Internal Potassium Concentration Research Articles

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Image: https://en.wikiversity.org/wiki/WikiJournal_of_Medicine/Medical_gallery_of_Blausen_Medical_2014#Cell_biologyT-cell activation depended on a critical range of internal potassium concentration; above this limit, T cells were suppressed. Potassium released from dying tumor cells promotes a protumor microenvironment, and normalizing intracellular potassium enhanced tumor clearance.Eil R,…, Restifo NP. Nature 2016 Sept 14 doi: 10.1038/nature19364.https://upload.wikimedia.org/wikipedia/commons/b/bf/PBB_Protein_AIRE_image.jpgPatients with AIRE deficiency lack central T cell tolerance. They produce high-affinity autoantibodies due to an ineffective T cell–dependent B-cell checkpoint that thwarts self-reactivity. However, such autoantibodies can be therapeutically valuable to combat autoimmune or inflammatory conditions.Meyer S,…, Hayday A. Cell 2016 July 28; 166:582–95.Image: Penny et al. Supplementary Fig. S1Altered retinoic acid metabolism was found to contribute to colonic inflammation and tumorigenesis. Restoring local colonic retinoic acid by preventing its catabolism in two different models of inflammation-driven colon cancer promoted protective immunity and reduced tumor growth.Bhattacharya N,…, Engleman EG. Immunity 2016 Sept 20; 45:641–655.Penny HL,…, Engleman E. Cancer Immunol Res 2016 Sept 16; doi: 10.1158/2326-6066.CIR-15-0038Image: “Tired Man” by József Somogyi.Intratumoral CD8+ T cells can become exhausted. Untangling the expressed genetic profiles of single CD8+ T cells revealed distinct signatures for activation and dysfunction. Metallothionein-regulated GATA-3 was found to be key to the dysfunction of intratumoral CD8+ T cells.Singer M,…, Anderson AC. Cell 2016 Sept 8; 166:1500–11.Image: Fig. 1C from Evans et al.Tumors with multiple neoepitopes respond to T-cell pressure by adapting and escaping. Although such immunoediting was not observed in a pancreatic tumor with few neoantigens, this reflected immune quiescence from poor tumor antigenicity. Introducing a neoantigen not only initiated a T-cell response but also restored the immunoediting phenotype.Evans RA,…, Vonderheide RH. J Clin Invest Insight 2016 Sept 8; e88328.doi: 10.1172/jci.insight.88328Image: 1F6A IgEFc bound to FcϵR1 http://www.rcsb.org/pdb/ngl/ngl.do?pdbid=1f6aExogenous IgE can be an adjuvant, but the role of endogenous tumor-specific IgE is less clear. Mice without IgE were more susceptible to tumors. IgE protection was mediated through the FcϵRI Fc receptor and dependent upon CD8+ T cells.Nigro EA,…, Vangelista L. J Immunol 2016 Aug 26. doi: 10.4049/jimmunol.1601026.

Regulatory role of charged clusters in the N-terminal domain of BetP from Corynebacterium glutamicum

The trimeric transporter BetP counteracts hyperosmotic stress by a fast increase in transport rate in order to accumulate the compatible solute betaine. The positively charged α-helical C-terminal domain acts as an osmosensor perceiving the increase in the internal potassium (K+) concentration. A second, still unidentified stimulus originates from stress-induced changes in the physical state of the membrane and depends on the amount of negatively charged lipids. BetP possesses a 60-amino acid (aa)-long negatively charged N-terminal domain, which is predicted to adopt a partly helical fold affecting osmoregulation by an unknown mechanism. It is assumed that the C-terminal domain, the N-terminal domain, and negatively charged lipids interact during stress sensing and regulation. Here, we have investigated the regulatory role of negatively charged clusters in the N-terminal domain. We identified one cluster, Glu24Glu25, to be crucial for osmoregulation. Cross-linking studies revealed an interaction between the C- and N-terminal domains of adjacent protomers modulating transport activation. A regulatory partner-switching mechanism emerges in which the C-terminal domain changes its interaction with the N-terminal domain of its own promoter and negatively charged lipids to an interaction with the N-terminal domain of an adjacent protomer and lipids bound to the central cavity of the BetP trimer.

