The role of lactate in the active excretion of sodium by frog muscle

A comparison of solutions for lung preservation using pulmonary alveolar type II cell viability

Many special solutions have been developed to protect the ischemic lung in preparation for transplantation. To determine an effective solution, we isolated pulmonary alveolar type II cells from rat lungs. These cells play an important role in sodium transport and the production of surfactant; thus, they are crucial to the respiratory physiology of the lung. In this study, we examined in vitro the effect of various solutions such as Collins' solution, Collins-Sacks solution, and glucose-insulin-potassium solution on alveolar type II cell viability. The cell viability was examined with a trypan blue dye exclusion test and [3H]thymidine uptake proliferation assay after 24 and 72 hours of incubation. The alveolar type II cells in the glucose-insulin-potassium solution had greater viability compared with cells cultured in either Collins' or Collins-Sacks solution. This study demonstrates that glucose-insulin-potassium solution has the least toxic effect on isolated alveolar type II cells compared with other preserving solutions.

Relationship between ionic surroundings and insulin actions on glucose transport and Na,K-pump in muscles

1. It is well known that insulin has various effects on glucose transport and the Na,K-pump in muscles. It is also known to have some effects on the membrane potential--in general, insulin induces a hyperpolarization of the membrane in muscles. Furthermore, it is suggested that the actions of insulin are modified by changes in ionic surroundings. 2. In this review article, the actions of ionic surroundings and insulin on glucose transport in muscles are discussed; in particular, the effects of changes in extracellular and/or intracellular concentrations of Na, K, Ca and H ions will be mentioned. 3. The actions of ionic surroundings and insulin on the Na,K-pump in muscles are discussed; in particular, the effects of changes in extracellular an/or intracellular concentrations of Na, K, Ca and H ions will be examined. 4. The relationship between the actions of ionic surroundings and insulin are discussed. 5. In particular, the effects of changes in ionic surroundings on the insulin-induced hyperpolarization of the membrane are discussed by relating it to the Na,K-pump function. The relationship between the insulin-induced change in membrane potential and glucose transport will be also mentioned.

Transport of electrolytes in muscle

The muscle fiber stands alongside the red blood cell and the giant axon as one of the three classical cell types that have had major application in investigating ion transport processes in cell membranes. Of these three cell types, the muscle fiber was the first to provide definite evidence for a sodium pump. The ability of the sodium pump to produce an electrical potential difference across the cell membrane was also first demonstrated in muscle fibers. This important property of the sodium pump is now known to have physiological significance in many other types of cells. In this review, electrolyte transport investigations in skeletal muscle are traced from their inception to the current state of the field. Applications of major research techniques are discussed and key results are summarized. An overview of electrolyte transport in muscle, this article emphasizes relationships between the muscle fiber membrane potential and ionic transport processes.

Mechanism of insulin action on resting membrane potential of frog skeletal muscle

At a concentration that stimulates the Na pump, insulin hyperpolarizes the plasma membrane of frog sartorius in the presence of substrate-free Ringer. The hyperpolarization ranged from 3.5 to 7.3 mV and averaged 4.7 mV. Ouabain, 10(-4) M, completely blocked the effect of insulin on the membrane potential. Moreover, ouabain completely reversed the insulin-induced hyperpolarization within 20 min. The hyperpolarization produced by insulin was not associated with a detectable increase in the ratio of K+ permeability to Na+ permeability nor with a detectable increase in the concentration of intracellular K+, although a depletion of K+ near the external surface of the membrane cannot be excluded. The results clearly indicate that the hyperpolarization is secondary to stimulation of the Na pump by insulin.

