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.     

Possible role of Ca ions in the resting metabolism of frog sartorius muscle during potassium depolarization

Oxygen consumption and Ca exchangeability at different levels of potassium depolarization were studied in frog sartorius muscle. It was found that the changes in oxygen consumption parallel the changes in Ca exchangeability. Procaine (10^?3 M) and CaCl₂ (2.10?2 M) suppressed both extra oxygen consumption and Ca exchangeability at low values of depolarization. At higher values of depolarization procaine and CaCl₂ differed in their action. Procaine favored inhibition of these processes, CaCl₂ caused their activation. The effects of these compounds was not a result of a change in the membrane potential, since their effect on potassium depolarization was found to be small. Relations between oxygen consumption and Ca exchangeability similar to those observed at potassium depolarization seem to exist under conditions where caffeine was applied. It is proposed that the extra oxygen consumption caused by potassium depolarization or on application of caffeine and unaccompanied by mechanical changes is related to the release of Ca from its bound form. Oxygen consumption in isotonic sucrose solution was also studied, but some different data from the above were obtained.     

Structural organization of chromatin as a factor determining the rate of its endonucleolysis in irradiated and nonirradiated thymocytes

A study was made of chromatin endonucleolysis in hypotonic thymocytes incubated in digestive buffers containing different concentrations of potassium, magnesium, calcium, and mercaptoethanol. Inhibition of endonucleolysis by univalent cation during the first 20 min of incubation was followed by intensive chromatin degradation. A decrease in free potassium content retarded chromatin degradation and enhanced the inhibiting effect of the univalent cations. The regularities of changes in the rate of chromatin endonucleolysis in different digestive buffers were similar with both exposed and intact thymocytes.     

Humidity Responses of Stomata and the Potassium Content of Guard Cells

Humidity responses of stomata and changes in the potassium contentof their guard cells were investigated in intact plants anddetached epidermal strips of Valerianella locusta (L.) Betcke.Potassium content was determined by Macallum‘s stain.It was found that changes in stomatal aperture caused by decreasingor increasing humidity were followed only after a delay by changesin the potassium content of the guard cells. By comparison,if stomatal movements occurred in response to changes in illuminationthe relative potassium content of the guard cells correlatedcontinuously with the changes in stomatal aperture. Since thepotassium content of the guard cells changed only after mostof the stomatal movements in response to changes in humiditywere completed changes in potassium content and humidity responsesof stomata can be described as following a hysteresis curve.     

Dependence of ion transport across the plasma membrane on the density of the cell culture. I. Ion flows and the potassium and sodium content in 3 Chinese hamster cell lines (CHO)

Cation transport has been investigated in three lines of Chinese ovary cells CHO-K1 during the cell culture growth. With the increase in the cell density potassium and sodium contents decreased from 1.2 to 0.8-0.5 and from 0.5 to 0.15-0.1 mmole/g protein, respectively. The time courses of potassium and sodium changes were different, and the increase in intracellular K/Na ratio from 1.5-2.0 to 5-10 with the increase in cell density was revealed. The rubidium influx was found to decrease during the culture growth mainly due to the decrease in ouabain-inhibitable and (ouabain + furosemide)- non-inhibitable influxes. The changes in cation fluxes and cation contents were observed in transformed cells without contact inhibition of division and were considered as a manifestation of density-dependent alterations of plasma membrane.     