Ionic regulation in the Antarctic nematode Panagrolaimus davidi, measured using electron probe X-ray microanalysis

The element composition of the pseudocoelomic fluid of the Antarctic nematode Panagrolaimus davidi was analysed by electron probe X-ray microanalysis after absorbing the fluid into Sephadex G-25 beads, and after producing calibration curves by analysing various concentrations of elements of interest absorbed into beads. The nematodes maintain higher concentrations of sodium and potassium in their pseudocoelomic fluid than in the external medium but lower concentrations of magnesium and calcium. When external concentrations of specific ions were elevated there was evidence for the regulation of internal concentrations of sodium, potassium, magnesium and chlorine. The time course of changes in response to exposure to elevated levels of KCl shows an increase in internal concentrations of potassium and chlorine up to 2h after exposure, followed by a decline. This is consistent with a model of ionic regulation proposed for Caenorhabditis elegans which suggests that high concentrations of ionic osmolytes are replaced by compatible organic osmolytes.

Potassium Starvation in Yeast: Mechanisms of Homeostasis Revealed by Mathematical Modeling

The intrinsic ability of cells to adapt to a wide range of environmental conditions is a fundamental process required for survival. Potassium is the most abundant cation in living cells and is required for essential cellular processes, including the regulation of cell volume, pH and protein synthesis. Yeast cells can grow from low micromolar to molar potassium concentrations and utilize sophisticated control mechanisms to keep the internal potassium concentration in a viable range. We developed a mathematical model for Saccharomyces cerevisiae to explore the complex interplay between biophysical forces and molecular regulation facilitating potassium homeostasis. By using a novel inference method (“the reverse tracking algorithm”) we predicted and then verified experimentally that the main regulators under conditions of potassium starvation are proton fluxes responding to changes of potassium concentrations. In contrast to the prevailing view, we show that regulation of the main potassium transport systems (Trk1,2 and Nha1) in the plasma membrane is not sufficient to achieve homeostasis.

Genetic alterations leading to increases in internal potassium concentrations are detrimental for DNA integrity in Saccharomyces cerevisiae

We have investigated the effects of alterations in potassium homeostasis on cell cycle progression and genome stability in Saccharomyces cerevisiae. Yeast strains lacking the PPZ1 and PPZ2 phosphatase genes, which aberrantly accumulate potassium, are sensitive to agents causing replicative stress or DNA damage and present a cell cycle delay in the G(1) /S phase. A synthetic slow growth phenotype was identified in a subset of DNA repair mutants upon inhibition of Ppz activity. Moreover, we observe that this slow growth phenotype observed in cdc7(ts) mutants with reduced Ppz activity is reverted by disrupting the TRK1 potassium transporter gene. As over-expression of a mammalian potassium transporter leads to similar phenotypes, we conclude that these defects can be attributed to potassium accumulation. As we reported previously, internal potassium accumulation activates the Slt2 MAP kinase pathway. We show that the removal of SLT2 in ppz1 ppz2 mutants ameliorates sensitivity to agents causing replication stress and DNA damage, whereas over-activation of the pathway leads to similar cell cycle-related defects. Taken together, these results are consistent with inappropriate potassium accumulation reducing DNA replication efficiency, negatively influencing DNA integrity and leading to the requirement of mismatch repair, the MRX complex, or homologous recombination pathways for normal growth.

