassium) and increased further to 2000 +/- 600 mmol (84%) when measured after 48 hours. In patients with cardiac failure and, perhaps, also other patients with a history of fluid retention, the mixing of a tracer dose may be significantly delayed, which if not appreciated may lead to an overestimate of potassium depletion.

Aged↗
PubMed1976

Potassium secretion by colonic mucosal cells after potassium adaptation.

Recent studies have demonstrated that chronic potassium loading increases Na-K-ATPase specific activity in kidney tissue and suggest that this enzyme plays a role in renal potassium adaptation. Studies of fluid and electrolyte movement, potential difference (PD), AND Na-K-ATPase were performed in colon and jejunum of the rat in order to further characterize the relationship of Na-K-ATPase to potassium secretion. Experimental rats fed 2.6 meq K/gm diet for 7 days were compared to a control group fed 0.13 meq K/gm. In the colon, chronic potassium loading increased potassium secretion from 0.8 +/- 0.2 to 3.9 +/- 0.9 mueq/min per g tissue (P less than 0.01) and PD from 27 +/- 5.0 to 54 +/- 2.6 mV (P less than 0.001), lumen negative, as Na-K-ATPase increased from 5.0 +/- 0.5 to 11.4 +/- 1.0 muM Pi/mg protein per h (P less than 0.001). In contrast, there was no change in PD, potassium movement, or Na-K-ATPase in the jejunum of potassium-loaded rats. Colonic movement of water, sodium, and chloride was similar in the control and potassium-loaded rats. These results indicate that increased Na-K-ATPase is associated with both increased PD and increased potassium secretion in the colon and provide additional evidence suggesting that Na-K-ATPase may be important in the control of transepithelial potassium movement.

Action Potentials↗
PubMed1987

Plasma potassium and diurnal cyclic potassium excretion in the rat.

The relation of the plasma potassium concentration to the daily cyclic variation in potassium excretion was examined in undisturbed, unanesthetized male Sprague-Dawley rats maintained on a liquid diet in a 12-h light-dark environment. Potassium excretion increased from a light-phase minimum of 16 mu eq/h to a peak of 256 mu eq/h 3 h after the beginning of the dark phase. Plasma potassium concentration in arterial blood, sampled in rats at 90-min intervals during these changes in potassium excretion, showed no significant change and was in the range 4.50-4.99 meq/liter. In adrenalectomized rats receiving aldosterone and dexamethasone at constant basal rates by implanted pumps, the daily cycle of potassium excretion was the same as in the intact rats, and plasma potassium was not significantly different when measured at the time of minimum and maximum rates of potassium excretion (4.79 +/- 0.42 vs 5.16 +/- 0.47 meq/liter, mean +/- SD). These results indicate that plasma potassium concentration is not the efferent factor controlling diurnal cyclic changes in potassium excretion in adrenal intact rats and may not be the only significant factor in adrenalectomized-steroid replaced rats.

Adrenalectomy↗
PubMed1981

Relationship between plasma and cellular potassium content during potassium repletion.

The simultaneous effect of two weeks of potassium repletion therapy on the plasma concentration and total body content of potassium was assessed in seven patients with hypokalaemia. Glomerular filtration rate, renal plasma flow, and maximal urinary concentration were also measured both before and after therapy with potassium chloride. While the plasma potassium concentration quickly returned to normal, total body content of potassium remained depressed, emphasizing the unreliability of the plasma potassium concentration as an indicator of total body potassium status. Parameters of renal function measured in this study, which were depressed by potassium depletion, also did not alter with correction of the plasma potassium level. This suggests that these functions are primarily affected by cellular potassium content.

Aged↗
PubMed2006

[Root exudates of potassium-enrichment genotype grain amaranth and their activation on soil mineral potassium].

With solution culture experiment, this paper studied the effects of two potassium supply levels on the root exudates content and its dynamics of two grain amaranth genotypes (potassium-enrichment K12 and ordinary M9), and the activation of root exudates on soil mineral potassium. The results showed that the root exudation rates of soluble sugar, amino acids and organic acids of these two genotypes were decreased with increasing potassium supply level, which was higher in K12 than in M9. The root exudation capability of the two genotypes was similar under normal potassium supply level, while that of K12 was significant higher than M9 under low potassium supply level. Organic acid was the main root exudate under two potassium supply levels, which was several decuples or hundreds times as much as that of soluble sugar and amino acids. Compared with those at the fortieth day, the exudation rates of soluble sugar, amino acids and organic acids at the fiftieth day decreased rapidly in M9, while decreased slowly in K12. At three growth phases, the contents of soluble sugar, amino acid and organic acid were higher in the root exudate of K12 than in that of M9, and the difference of the two genotypes became significant with time extended. The content of organic acid in root exudate was accounted for >93% in the two genotypes at three growth phases. Soil available potassium content after treated by the root exudates of grain amaranth was higher than that treated by pure water. Under low potassium stress, the content of soil available potassium treated by the root exudates of K12 was higher than that treated by those of M9.