Biphasic effects of insulin and ouabain on fluid transport across rabbit corneal endothelium

1. Low levels of insuling stimulate transendothelial fluid transport from preswollen stroma to aqueous in rabbit corneal preparations. The rate of stromal thinning at the end of the first hour averages 30% faster with insulin, 3.5 x 10(-22) M (4.8 micromicron/ml.), than that of the paired control. This concentration is about the physiological level in rabbit aqueous. 2. The stimulation with insulin is transient. Rates of thinning average higher but not significantly different from control rates by the second hour. 3. High levels of insulin between 3.5 x 10(-9) M (480 micromicron/ml.) and 2.0 x 10(-6) M (2.75 X 10(5) micromicron/ml.) inhibit fluid transport. The inhibition at the low end of this range of concentrations becomes more pronounced with longer perfusion times but appears not to exceed ca. 50% of the control rate. 4. Ouabain also induces a biphasic effect on fluid transport which is characteristically different from that with insulin. The maximal stimulation observed at all times occurred with a fixed concentration of 10(-10) M. The stimulation is not transient but increases throughout the duration of the perfusion; the average rate is elevated 50% above the control rate by the third hour. 5. The transition from a stimulatory to an inhibitory effect occurs consistently at ca. 10(-8) M with ouabain, while a similar transition with insulin occurs at ca. 10(-9) M and appears to shift towards slightly higher concentrations during a 3 hr perfusion period. 6. Inhibition of fluid transport with ouabain, 3 x 10(-7) M, is increased from ca. 50% after 1 hr to more than 70% at the end of the third hour of perfusion. 7. The combined presence of stimulatory concentrations of ouabain and insulin affects tromal thinning in a manner resembling the effect of ouabain alone more than that of insulin; additive effects could not be discriminated. Progressively raising the concentration of insulin to a level (10(-8) M) that alone inhibits stromal thinning, ultimately abolishes the stimulatory effect of ouabain. Based on other evidence and current models of drug/hormone-membrane interaction, these results can be interpreted to indicate a concentration-dependent interaction between receptor complexes of ouabain and insulin with (Na+ + K+)-ATPase.

The effect of insulin on the transport of sodium and potassium in rat soleus muscle

1. The action of insulin on the transport and the distribution of Na and K has been studied in rat soleus muscles incubated at 30 degrees C in glucose-free Krebs-Ringer bicarbonate buffer. 2. Measurements of the uptake and the wash-out of 22Na indicate that the muscles contain an intracellular pool of Na available for transport which is confined to the water space not available to sucrose. Ouabain (10(-4)-10(-3)M) inhibited 22Na efflux by 69% (0-287 micronmole/g tissue wet weight per minute) and 42K-influx by 40% (0-196 micronmole/g tissue wet weight per minute). When all extracellular Na was replaced by Li, both 22Na-efflux adn 42K-influx were inhibited to about the same extent and ouabain produced very little further inhibition. 2,4-dinitrophenol decreased the ouabain-resistant component of 22Na-efflux by 39%. 3. Insulin (from 0-1 to 100 mu./ml.) increased the rate coefficient of 22Na-efflux by from 11 to 46% within 15 min. In the presence of ouabain (10(-3)M), the same relative increase was obtained, indicating that the hormone stimulates the glycoside-sensitive and the glycoside-insensitive Na transport to a similar extent. The effect of insulin on 22Na-efflux was not abolished by tetracaine (0-5 X 10(-3)M), phlorizin (0-5 X 10(-2)M) or by the substitution of Na, K, Mg or Ca. In the presence of 2,4-dinitrophenol (0-5 X 10(-4)M) or at temperatures below 15 degrees C, the hormone produced no detectable change in 22Na-efflux. 4. Insulin increased 42K-influx from 0-525 to 0-664 mumole/g tissue wet weight per minute. This effect was entirely blocked by ouabain but not by tetracaine. Insulin produced a 14% transient decrease in 42K-efflux. 5. The continued exposure to insulin led to a new steady state, in which the intracellular Na pool was decreased from around 10 to around 5 mumole/g tissue wet weight and the K content increased by an equivalent amount. In the presence of ouabain or at low extracellular concentrations of K, insulin increased the rate of 22Na-influx by around 35%. This effect was blocked by 2,4-dinitrophenol but not be tetracaine. 6. It is concluded that insulin stimulates the active coupled transport of Na and K, possibly by increasing the relative Na-affinity of the system mediating this process.