The effects of soil chemical characteristics on the 134Cs concentrations in earthworms. Uptake from liquid medium

The concentrations of potassium, stable cesium, calcium and ammonium in soil, and of the pH are known to affect the uptake of 134Cs by plants and soil organisms. It is uncertain as to which extent this is a direct effect on the uptake of 134Cs (e.g. through competition for binding sites) or an indirect effect through a changing distribution of the 134Cs between the solid and liquid phase of the soil. Studying the effect of both varying concentrations of potassium, stable cesium, calcium and ammonium and the pH on the uptake of 134Cs by the earthworms Eisenia foetida and Lumbricus rubellus from solution was, therefore, a means to investigate this effect. The concentrations of 134Cs in the earthworms were found to differ by a factor of three between the species. Highest and lowest 134Cs concentration differed by a factor of five within each species. Potassium affected the 134Cs concentration in the earthworms significantly in contrast to stable cesium. However, the effects expressed per millimole added, were comparable for both elements. The non-significance of stable cesium might have been caused by the small concentration range used. Considering the natural concentrations of potassium and stable cesium in soil solution, addition of potassium was shown to be a more realistic countermeasure. No significant effects from varying pH or calcium and ammonium concentrations were observed. The internal calcium concentration increased with increasing calcium concentration in solution, whereas the internal potassium concentration was independent of the potassium concentration in the solution.

Evidence for a selective and electroneutral K+/H+-exchange in Saccharomyces cerevisiae using plasma membrane vesicles

The existence of a K+/H+ transport system in plasma membrane vesicles from Saccharomyces cerevisiae is demonstrated using fluorimetric monitoring of proton fluxes across vesicles (ACMA fluorescence quenching). Plasma membrane vesicles used for this study were obtained by a purification/reconstitution protocol based on differential and discontinuous sucrose gradient centrifugations followed by an octylglucoside dilution/gel filtration procedure. This method produces a high percentage of tightly-sealed inside-out plasma membrane vesicles. In these vesicles, the K+/H+ transport system, which is able to catalyse both K+ influx and efflux, is mainly driven by the K+ transmembrane gradient and can function even if the plasma membrane H+-ATPase is not active. Using the anionic oxonol VI and the cationic DISC2(5) probes, it was shown that a membrane potential is not created during K+ fluxes. Such a dye response argues for the presence of a K+/H+ exchange system in S. cerevisiae plasma membrane and established the non-electrogenic character of the transport. The maximal rate of exchange is obtained at pH 6·8. This reversible transport system presents a high selectivity for K+ among other monovalent cations and a higher affinity for the K+ influx into the vesicles (exit from cells). The possible role of this K+/H+ exchange system in regulation of internal potassium concentration in S. cerevisiae is discussed.

Mutants of Arabidopsis thaliana Capable of Germination under Saline Conditions.

Three mutant strains of Arabidopsis thaliana var Columbia were selected for their ability to germinate in elevated concentrations of NaCl. They were not more tolerant than wild type at subsequent development stages. Wild-type strains could not germinate at concentrations > 125 mM NaCl. Two of mutant strains, RS17 and RS20, could withstand up to 225 mM, whereas RS19 was resistant to 175 mM. The RS mutants could also germinate under even lower osmotic potentials imposed by high concentrations of exogenous mannitol (550 mM), whereas the effects of elevated levels of KCl, K2SO4, and LiCl were similar among the mutants and wild type. Therefore, the mutants are primarily osmotolerant, but they also possess a degree of ionic tolerance for sodium. Sodium and potassium contents of seeds exposed to high salinities indicated that the NaCl-tolerant mutants absorbed more of these respective cations during imbibition. These higher internal concentrations of potassium and sodium could contribute to the osmotic adjustment of the germinating seeds to the low osmotic potential of the external medium. Genetic analysis of F1 and F2 progeny of outcrosses suggest that the salt-tolerant mutations are recessive and that they define three complementation groups.

