CAT HEART MUSCLE IN VITRO. VI. POTASSIUM EXCHANGE IN PAPILLARY MUSCLES

The exchange of cell K with K⁴², J_K, has been measured in cat right ventricular papillary muscle under conditions of a steady state with respect to intracellular K concentration. Within the limits of the measurement, all of cell K exchanged at a single rate. Cells from small cats are smaller and have larger surface/volume ratios than cells from large cats. The larger surface/volume ratio results in larger flux values. J_K increases in an approximately linear manner as the external K concentration is increased twentyfold, from 2.5 to 50 mM, at constant intracellular K concentration. The permeability for K ions, P_K, calculated from the influx and membrane potential, remains very nearly constant over this range of external K concentrations. J_K is not affected by replacement of O₂ by N₂, or by stimulated contractions at 60 per minute, but K influx decreases markedly in 10^-5M and 10^-8M ouabain.

The monensin-mediated transport of Na+ and K+ through phospholipid bilayers studied by 23Na- and 39K-NMR

Addition of monesin to preparations of large unilamellar vesicles made from egg yolk phosphatidylcholine (EPC) in sodium or potassium chloride solution and from dioleoylphosphatidylcholine (DOPC) in sodium chloride solutions gives rise to dynamic 23Na- and 39K-NMR spectra. The dynamic spectra arise from the monensin-mediated transport of the metal ions through the membrane. The kinetics of the transport are followed as a function of monensin and metal ion concentrations and are compatible with a model in which one monensin molecule transports one metal ion. Rate constants for the association and dissociation of the monensin-metal complex in the membrane/water interface are extracted and the stability constants for complex formation are evaluated. The rate constants in DOPC are similar to those in EPC, confirming that diffusion is not rate-limiting in the transport process and that dissociation of the complex is the rate-limiting step. Although potassium on its own is transported more rapidly, sodium forms the more stable complex and is therefore transported preferentially in competition with potassium.

Potassium changes in megaloblastic anaemia

1. Serial measurements of serum potasssium and total-body potassium were made on eighteen patients with megaloblastic anaemia before the start of therapy and during the period of recovery. 2. In those patients who presented with an initial packed cell volume of less than 25%, a mean decrease in serum potassium of 0.4 mmol/1 occurred on average with 2.5 days of the start of therapy. This was followed by a significant increase in serum potassium during the period of recovery. There was a significant increase in total-body potassium in these patients, but this could be explained by increases in erythrocyte mass, erythrocyte potassium concentration and lean body mass.

Magnesium effects in rabbit ventricle

Ten to twenty millimoles per liter Mg did not affect 42-K exchange in control isolated blood-perfused rabbit septa, but abolished acetyl strophanthidin (ACS)-induced net 42-K loss (constant heart rate) without attenuating the mechanical response. In six septa ACS-induced net K loss was reduced from 159.3 plus or minus 45 to 43.5 plus or minus 35 mumol/kg tissue water (P smaller than 0.05) by increasing Mg from 1.0 to 20 mM without a change in inotropic response. Ten to twenty millimoles per liter Mg did not reverse ACS inhibition of 42-K5 tissue uptake. In eight septa 16 mM K doubled the efflux rate for 42-K in 1mM Mg. Twenty millimoles per liter Mg abolished this effect. Sixteen millimoles per liter K increase 42-K effluent counts by 99.5 plus or minus 18.5 percent of control in 1.0 mM Mg, but by 44.9 plus or minus 14.1 percent (P smaller than 0.001) in 20 mM Mg. Mg inhibited 42-K exchange at sites that became rate limiting after ACS treatment. These sites were activated by 16mM K. ACS inotrophy was not quantitatively related to net K loss. The Mg effect during digitalis exposure did not result from reversal of ACS inhibition of NA-K-ATPase activity but from a separate effect on K efflux.