The membrane potential of rat diaphragm muscle fibres and the effect of denervation

1. Resting membrane potentials of rat diaphragm muscles were measured in vitro after previous denervation for 0-10 days. In some experiments denervated muscles were incubated in vitro for 3 hr while in others they were cultured for 15-24 hr to allow adequate exposure to drugs before recording. 2. It was found that resting membrane potentials, within 2-5 mm of the site of nerve section were significantly lower, within 3 hr, than resting membrane potentials measured more than 9 mm away from site of nerve section. This difference could be reduced or abolished by bathing preparations in solutions containing adrenaline (10 muM), noradrenaline (10 muM) or isoprenaline (10 muM) or dibutyryl cyclic AMP (10 muM-0-25 mM in the presence of 2 mM theophylline). Cyclic AMP (0-5 mM) was ineffective. 3. Application of solutions containing dibutyryl cyclic AMP for 3 hr also raised the resting membrane potential of muscles denervated 4-5 days previously. Culture studies showed that this effect was sustained when the time of incubation was 24 hr. 4. Incubating freshly denervated preparations with cycloheximide (22 mug/ml.) or actinomycin D (1 mug/ml.) did not prevent the development of the early (3 hr) fall in resting membrane potential despite a concomitant inhibition of RNA or protein synthesis. Culturing freshly denervated muscles in solutions containing cycloheximide (10 or 25 mug/ml.) which blocked 93% of protein synthesis, did not prevent the expected drop in resting membrane potential after 15 or 24 hr. 5. It was found that exposure to ouabain (1 or 5 mM) produced a rapid (15 min) fall in resting membrane potential in innervated and denervated preparations treated with dibutyryl cyclic AMP but not denervated preparations. After 5 days denervation cyclic AMP levels in muscle were increased by about 40%. 6. It is suggested that upon denervation an electrogenic action of a NA+-pump is blocked and that dibutyryl cyclic AMP and catecholamines are capable of stimulating this pump.

Contribution of an electrogenic sodium pump to membrane potential in mammalian skeletal muscle fibres

1. Relationship between the resting membrane potential and the changes in the intraceullar Na and K concentrations ([Na]i and [K]i) was studied in 'Na-loaded' and K-depleted' soleus (SOL) muscles of rats which had fed a K-free diet for 40 and more days. 2. The extracellular space of the muscles was not significantly different between normal and K-deficient rats. The inulin space in both the 'fresh' and Na-rich' muscles can be determined by the same function relating the space to the muscle weight. 3. Presence of 2-5-15 mM-K in the recovery solution hyperpolarized the 'Na-rich' muscul fibres at the beginning of recovery. The hyperpolarized membrane potential exceeded, beyond the measured potential of 'fresh' muscle fibres, the theoretical potential derived from the ionic theory, or even beyond Ek. Then, the measured membrane potential declined progressively during the immersion in a recovery solution and returned to the steady-state value When a considerable Na extrusion and K uptake took place, the measured membrane potential became equal to Ek. 4.he maximal hyperpolarization occurring immediately after immersion in the recovery solution became smaller and had a shorter duration when increasing the external K concentration ([K]o) from 2-5 to 15mM. 5. The K-sensitive hyperpolarization was completely abolished on exposure to 0mM [K]o, on cooling to ca. 4 degrees C, and in the presence of oubain (10(-4) M). The inhibitory effects were reversed on returning to the control conditions. The membrane potential obtained after inhibition of the electrogenic Na-pump with cooling or ouabain agrees well with that predicted by the 'constant-field' equation. 7. The external Cl ions had a short-circuiting effect on the electrogenic Na-pumping activated on adding K ions. 8. The replacement of Na ions in a recovery solution with Li ions resulted in a faster rate of depolarization from the maximal hyperpolarizationp. It is concluded that the resting membrane potential of 'Na-loaded' and 'K-depleted' SOL muscle fibres is the sum of an ionic diffusion potential predicted by either the Nernst equation or the constant-field equation and of the potential produced by an electrogenic Na-pump.