Determination of intracellular volume and internal solute concentrations of the green alga Chlorococcum submarinum

A method is described for measuring the cell volume of the unicellular green alga Chlorococcum submarinum, which depends on measurements of bromide concentration before and after disruption of the cells by ammonium hydroxide. Simultaneous equations are derived, which along with direct determination of cell water weight, allow the calculation of the intracellular volume in three different ways. The volumes calculated are in agreement indicating the validity of the method. The cell volumes and internal concentrations of glycerol, proline, potassium and sodium were determined for algae adapted to three salinities, 0.1, 0.5 and 1.0 M NaCl. The results showed that glycerol was the major internal solute and that the total measured solutes balanced the external osmotic pressure at all three salinities.

Characterization of the high‐affinity K+(Rb+)‐uptake system in roots of intact Taraxacum microspecies: comparison of 12 microspecies in relation to their mineral ecology

SUMMARY Taraxacum microspecies differ with respect to nutritional levels in their habitats. In the context of marked differences in growth response to internal potassium concentration between two ecologically contrasting microspecies, K+‐uptake characteristics, Vm and Km, of the high‐affinity uptake system of 12 microspecies were studied. In this comparative study, CaSO4‐pretreated plants were used.Microspecies differences in Vmax were more abundant than in Km. Significant differences between kinetic parameters of ecologically related groups of microspecies were largely absent; only the (average) Vmax of the group of microspecies derived from heavily fertilized and moist grasslands was higher than those of the remaining three groups of microspecies. Within a taxonomically related group of eight microspecies, variation in Vmax (average) and Km (average) values was almost as high as total variation. The results on kinetic characteristics of the high‐affinity K+‐uptake system are discussed in the context of additional differences in physiology such as the critical internal K+concentration and growth potential between two representative microspecies of different mineral ecology.

Influences of different external ion-concentrations on osmolality, internal potassium and sodium levels and uric acid concentration in Musca domestica larvae

1. l. Influences of increased salt concentrations in the rearing media on hemolymph osmolality, internal potassium, sodium and uric acid concentration were examined in third instar larvae of Musca domestica. 2. 2. The larvae are able to regulate their hemolymph osmolality which increases under osmotic stress to the characteristic osmolality of unloaded animals up to pupation. 3. 3. K +-concentration in the whole body directly follows the increased K +-content of the medium, but not in malpighian tubules, intestine, fat body and integument. 4. 4. The increased Na +-level in the whole body falls significantly behind the changed external Na +-concentration. 5. 5. Hyperosmotic conditions cause a correlative decrease of uric acid in the whole body and in the organs.

The ionic basis of the resting potential of molluscan unstriated muscle

The membrane potential (Vm) of unstriated, non-spiking fibres from the buccal retractor muscle of the opisthobranch molluscPhiline aperta is primarily determined by the distribution of the potassium ion across the membrane. In salines where potassium is varied and chloride remains constant or nearly so, the membrane potential varied with log external K+ with a slope of 50.6 (±2.3) mV per decade. In chloride-free salines the slope was 48.5 mV per decade. The experiments were conducted at temperatures of 18–20° C. A ten-fold reduction in external chloride concentration depolarised the fibres by around 10 mV, indicating that chloride permeability makes some contribution to Vm. In salines where [K]0·[Cl]0 is constant the Nernst slope was 55.8 mV per decade compared with the theoretical value of 58 mV. The experimental data suggest that the internal potassium concentration of the fibres is 247±31 mM and pNa/pK is 0.01, giving a predicted value of Vm in sea water of −72 mV. The membrane potential of 90 fibres measured in sea water was −74.2±1.3 mV. The membrane contains an electrogenic sodium pump which contributes 4–5 mV to the membrane potential.

Transient accumulation of potassium glutamate and its replacement by trehalose during adaptation of growing cells of Escherichia coli K-12 to elevated sodium chloride concentrations.