Thallium-201 for myocardial imaging. Relation of thallium-201 to regional myocardial perfusion

Following intravenous administration, the myocardial concentration of tracer thallium-201, potassium-43, and rubidium-81 were determined in mice; thallium was present in the greatest concentration in the myocardium (2.08% compared 1.25% for potassium and 1.15% for rubidium at 10 minutes). The regional myocardial distribution of thallium-201 was determined in dogs under conditions of normal flow, and total occlusion, and compared with potassium-43 (r=0.97). The regional distribution of thallium-201 was compared to microspheres under conditions of partial occlusion and reactive hyperemia (r=0.97). Thallium-201 was evaluated in a series of phantom scans, which demonstrated that the low energy X-ray of thallium was suitable for imaging. These results suggest that thallium-201 can be used for the evaluation of the distribution of regional myocardial perfusion.

Distribution of sodium and potassium in chronic obstructive pulmonary disease

The body electrolyte composition of 34 patients with severe chronic obstructive pulmonary disease and without complications or medications known to influence body sodium or potassium was studied. Exchangeable sodium, exchangeable potassium, extracellular water, and total body water were measured using radioisotope dilution techniques. From these values and serum sodium and potassium levels, the intracellular water, intracellular concentrations of sodium and potassium, and factors to estimate lean body mass were calculated. Normal values were predicted for factors that vary with weight, age, and sex--exchangeable sodium, exchangeable potassium, total body water, extracellular water, intracellular water, and estimates of lean body mass--for each subject using regression equations that took into account the variables. For values that do not vary with weight or age--residual sodium and intracellular concentration of potassium--comparisons were made with values from our control subjects. The patients with chronic obstructive pulmonary disease showed a slower rate of potassium exchange than the control subjects, requiring at least 48 hours. There was also an increase in residual sodium composed of intracellular sodium and exchangeable bone sodium. The possibilities that the abnormalities could be ascribed to congestive heart failure, loss of lean tissue, or to a slowly functioning sodium pump were considered.

Thallium-201 for medical use. I

Thallium-201 merits evaluation for myocardial visualization, kidney studies, and tumor diagnosis because of its physical and biologic properties. A method is described for preparation of this radiopharmaceutical for human use. A critical evaluation of 201Tl and other radiopharmaceuticals for myocardial visualization is given.

Radionuclides and the patient with coronary artery disease

The emergence in the past 20 years of nuclear medicine as a distinct diagnostic discipline has been a major clinical advance. The relatively rapid evolution from the small laboratory limited primarily to the study of thyroid disease to the large unit in which radioactive tracers (radionuclides) are utilized to evaluate structure and function of most organ systems has been accelerated by major advances in instrumentation, new radioactive tracers and application of computer techniques. Application of these radionuclide techniques to the study of coronary artery disease has been quite recent, and has in part been limited by the need for a coordinated effort between the cardiologist and the specialist in nuclear medicine. However, realization of the potential usefulness of these techniques has fostered an increasingly productive liaison between the two specialties. The potential advantages of these radionuclides in evaluating patients with cardiovascular disease is twofold: first, they may permit the noninvasive or atraumatic acquisition of data that might otherwise be obtained only at the time of cardiac catheterization; second, and perhaps more important, they may permit the acquisition of physiologic measurements or observations not attainable by more conventional modes of study. Functionally, these techniques can be divided into those that evaluate cardiac performance and those that evaluate coronary blood flow, regional myocardial perfusion and myocardial viability.

The interaction of ATP-analogues possessing a blocked gamma-phosphate group with the sodium pump in human red cells

1. The (Na++K+)-ATPase of red cell membranes is unable to hydrolyse ATP-analogues in which the oxygen atom linking the beta- and gamma-phosphate groups is replaced by a minusCH2minus or minusNH-bridge. 2. In resealed ghosts both these ATP-analogues support K:K exchange but not Na:K exchange. ATP supports both modes of operation of the sodium pump, whereas neither occurs without any nucleotide. 3. These results support the hypothesis that ATP is needed as a cofactor for K:K exchange to occur, and make it extremely unlikely that phosphorylation from ATP is involved.