Effect of insulin upon the sodium pump in frog skeletal muscle

1. Insulin increased the rate of net Na extrusion from Na-loaded frog skeletal muscle into glucose-free Na-Ringer. After a 90 min period of efflux, the insulin-treated muscles contained approximately 11% less intracellular water than did their controls. This decrease in intracellular water resulted in an increase in the concentration of intracellular K, [K(+)](i), even though there was no definite effect upon net K flux. In spite of the decrease in intracellular water, [Na(+)](i) was lower in those muscles treated with 500 m-u. insulin/ml. than in the controls.2. Insulin consistently increased (22)Na efflux into Na-Ringer containing either 10 or 2.5 mM-K(+). This effect was reversible and was not produced by other proteins.3. Acetylstrophanthidin (5 x 10(-6)M) blocked all or nearly all net Na efflux even in the presence of insulin. The presence of this concentration of acetylstrophanthidin or of K-free Na-Ringer inhibited the effect of insulin upon (22)Na efflux from Na-loaded muscles.4. All of the above results indicate that insulin in some way increases the activity of the Na pump. The inhibition by K-free Na-Ringer also suggests that this is not due to production of additional pump sites.5. Insulin also increased (22)Na efflux and net sodium efflux into Li-Ringer. When the new steady-state was reached after addition of insulin, the (22)Na kinetics still obeyed a power relation to intracellular (22)Na. However, in every single case, insulin resulted in a decrease of approximately 18% in the exponent, n.6. Curve-fitting of the kinetic data to equations based upon a three-site model of the Na pump suggests that insulin increases the affinity of the sites toward Na(+). In terms of Eisenman's theory of ion selectivity, this would indicate an increase in the anionic field strength of the Na-carrying sites and also predict that the increase in affinity for H(+) would be greater than that for Na(+). This latter prediction is entirely consistent with the observed decrease in n.7. The results suggest that insulin may be increasing H(+) efflux as well as Na(+) efflux and thereby may be increasing intracellular pH. It is suggested that some of the intracellular effects of insulin might be mediated by such an effect.

Insulin, glucose, and potassium in the treatment of congestive heart failure

A daily infusion of 500-1,000 ml of 50% glucose containing 100-120 units of soluble insulin and 100-120 mEq of potassium chloride per litre was given to six patients suffering from hyponatraemia and congestive cardiac failure resistant to digoxin and diuretic therapy. In two patients there was no response, but four showed a striking improvement with a sodium and water diuresis, a rise in plasma sodium level, and in two cases a reversion from atrial fibrillation to sinus rhythm. It is suggested that insulin, glucose, and potassium given by the intravenous route in adequate dosage forms a useful adjunct to the management of severe congestive heart failure.

Ionic permeability changes as the basis of the thermal dependence of the resting potential in barnacle muscle fibres