The sequence of events following the addition of 0.5 M NaCl to cells of Escherichia coli growing in a minimal mineral medium was investigated. Immediately after upshock the cells took up a large amount of K+ and synthesized approximately half the equivalent amount of glutamate concomitantly. After 30 min the cells started to synthesize trehalose, and after 2 h they had replaced most of their initial osmoprotectants by the carbohydrate. Cell trehalose was rapidly replaced by proline, taken up from the medium when added to the osmoadapting cells. The initial rate of this proline uptake was extremely rapid, and with rates observed of up to 0.6 mmol x min-1 x g-1 of cell protein it was approximately ten times faster than that reported in the literature for non-growing cells. These results indicate that for osmoadaptation of growing cells of E. coli the uptake of proline has priority over the synthesis of trehalose, which in its turn is preferred above K+ and glutamate as osmoprotectants. We observed that two mutants with unknown lesions, but which are known to be impaired in osmoadaptation, were inhibited in replacing K+ and glutamate by trehalose, indicating that this is the basis for their defect in osmoadaptation. Further experiments revealed that neither internal pH nor the membrane potential nor the transmembrane protonmotive force are likely to be involved in osmoadaptation in E. coli. However, during osmoadaptation a high internal potassium concentration appeared to stimulate the derepression of proline-uptake systems (mainly system ProP).

The requirements of cabbage and lettuce seedlings for potassium in the presence and absence of sodium

Abstract Sand culture experiments were performed in the glasshouse to determine the internal potassium concentrations required by lettuce and cabbage seedlings. Because the presence of sodium in the nutrient medium may have affected the potassium requirements, the experiments were repeated with and without sodium in the medium. The critical concentrations of potassium for maximum plant size varied as the plants grew larger because the potassium concentrations tended to increase over time. However, critical concentrations for maximum relative growth rate (RGR) were almost independent of time or plant weight. In the absence of sodium, the critical levels for a 10% reduction in RGR of cabbage was 2.2%K in the dry matter and for lettuce was 4.3%. In the presence of sodium, the corresponding critical levels were 0% and 1.0%, demonstrating that cabbage was more able to substitute sodium for potassium than was lettuce. Levels of sodium in commercial fields in the U.K. tend to be fairly low, suggesting that the c...

Osmotic regulation of transcription: induction of the proU betaine transport gene is dependent on accumulation of intracellular potassium.

The proU locus, which encodes a high-affinity betaine transport system, and the kdp operon, which encodes a potassium transport system, are the principal osmoresponsive genes in Escherichia coli and Salmonella typhimurium. The kdp operon is known to be induced in response to changes in cell turgor. We have investigated the control of proU expression and shown that it differs from that of kdp in a number of fundamental ways. Rather than responding to changes in turgor, proU expression is principally determined by the intracellular accumulation of potassium ions. Potassium and betaine were shown to play distinct osmoprotective roles. Potassium serves as the principal osmoprotectant and is accumulated in response to low-level osmotic stress to restore turgor. As external osmolarity is increased to a level at which the corresponding increase in internal potassium concentrations is potentially deleterious to enzyme function, betaine (when available) is accumulated in preference to potassium. The different mechanisms of proU and kdp regulation reflect the different physiological roles of these two osmoprotectants.

Transient proton inflows during illumination of anaerobic Halobacterium halobium cells

In Halobacterium halobium strain R 1 containing both bacteriorhodopsin (bR) and halorhodopsin (hR), the light-driven proton uptake has been experimentally resolved into three transient inflows which are superimposed on the larger proton outflow. Under anaerobic conditions the early proton uptake consists of two components: (i) an inflow which can be blocked using the ATPase inhibitor, Dio-9, and (ii) an inflow which can be abolished by low concentrations (<125 n m) of triphenyltin chloride (TPT) with no inhibition of ATP synthesis. At pH 6 these two inflows are approximately equal in magnitude and duration. Measurements of buffering capacity and internal pH indicate that Dio-9 does not alter the passive proton-hydroxyl permeability of the cell membrane and that TPT at these low concentrations slightly decreases it. At later times of illumination (iii) another transient light-driven proton inflow occurs. This inflow is most evident during the first illumination after cells have been stored for extended times in the dark. The internal potassium concentration is not changed by storage, but apparently sodium is taken up, and we attribute the third inflow to sodium extrusion in exchange for protons. These results demonstrate the existence of three distinct triggered secondary proton inflows through the cell membrane. The proton inflow, which can be inhibited by Dio-9, correlates with proton-dependent ATP synthesis. The second inflow, which disappears in the presence of low TPT concentrations, is a passive proton uptake through an otherwise unidentified channel in response to electrogenic chloride pumping by bacteriorhodopsin and/or halorhodopsin. The third system correlates with the Na + H + antiporter function that has been demonstrated in H. halobium cell envelope vesicles. In contrast to observations on hR-containing vesicles, which can develop substantial Cl − gradients, the electroneutral OH − Cl − exchange function can be demonstrated in intact cells only at TPT concentrations >500 n m.