Amaranthus↗
PubMed1990

[Hyperkalemia with potassium-sparing and potassium-losing diuretics. Results from the Comprehensive Hospital Drug Monitoring Bern (CHDM)].

Of 5047 in-patients in the Division of Internal Medicine, Zieglerspital Bern (regional/teaching hospital), admitted from 1982 to 1985, 2412 were treated with at least one diuretic. The hospital records of these patients were reviewed with regard in particular to serum potassium and creatinine values as well as potassium supplementation. On the basis of this evaluation the patients were assigned to 6 different treatment groups and the relative occurrence rate of hyperkalemia probably related to drug treatment was determined. Of the 590 patients treated with only potassium losing diuretics, none was found to show a hyperkalemia event; of the 742 patients on potassium losing diuretics and potassium supplementation, 27 (3.6%) developed hyperkalemia. In the 439 patients under combined diuretics (potassium sparing with potassium losing) without potassium substitution, 76 (17.3%), and in the 381 under combined diuretics with potassium substitution 24 (6.3%), developed hyperkalemia. The further groups of patients are also described. Renal function was estimated by the formula of Cockcroft and Gault. Reduced renal function is a significant risk-factor for hyperkalemic events under combined diuretics. All hyperkalemic events were within a serum potassium range of 5.1-7.0 mmol/l.

Creatinine↗
PubMed1986

Influence of potassium depletion on potassium conductance in proximal tubules of frog kidney.

In order to test for the contribution of intracellular potassium activity to the link of sodium/potassium-ATPase activity and potassium conductance, studies with conventional and potassium selective microelectrodes were performed on proximal tubules of the isolated perfused frog kidney. The peritubular transference number for potassium (tk), i.e., the contribution of peritubular slope potassium conductance to the slope conductance of the cell membranes (luminal and peritubular), was estimated from the influence of peritubular potassium concentration on the potential difference across the peritubular cell membrane (PDpt). During control conditions, PDpt is -65 +/- 1 mV, intracellular potassium activity (Ki) 57 +/- 2 mmol/l and tk 0.41 +/- 0.05. The resistance in parallel of the luminal and peritubular cell membranes (Rm) is 44 +/- 4 k omega cm, the resistance of the cellular cable (Rc) 137 +/- 13 M omega/cm. When the cells are exposed 10 min to potassium free perfusates (series I), PDpt increases by -28 +/- 3 mV within 2 min and then decreases gradually to approach the control value within 10 min. Ki decreases by 22 +/- 3 mmol/l and Rc increases by 35 +/- 10%. After a transient decrease, Rm increases by 36 +/- 9%. Readdition of peritubular potassium leads to a transient increase of PDpt, a gradual decrease of Rm and Rc as well as a gradual increase of Ki. tk recovers only slowly to approach 65 +/- 8% of control value within 3 and 79 +/- 10% within 6 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Potassium supplements and total body potassium in elderly patients.

Total body potassium (TBK) and serum potassium measurements have been obtained in nine elderly patients in controlled heart failure on differing diuretic regimens. The patients were randomly maintained on a potassium-sparing diuretic, on frusemide, and on frusemide with potassium supplements (48 mmol/day) for a minimum of one month. TBK levels increased by a mean of 128 mmol on frusemide with potassium supplements compared with no supplements (P less than 0.001), a 7% increase in TBK. Serum potassium levels increased, similarly, from 4.1 mmol/l to 4.8 mmol/l (P less than 0.01). The potassium-sparing diuretic had the same effect as frusemide with supplements in increasing TBK in six patients. However, in three cases there was no increase in TBK compared with frusemide alone. The results demonstrate that potassium supplements are effective in raising TBK levels and serum potassium levels in elderly patients with heart failure.

Aged↗
PubMed1998

Effects of ATP-sensitive potassium channel opener on potassium transport and alveolar fluid clearance in the resected human lung.

Since the effect of an ATP-sensitive potassium channel (KATP channel) opener on the function of alveolar epithelial cells is unknown, the effect of YM934, a newly synthesized KATP channel opener, on potassium influx into the alveolar spaces and alveolar fluid clearance was determined in the resected human lung. An isosmolar albumin solution with a low potassium concentration was instilled into the distal airspaces of resected human lungs. Alveolar fluid clearance was measured by the progressive increase in alveolar protein concentration. Net potassium transport was measured by the change in potassium concentration and alveolar fluid volume. YM934 (10(-4) M) increased net influx of potassium by 140% into the alveolar spaces and also increased alveolar fluid clearance by 60% in the experiments with a potassium concentration of 0.3 mEq/1. Glibenclamide (10(-4) M), a KATP channel blocker, inhibited the YM934-increased influx of potassium transport and the increase in alveolar fluid clearance. Also amiloride (10(-5) M), an inhibitors of apical sodium uptake, blocked the YM934 stimulated increase in net alveolar fluid clearance. These results indicate that a KATP channel opener can effect potassium transport and net vectorial fluid movement across the human alveolar epithelium.

Adenosine Triphosphate↗