1. The thermal dependence of the resting potential of isolated barnacle muscle fibres was larger (1-2 mV/ degrees C) than predicted by Nernst's equation (about 0.2 mV/ degrees C). A comparative study was made of the influence on thermal dependence of parameters related to (a) passive permeability and to (b) Na extrusion.2. High [K](o) decreased the thermal dependence reversibly. [K(i)], [Na](i) and [Cl](i) were determined by chemical analysis, and Goldman's equation was fitted to data relating V to [K](o) at different temperatures, in the presence and absence of ouabain 5 x 10(-5)M. In both cases the behaviour of V when T was lowered from 20 to 4 degrees C was accounted for by increases in the calculated P(Na/PK) and P(Cl/PK) (from 0.006 to 0.043 and from 0.17 to 0.34 on the average, respectively.)3. Other parameters related to passive permeability (and which caused reversible depolarization): decreased [Cl](o) (methanesulphonate or gluconate substituted), and decreased pH(o) (below 5.0), also decreased the thermal dependence reversibly.4. Inhibitors (ouabain 5 x 10(-5)M, cyanide 2-10 x 10(-3)M, 2,4-dinitrophenol 2 x 10(-4)M) externally applied did not affect either resting potential or its thermal dependence for several hours.5. Increasing [Na](i) three- to fourfold by intracellular injection decreased both resting potential and its thermal dependence.6. Although a small effect by a Na electrogenic pump cannot be excluded, the largest part of the thermal effect on the resting potential is concluded to depend on temperature-induced variations in relative ionic permeabilities to cations and anions. A model is proposed which can account for the data assuming that (a) each permeant ion associates to a separate site in the membrane, and (b) the ion-site equilibrium is temperature-dependent.

Sodium fluxes in diaphragm muscle and the effects of insulin and serum proteins

1. Thin diaphragm muscles in dialysed serum maintained their total sodium at values similar to those found in vivo. The fibre sodium exchanged with a half-time of 5 min, and the flux was 10 p-mole.cm(-2).sec(-1). The internal sodium was less than 10 mumoles/g fibre water and the ratio of external to internal sodium was at least 15. The calculated energy expenditure for sodium extrusion was less than 2% of the resting metabolism.2. In physiological saline the half-time for exchange of fibre sodium was similar to that in serum, but in saline there was an increase in sodium permeability and a raised total and fibre sodium.3. Muscles treated with insulin (0.02 u./ml.) showed a more rapid exchange of sodium compared with muscles in saline, with no change in the permeability to sodium. Insulin also affected sodium movements in the absence of external glucose.4. In saline the fraction of sodium which exchanged rapidly occupied 0.33 by volume of the muscle, after corrections for diffusion, and this value was similar to the mannitol space.5. Fibre diameters were measured in frozen sections. Muscles prepared by fixation and embedding showed marked shrinkage.

The relation between sodium ion content and efflux of labelled sodium ions from yeast

1. The activity of the Na(+) pump in an Na(+)-rich yeast was compared with that in an Na(+)-rich frog sartorius muscle, and found to be very similar to it over the first hour if both were immersed in fluid containing 104mm-Na(+) plus 10mm-K(+). 2. The efflux of labelled Na(+) from an Na(+)-rich yeast into an Na(+)-free medium was investigated. In this Na(+)-free medium, Li(+) or choline replaced the Na(+), and the efflux-content curves obtained with either of these ions were very similar. The curves were sigmoid, reaching or approaching a saturation at the higher internal Na(+) concentrations. 3. The curves obtained with yeast resembled those similarly obtained with frog sartorius muscle by Keynes & Swan (1959), Mullins & Frumento (1963), Harris (1965) and Keynes (1965). The slope of the plot of the logarithm of the Na(+) efflux against the logarithm of the Na(+) concentration in the cells reached its highest value at an internal Na(+) concentration of 15m-equiv./kg. (27m-equiv./l. of cell water). 4. The effect of external K(+) concentration on the efflux-content relationship was examined. An increased K(+) concentration was found to increase the Na(+) efflux by raising the saturation value, which is similar to observations made by Harris (1965) with frog muscle. 5. The effect of increasing the external carbon dioxide concentration was investigated. No effect on the slope of the plot of the logarithm of the Na(+) efflux against the logarithm of the Na(+) content was noticed even when the yeast suspension was equilibrated with 100% carbon dioxide. There was, however, a decrease in the amount of Na(+) efflux on equilibrating the solution with carbon dioxide.