Kinetics of Na+-dependent K+ ion transport in a marine pseudomonad

The effect of external Na plus concentration on the transport of K plus was studied using K plus-depleted cells of a marine pseudomonad. K plus transport was found to be a saturable process and requires Na plus. The initial rates for K plus transport over a range of external K plus concentrations were measured in suspensions containing various fixed concentrations of Na plus. Reciprocals of the initial rates for K plus transport were plotted against reciprocals of the external concentration of K plus or Na plus to yield two primary Lineweaver-Burk plots. The experimental data were found to fit bisubstrate enzyme kinetics, with a sequential type mechanism. However, the initial rate data did not allow distinction between ordered or random mechanisms. The results suggest that Na plus and K plus form a ternary complex with a specific K plus carrier molecule on the outer surface of the membrane prior to translocation and the release of K plus inside the cell.

Studies on whole-body potassium in non-ketoacidotic diabetics before and after treatment

Serial measurements of whole-body potassium were carried out in 28 diabetic patients, in 23 of whom diabetes had only recently been diagnosed. Eleven patients were treated with insulin, 12 with oral hypoglycaemic agents, and the rest were already on oral hypoglycaemic agents and had developed poor diabetic control; four of these required insulin. Whole-body potassium was measured before treatment was begun (or altered) and again one and six weeks later. Whole-body potassium (ratio of observed to expected) was initially reduced in most of the patients requiring insulin. After control of diabetes whole-body potassium increased significantly in the three groups. The increase in whole-body potassium in the individual patients varied over a wide range, and in patients who were treated with insulin it was often of a similar magnitude to that observed in patients in diabetic ketoacidosis.

Ionic relations and electrical properties of isolated oocytes of Bufo bufo with special reference to removal of extracellular chloride

1. The efflux rate coefficients of sodium, potassium and chloride from immature oocytes of the toad Bufo bufo have been measured and found to be respectively, 0.0069, 0.0023 and 0.0034 min(-1).2. Replacement of external chloride by sulphate resulted in a fall in chloride efflux of about 50%. This has been interpreted in terms of exchange diffusion.3. The membrane conductance has been measured and found to be 0.14 x 10(-3) mhos cm(-2) in good agreement with the value calculated from the flux data, 0.12 x 10(-3) mhos cm(-2), after taking account of the chloride exchange diffusion fraction.

Renin, angiotensin, and norepinephrine in alloxan diabetes

The renin-angiotensin system and catecholamines were evaluated in short term alloxan diabetic rats which were either “severely diabetic” (polyuric with serum glucose > 450 mg. per 100 ml.) or “mildly diabetic” (normouric with serum glucose <450 mg. per 100 ml.). Plasma renin activity (PRA), renal renin activity (RRA), and the amount of angiotensin II producing an acute 10 mm Hg increase in blood pressure were all significantly decreased in the diabetic rats with this decrease correlating inversely with the severity of the diabetes. Insulin treatment of these rats resulted in partial normalization of angiotensin II responsiveness, PRA, and blood urea nitrogen. Injection of alloxan directly into the left renal artery did not decrease RRA. Protection of the left kidney during systemic alloxan injection did not prevent the decrease in renal renin activity. Streptozotocin-treated diabetic rats had increased vascular responsiveness to injected angiotensin II. Norepinephrine sensitivity (amount producing a 10 mm Hg increase in blood pressure) and norepinephrine stores (blood pressure response to tyramine) were normal in both alloxan- and streptozotocin-treated rats.

Blood volume as related to lean body mass was elevated in the severely diabetic rats thus suggesting one possible mechanism for the decrease in the renin-angiotensin system.

These results suggest that (1) norepinephrine responsiveness and norepinephrine stores are normal, and (2) there is suppression of RRA leading to decreased PRA and increased vascular reactivity to angiotensin II in the acutely diabetic alloxan-treated rat. Further, these abnormalities appear to be related to the degree of diabetes as assessed by serum glucose and twenty-four hour urine volume.

Total body potassium in long-term frusemide therapy: is potassium supplementation necessary?