Seasonal changes in the concentrations of Ca,Fe, K,Mg, Mn and Na in eelgrass (Zostera marina L.) in the Limfjord,Denmark

The seasonal changes in concentrations of calcium, iron, potassium, magnesium, manganese and sodium in above- and below-ground parts of eelgrass (Zostera marina L.) were studied at three locations in the Limfjord, Denmark.The concentrations of calcium, iron and manganese in eelgrass differed significantly at the three stations. Above-ground parts of eelgrass contained significantly higher concentrations of potassium and manganese than below-ground parts, whereas the concentrations of iron and sodium were highest in the below-ground parts. Calcium and mangnesium concentrations in the two fractions were not significantly different.Significant seasonal variations were observed in the concentrations of calcium, potassium, manganese and sodium in above-ground parts of eelgrass and in the concentrations of iron, magnesium and sodium in below-ground parts. Iron, potassium, manganese and, to an extent, sodium showed a similar seasonal pattern with maximum concentrations in the summer and minimum concentrations in the spring or fall, whereas calcium concentrations in the above-ground parts showed the opposite pattern.The observed seasonal variation patterns are discussed in relation to the respective metals and changes in environmental factors.     

Voltage-dependent potassium channels in the molluscan neuron somatic membrane

Under voltage clamp conditions proof of the presence of two populations of potassium current channels was obtained on the molluscan neuron somatic membrane: inactivated and uninactivated. They differ from each other in their physicochemical characteristics, the property of their gating mechanisms, and the molecular structure of their current-conducting part. The inactivated potassium current is largely and selectively inhibited by cooling. Channels of the fast potassium current also are highly sensitive to temperature changes. By using parameters of gating mechanisms of the "fast" potassium channels included in the Hodgkin-Huxley model, the physicochemical properties of channels of this type were described. The density of fixd negative surface charges on the somatic membrane in the region of localization of fast potassium channels was estimated with the aid of the Gouy-Chapman theory. It is 0.3 electron charge/nm². Data on the character of interaction of potassium channels with intracellular sodium ions revealed differences in the structure of the current-conducting part of different types of potassium channels. Experiments on intracellularly perfused molluscan neurons demonstrated the particular features of interaction between intracellular calcium ions and calcium-activated channels under conditions of strictly controlled changes in the intracellular calcium concentration.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 296–307, May–June, 1984.     

Alterations in cation levels and Na-K ATPase activity in rat cerebral cortex during the development of cobalt-induced epilepsy

Abstract— This study was carried out to ascertain what biochemical changes might be present in cobalt-induced epilepsy in the rat. Sodium, potassium, calcium, magnesium, Na-K ATPase activity, water content, protein content and the ability of the tissue to utilize oxygen were measured in (1) the area of the cerebral cortex in which the cobalt was implanted; (2) in an area adjacent to but not including the area of the lesion; and (3) in the homotopic area of the contralateral cerebral cortex. The greatest changes were observed in the area of the lesion itself, with marked increases in calcium, magnesium and sodium contents and decreases in potassium content, Na-K ATPase activity, protein content and the ability of the tissue to utilize oxygen. The only significant findings in the area adjacent to the lesion and in the contralateral cortex were a modest elevation of sodium and a modest decrease in potassium at different time periods after implantation of the cobalt. We feel that the changes observed at the site of cobalt implantation may reflect tissue destruction which is unrelated to the epileptic process.     

Inorganic ion dynamics in the microspore and pollen grain of tobacco during the development of the male gametophyte

We studied the dynamics of mobile potassium, chloride, and nitrate ions during development of the micro-spore and differentiation of the pollen grain in Nicotiana tabacum L. by measuring their concentration in aqueous extracts from cells destroyed by freezing-thawing using ion-selective electrodes. Stage-specific changes in the ion content and intracellular concentration in the male gametophyte were found. A relationship of the dynamics of ions to growth processes and changes in metabolic activity during gametophytogenesis has been discussed. The changes in the potassium and chloride ion concentrations have been interpreted as regulatory changes controlling protein synthesis in the pollen grain vegetative cell.     