Cytochemistry of phosphatases of the sarcoplasmic reticulum. I. Biochemical studies

A microsomal fraction was isolated from rabbit psoas muscle by a modification of Muscatello's method. The fraction contained a Mg-dependent ATPase which had a pH optimum of 7.5. Activity was further stimulated by addition of Na or K or other monovalent cations to the reaction mixture, but synergistic activation by Na and K, and ouabain inhibition, could not be demonstrated. The enzyme hydrolyzed only ATP (adenosine triphosphate) and ITP (inosine triphosphate) at appreciable rates, but Na or K stimulated activity only when ATP was used as substrate. Activity was inhibited by Ca and by low concentrations of Na deoxycholate, and was sensitive to inhibition by thiol group reagents. The enzyme could be distinguished from another enzyme, also present in the fraction, which was Ca-activated, and which exhibited a wider substrate specificity, different pH activation characteristics, lower specific activity, lack of stimulation by Na or K, and less sensitivity to inhibition by deoxycholate and by thiol group reagents. These findings formed the basis for demonstration of the Mg-dependent ATPase in situ.

Active transport of sodium and potassium in mammalian skeletal muscle and its modification by nerve and by cholinergic and adrenergic agents

1. Active transport of Na(+) and K(+) by Na-rich extensor digitorum and soleus muscles of rat was found to be increased considerably when muscles were innervated during enrichment with Na(+) in K-free modified Krebs solution containing 160 mM-Na at 2 degrees C and recovery in a similar fluid with 10 mM-K and 137 mM-Na at 37 degrees C, bubbled with oxygen.2. Addition of acetylcholine (2.0 mug/ml.) to recovery fluid containing denervated extensors increased active transport, whereas addition of eserine (50 mug/ml.), decamethonium (0.1 mug/ml.) and to a lesser extent tubocurarine (0.26 mug/ml.) inhibited active transport. Blocking of nerve conduction in innervated extensor inhibited K(+) uptake more than Na(+) excretion.3. The membrane potential of Na-rich extensor muscles measured soon after re-immersion in recovery fluid was higher in denervated than in innervated muscles. In the latter it was close to the K-equilibrium potential (E(K)). It is suggested that denervation here makes the Na-pump electrogenic by decreasing K(+) uptake either by decreased permeability or by inactivating a K-pump. Evidence is presented that the latter is more likely.4. Addition of isoprenaline to Na-rich soleus muscles in recovery fluid increased active transport and reduced the membrane potential measured soon after re-immersion in recovery fluid. The Na-pump still remained electrogenic in the presence of isoprenaline. It was suggested that isoprenaline might also stimulate the Na-pump, perhaps through activation of lactic dehydrogenase.

Effect of insulin on potassium flux and water and electrolyte content of muscles from normal and from hypophysectomized rats

It was reported previously that insulin hyperpolarized rat skeletal muscle and decreased K(+) flux in both directions. The observations on K(+) flux are now extended to take advantage of the greater sensitivity to insulin of hyperphysectomized rats. Insulin caused a shift of water from extracellular to intracellular space if glucose was present, but not in its absence. Insulin caused net gain of muscle fiber K(+), though not necessarily an increase in K(+) concentration in fiber water. It probably also decreased intrafiber Na(+) and Cl(-). Insulin decreased K(+) efflux. The effect was dose-dependent. Muscles from hypophysectomized rats were more sensitive to the action of insulin on K(+) flux than were those from normal rats. The effect was demonstrable within the time resolution of the system, suggesting that insulin's action is on cell surfaces. K(+) influx was also decreased by insulin. Bookkeeping suggests that some K(+) influx be called active. Insulin seemed to decrease active K(+) influx and passive K(+) efflux. It is not resolved whether insulin has a true dual effect or whether it acts only on passive fluxes in both directions (the apparent action on active K(+) influx being an artefact of incomplete definition of passive flux) or whether a single alteration in the membrane may affect both active and passive fluxes.