Measurements of total body potassium (T.B.K.) were made by whole-body counting in four groups of patients receiving oral frusemide for one year. Patients in group 1 had essential hypertension and normal renal function and received 40 mg frusemide daily without potassium supplements. Patients in group 2 were similar but received oral potassium supplements for the first four months of treatment. Patients in group 3 had hypertension associated with renal disease and received 120 mg frusemide daily without potassium supplements. Patients in group 4 also had hypertension and renal impairment and in addition to 120 mg frusemide daily they received oral potassium supplements for four months. No evidence of depletion of T.B.K. was found in any of the groups after continuous treatment with frusemide for one year. It is questioned whether potassium supplementation in long term diuretic therapy with frusemide is necessary unless there is evidence of pre-existing potassium depletion or of some other factor such as cardiac failure, cirrhosis of the liver, or the nephrotic syndrome.

Assessment of potassium metabolism, using 42K, in cases of myxoedema before and after treatment with thyroxine

Total Exchangeable Potassium (TEK) was measured in 31 elderly patients admitted to a geriatric assessment unit. The value in control cases ranged between 26 mEq/kg to 45.5 mEq/kg; the mean values for men and women were 35.5 mEq/kg and 28.4 mEq/kg, respectively. The test was repeated after one week in eight cases, the standard deviation between the two estimations ranged from 0.35 to 1.13 with the exception of one case which was 2.55. Estimations were made in six cases of myxoedema, the initial value was low and on treatment rose by 22.6 per cent to 36.4 per cent which coincided with the clinical improvement.

Potassium transport and the relationship between intracellular potassium concentration and amino acid uptake by cells of a marine pseudomonad

Transport of K(+) by K(+)-depleted cells of marine pseudomonad B-16 (ATCC 19855) exhibited saturation kinetics. Rb(+) inhibited both K(+) transport and the K(+)-dependent transport of alpha-aminoisobutyric acid (AIB) into K(+)-depleted cells of the organism in proportion to the concentration of Rb(+) in the suspending medium. Inhibition of the K(+)-dependent uptake of AIB into K(+)-depleted cells by Rb(+) could be overcome by increasing the concentration of K(+) in the medium. When AIB and K(+) were added simultaneously to a suspension of K(+)-depleted cells, the uptake of K(+) occurred immediately and rapidly, whereas the accumulation of AIB occurred only after a lag. The initial uptake rate of AIB was directly proportional to the intracellular K(+) concentration. The intracellular concentration of K(+) and AIB at their steady-state levels increased to a maximum as the Na(+) concentration in the suspending medium was increased. At Na(+) concentrations between 0.2 and 0.3 M, the molar ratio of K(+) to AIB at their intracellular steady-state concentrations was constant at 1.6. At external Na(+) concentrations less than 0.2 M, the cells maintained a relatively higher K(+) intracellular steady-state level than AIB.

Comparison of regional myocardial perfusion determined by ionic potassium-43 to that determinated by microspheres

The ability of ionic potassium-43 ( 43 K) to reflect alterations in regional myocardial perfusion was determined by comparing the distribution of this tracer to that of labeled microspheres and flowmeter measurements under several conditions of coronary blood flow. When flow was normal, the regional distribution of ionic 43 K and labeled microspheres were similar. In ischemia induced by partial occlusion and pacing, both 43 K and microspheres showed the same decrease in activity (0.7 of control). When a coronary artery was completely occluded, both tracers were decreased to 0.3 of control. In other experiments, resting coronary blood flow was decreased by 25%, 50% and 75% as determined by flowmeter measurements. When this was done, regional distribution of ionic 43 K and microspheres both decreased in parallel but to a lesser degree than flowmeter data suggesting a contribution from collateral vessels. The endocardial/epicardial activity in the ischemic region also decreased proportionally. However, under conditions of increased flow during myocardial reactive hyperemia, 43 K activity (1.02 of control) did not increase to the same degree as microsphere activity (1.5 of control).