Potassium Depletion and Regulation of Angiotensin II Receptors in Vascular Smooth Muscle Cells

Abstract

Mesenteric artery smooth muscle cells were grown in culture media containing high, normal, or low concentrations of potassium to study the effects on angiotensin II (Ang II) receptor regulation. Cell growth was similar among cells grown in the different culture media. Cells grown in high potassium media (K=5.8 mEq/L) had an equilibrium dissociation constant, K_d, of 1.59 ± 0.2 nM, whereas those grown in normal potassium media (K=4.1 mEq/L) had a K_d of 1.79 ± 0.2 nM and those grown in a low potassium media (K=2.9 mEq/L) had a K_d of 1.19 ± 0.12 nM (not significantly different, NS). Binding capacity of smooth muscle cells grown in high potassium media was 81 ± 16.7 fmol/mg prot, 95.1 ± 12.4 fmol/mg prot in those grown in normal potassium media and those grown in low potassium media 86.4 ± 24.1 fmol/mg prot (NS). Binding of radiolabelled Ang II was reduced by approximately 70% in cells exposed to unlabelled Ang II for 30 or 60 minutes. However, this effect of exposure to Ang II to reduce subsequent binding of Ang II was identical in cells grown in high and low potassium medium. Therefore, we were unable to identify a direct effect of low potassium to induce changes in Ang II receptor binding affinity or binding capacity. Previously observed changes in these Ang II binding parameters in potassium-depleted rats was probably a consequence of other factors which were simultaneously altered by potassium deficiency.     

Response of the iron-deficient erythrocyte in the rat to hyperoxia

Normal and iron-deficient rats were exposed to 90% O2 at 760 Torr for 24 or 48 h. Erythrocyte response to hyperoxia was monitored by potassium (rubidium) influx studies, by storage stress, and by ultrastructural studies. Normal rat erythrocytes exhibited morphological changes and decrease of ouabain-sensitive potassium influx compared to unexposed controls. Both components of erythrocyte potassium influx were affected by iron deficiency. Erythrocytes from unexposed iron-deficient rats showed a 50% increase in ouabain-sensitive potassium influx compared to controls. Iron-deficient rats exposed to hyperoxia for 24 or 48 h, had erythrocytes with morphological changes. Erythrocytes of iron-deficient rats exposed for 24 h showed no influx change; those exposed for 48 h showed a decrease of ouabain-sensitive influx compared to erythrocytes of controls.     

Renal regulation of potassium homeostasis in calves in the first week of life including the role of atrial natriuretic peptide

The experiment was carried out on 10 clinically healthy Polish-Friesian var. Black-and-White cow calves, during the first seven days of postnatal life. The results indicate that renal removal of potassium depends primarily on the quantity reabsorbed in the tubules, whereas clearance of the electrolyte, due to stable levels in the blood plasma, depends on the amount excreted in the urine. With stable tubular reabsorption of potassium, a relatively unchanging amount of excreted potassium was observed in the urine. However, reduced tubular reabsorption caused a significant increase in excretion and clearance of the electrolyte. Changes in the amount of filtered potassium play a minor role in the regulation of excretion. Small changes in the blood plasma potassium concentration observed primarily resulted from changes in glomerular filtration rate and tubular reabsorption, since the concentration of electrolyte in the blood after birth remained within the physiological range. The results ofthis study suggest that neonate calf kidneys are sufficiently prepared to regulate kalemia. Atrial natriuretic peptide is not directly involved in the regulation of tubular reabsorption of potassium in calves in the first week of life, although it is highly likely that the peptide is involved in the excretion of potassium in the urine in calves during the first seven days of life.     

Potassium-dependent cambial growth in poplar

To study the involvement of potassium in wood formation, poplar plants ( Populus tremula L. x Populus tremuloides Michx.) were grown over a period of one growing season, under different potassium regimes. Seasonal changes in cambial potassium content, osmotic potential, and cambial activity correlated strongly throughout the season, increasing from spring to summer and decreasing from summer to autumn. Moreover, changing the potassium supply during the growing season affected the seasonal changes of these parameters in a similar way. Low potassium supply markedly reduced cambial activity, the number of expanding cambial cell derivatives, the seasonal rate of radial wood increment, and the vessel frequency. The possible effect of hormones on potassium-dependent cambial growth was investigated and revealed that abscisic acid (ABA) strongly decreased the potassium content within the cambial zone and reduced cambial activity, as well as the number of expanding cambial cell derivatives. In summary, our results indicate a key role for potassium in the regulation of cambial growth and wood formation due to its strong impact on osmoregulation in expanding cambial cells. They also demonstrate involvement of ABA in regulation of potassium-dependent cambial growth.     