Intracellular potassium concentration and relative acidity of the ribosomal proteins of methanogenic bacteria

The intracellular potassium concentration and percentage of acidic ribosomal proteins were determined for nine methanogenic bacteria representing diverse phylogenetic groupings. Representatives of the Methanobacteriaceae family possessed very high internal potassium concentrations: Methanobrevibacter arboriphilus, 1225 mM; Methanobrevibacter smithii, 1065 mM; Methanobacterium thermoautotrophicum, 1103 mM; Methanobacterium bryantii, 861 mM; and Methanobacterium strain G2R, 886 mM. Members of other families tested maintained much lower internal concentrations of potassium. Methanosarcina barkeri (family Methanosarcinaceae) and Methanospirillum hungatei (family Methanomicrobiaceae) maintained approximately 200 mM internal potassium, while Methanococcus voltae (family Methanococcaceae) possessed an intermediate concentration of 725 mM. Those organisms maintaining the highest internal potassium concentrations also had the largest number of acidic ribosomal proteins. There appeared to be a correlation among the phylogenetic placement of the organism (based on 16S rRNA sequence data), its content of intracellular potassium, and the percentage of acidic ribosomal proteins. Those methanogens most closely related to extreme halophiles possessed the highest concentrations of internal potassium and had an increased percentage of acidic ribosomal proteins, both properties of halophilic bacteria.

SOME ASPECTS OF THE PHYSIOLOGY AND BIOCHEMISTRY OF MARINE FUNGI

Summary1. This review deals with certain aspects of the physiology and biochemistry of marine fungi. Though it is not easy to define what is meant by a marine fungus, the information presented here relates to those species that by consensus can be accepted as being truly marine. The material is in two parts, that relating to the higher fungi (Ascomycotina, Basidiomycotina and Deuteromycotina) and that relating to the lower fungi, particularly those zoosporic fungi that require sodium for growth.2. Higher marine fungi appear to have a similar carbon, nitrogen and vitamin nutrition to their terrestrial counterparts.3. Growth of higher marine fungi can be optimal in 100% sea water, but more frequently optimal growth is at a lower percentage. The percentage giving optimal growth may be determined by the rate of ion uptake required to generate the necessary turgor for growth. The tolerance of the vegetative phase of many terrestrial fungi to salinity appears little different from that of marine fungi. In general, members of the Basidiomycotina are particularly sensitive to salinity, while those of the Ascomycotina and Deuteromycotina are much more tolerant.4. The degree of tolerance to salinity may be dependent upon temperature and whether or not adaptation by the fungus has occurred.5. Maintenance of a suitable internal potassium concentration by a higher marine fungus is important for growth in a saline medium. Calcium appears to be necessary for the retention of potassium and organic solutes within the hyphae.6. It appears that higher marine fungi are able to maintain a ratio of potassium: sodium higher than that of sea water by the presence of a plasma membrane ATPase which may have a higher pH optimum than the equivalent enzyme from terrestrial counterparts.7. Higher fungi produce more glycerol as the salinity of the external medium is increased. Whether or not the compound is involved in osmoregulation has yet to be determined.8. Turgor is thought to be generated in higher marine fungi growing in sea water by organic solutes (predominantly glycerol and arabitol) and by ions, with the latter playing the major role. Though interpretation of the data depends on several assumptions, the high concentrations of sodium that seem likely to be present in hyphae or cells have implications for the activity of enzymes, if they have similar properties to those of higher plants. There is a need for information on the effects of high concentrations of ions on enzymes located in the cytoplasm of higher fungi.9. In spite of some experimental uncertainties, it seems that reproduction and spore germination of higher marine fungi are very much less affected by salinity than are the same processes of terrestrial counterparts.10. The zoosporic marine fungi require sodium for growth. Though the ion is required at high concentration for growth, sodium cannot be replaced by potassium. Evidence indicates that sodium is involved in the transport of solutes across the plasma membrane.11. The carbon and nitrogen requirements for the growth of the zoosporic marine fungi demand further investigation, particularly at the biochemical level. There is evidence that the respiration of these fungi possesses many interesting features.12. Vitamin requirements of the zoosporic marine fungi depend on the isolate under investigation. Vitamin B., does not now seem to be an obligatory requirement. The ability of phospholipids and sterols to stimulate growth requires further investigation.13. Further studies on marine fungi in the laboratory should focus particularly on growth in continuous culture. Physiological and biochemical studies would be helped by more precise guidance from those concerned with the ecology of these fungi.