Potassium and amino acid transport in human leukocytes exposed to phagocytic stimuli

Influxes of potassium and amino acids were measured in suspensions of human polymorphonuclear leukocytes (PMNs) under resting conditions and after various phagocytic stimuli. Both ouabain-sensitive (or pump) and ouabain-insensitive (or leak) influxes of K were determined. In 5 mM external K, mean total K influx was 0.69 nmol/10(6) cells x min, of which 52% was ouabain-sensitive. Ouabain binding was irreversible, and, as in erythrocytes, was inhibited by K. At external concentrations of 0.1 mM, influxes of lysine and leucine were entirely carrier-mediated, with means of 0.021 nmol/10(6) cells x min, and 0.019 nmol/10(6) cells x min, respectively. After incubation of PMNs with zymosan or latex particles, the K pump was reduced more than 60%, whereas amino acid influxes were inhibited only by 30%. PMNs were also exposed to cytochalasin B before challenge by particles: the drug prevented phagocytosis but not surface binding of zymosan, nor did it influence transport of K or amino acids. After pretreatment of PMNs with cytochalasin B, interaction of zymosan with their surface resulted in the same degree of inhibition of influxes of K and amino acids as when the cells were permitted to phagocytose the particles. In contrast, exposure of PMN to latex particles, which do not bind to cytochalasin B-treated cells, after pretreatment of cells with cytochalasin B did not result in inhibition of influxes. Treatment of cells with colchicine had no effect on either membrane transport or its inhibition after exposure to various phagocytic stimuli. These results indicate that the surface membranes of PMNs are functionally heterogeneous with respect to the association of transport sites for the different solutes. Moreover, loss of specific membrane functions from phagocytosing cells may result from the surface-at-tachment phase of particle-cell interactions, since the interactions of zymosan particles with PMNs in the absence of phagocytosis also inhibited transport of solutes.

Functional separation of the Na-K exchange pump from the volume controlling mechanism in enlarged duck red cells

Previous publications have described a "volume controlling mechanism" in duck erythrocytes that returns both enlarged and shrunken cells to their original isotonic volume. Enlarged cells return to their original size by readjusting their K content. To study the specificity of this aspect of the mechanism for K, we prepared enlarged cells with various Na and K contents. Only cells containing a high K content resume their original size in the standard isotonic medium. The process of regulation resembles that described above. In contrast, cells containing a high Na content fail to reestablish this volume, but shrink instead until they reach a limiting minimal volume (four-fifths of normal). Here, another mechanism, the cation pump rather than the volume controlling mechanism, removes Na and is responsible for the changes in cell size. Enlarged cells with an intermediate Na and K content utilize both mechanisms to reduce their cation content. Only if Na is prevented from leaving the cell and sufficient K is present initially, will these cells reestablish their original size. These studies demonstrate that the cation pump and volume controlling mechanism function independently and, when cells enlarge, only K can effectively traverse the pathway associated with the volume controlling mechanism. This route differs from the one used by the cation pump to eject Na.

Transmural gradient of retrograde collateral blood flow in acutely ischemic canine myocardium

The contribution of retrograde coronary flow to total collateral flow was examined transmurally in anesthetized, open-chest dogs subjected to acute obstruction of the left anterior descending coronary artery. Regional coronary flow in normal and ischemic tissue was reflected by the tissue content of radioisotopes of potassium and rubidium and by radioactive microspheres. To measure total collateral flow, one isotope was administered when the retrograde cannula was clamped. The other isotope was administered when the cannula was opened to divert retrograde coronary flow away from acutely ischemic myocardium. Significant quantities of this isotope reached the ischemic region despite diversion of retrograde flow at an average rate of 3.5 ml/min. These results confirm earlier, but disputed, reports that total coronary collateral flow exceeds retrograde flow and are indicative of collateral pathways associated more closely with the microcirculation than with the larger epicardial arteries. Furthermore, the transmural distribution of myocardial blood flow in the ischemic tissue was altered nonuniformly by diversion of retrograde flow: 42 K or 86 Rb uptake was reduced to 25% of control in subepicardial tissue but only to 70% of control in subendocardial tissue. The transmural distribution of radioactive microspheres was similarly affected by diversion of retrograde flow. The results suggest that collateral pathways differ transmurally and may include significant luminal connections. Retrograde coronary flow is not a sensitive index of collateral flow to acutely ischemic subendocardial tissue.