The interaction of potassium with the activation of anomalous rectification in frog muscle membrane.

1. Inward rectification of frog muscle membrane was analysed with the Vaseline gap method. 2. Hyperpolarization, under voltage clamp, produced inward potassium currents, which had a component that activated with a time constant, tau K. 3. The activation time constant tau K of the inward potassium currents was voltage dependent. For a given external potassium concentration, the time constant was maximal for potentials near the potassium equilibrium potential, EK. 4. The potassium chord conductance gK, had a sigmoidal voltage dependency, increasing initially e-fold per 11.6 mV of hyperpolarization. 5. When the internal potassium concentration was fixed, raising external potassium induced a shift of the tau K-V and the gK-V relations in the positive direction along the voltage axis. That shift was comparable to the change in EK. 6. No shift of the tau K-V and the gK-V relations was observed when the internal potassium was reduced from 150 to 50 mM. 7. Changes of internal sodium concentration between 5 and 100 mM did not significantly effect the magnitude of inward rectification.

Effects of internal and external sodium on the sodium current-voltage relationship in thesquid giant axon

The early transient current-voltage relationship was measured in internally perfused voltage clamped squid giant axons with various concentrations of sodium on the two sides of the membrane. In the absence of sodium on either side there is an outward transient current which is blocked by tetrodotoxin and varies with internal potassium concentration. The current increases linearly with voltage for positive potentials. Adding sodium ions internally increases the slope of the current-voltage relationship. Adding sodium ions externally also increases the slope between +10 and +80 mV. Adding sodium to both sides produces the sum of the two effects. The current-voltage relationships were fit by straight lines between +10 and +80 mV. Plotting the extrapolated intercepts with the current axis against the differences in sodium concentrations gave a straight line, Io = -P (Co-Ci)F. P, the Fickian permeability, is about 10(-4) cm/sec. Plotting the slopes in three dimensions against the two sodium concentrations gave a plane g = go + (aNao + bNai)F. a is about 10(-6) cm/mV-sec and b about 3 x 10(-6) cm/mV-sec. Thus the current-voltage relationship for the sodium current is well described by I = -P(Co-Ci)F+ (aco + bci)FV for positive potentials. This is the linear sum of Fick's Law and Ohm's Law. P/(a + b) = 25 +/- 1 mV (N = 6) and did not vary with the absolute magnitude of the currents. Within experimental error this is equal to kT/e or RT/F. Increasing temperature increased P, a and b proportionately. Adding external calcium, lithium, or Tris selectively decreased P and a without changing b. In the absence of sodium, altering internal and external potassium while observing the early transient currents suggests this channel is more asymmetric in its response to potassium than to sodium.