Dual effect of L-glutamate on excitatory postjunctional membranes of crayfish muscle

Iontophoretically applied glutamate produces different excitatory postjunctional permeability changes on separate muscle fibers in a single crayfish muslce. At junctions on some fibers glutamate appears to increase the conductance to both sodium and potassium whereas at others its effect is primarily on the sodium conductance. These results obtained by studying the reversal potential for the extracellularly recorded glutamate potential under conditions of varied extracellular sodium and potassium concentrations.     

Dependence of intracellular alkali-ion concentrations of 3T3 and SV 40-3T3 cells on growth density.

Intracellular contents of potassium and of sodium are determined for 3T3 and SV 40-3T3 cells in dependence of growth density. In parallel, total cell volume and volume of intracellular water is determined for these cells suspended in physiological buffer. Intracellular potassium concentration thus evaluated for suspended 3T3 cells exhibits a sharp decrease at cellular growth densities which lead to density dependent inhibition of cell proliferation. In the case of SV 40-3T3 cells, this drop of potassium concentration with increasing cellular growth density is not observed, which correlates well with the absence of cell density dependent inhibition of cell growth in the transformed cell line. These results support the notion that processes of stimulation of quiescent 3T3 cells or of cell density dependent inhibition of their proliferation are mediated by processes including changes of potassium transport characteristics leading to increase or decrease respectively of their intracellular potassium concentration. Furthermore, these and other results suggest, that a difference between normal and transformed cells most relevant to their different proliferation behaviour might reside in different transport characteristics for potassium of the plasma membranes of these cells.     

Age-related changes in the functioning of the mitochondrial potassium-transporting system

Changes in the rate of respiration and functioning of the ATP-dependent potassium channel in liver and heart mitochondria of one-, three-, eight-, and 24-month-old Wistar male rats have been investigated. It was shown that the activity of the channel in the mitochondria of both tissues in 24-month-old animals decreases more than three times, and the content of potassium, 1.5–2 times compared with young one-month-old rats. The changes occur against the background of age-related decrease of energy supply in mitochondria, the respiratory complex-I undergoing the greatest changes upon aging. The decrease of channel activity may be the result of changes in channel sensitivity to modulators and a decrease in the expression of mitochondrial K+-transporting channel-protein with a molecular mass of 5.5 kDa upon aging found in this work. As a result, the functioning of not only the mitoK_ATP but also the whole mitochondrial potassium cycle is impaired.     

Effects of potassium,sodium, and azide on the ionic movements that accompany activity in frog nerves

Stimulation of intact or desheathed frog sciatic nerves produced an increase in the sodium content and a decrease in the potassium content of this tissue. In desheathed preparations the magnitudes of the changes in ionic contents decreased as the concentration of the potassium in the bathing solution was increased, while changing the external sodium concentration produced small effects on the ionic shifts. During tetanization, the rate of decline of the compound action potential also decreased as the external potassium concentration increased. Eliminating the activity respiration with 0.2 mM azide did not greatly modify the changes in sodium and potassium distribution that accompanied activity in either intact or desheathed nerves.     

Comparative measurements of potassium and chloride with ion-sensitive microelectrodes and x-ray microanalysis in cultured skeletal muscle fibers

Summary Data of the intracellular electrolyte concentration of potassium and chloride in cultured muscle cells measured by x-ray analysis were compared by using the different activity coefficients with intracellular potassium and chloride activities measured with double-barrelled microelectrodes. By using an activity coefficient of 0.6, 95% of the potassium microelectrode measurements are in accordance with the x-ray analysis values, in spite of a scattering of the values. Membrane potential and intracellular potassium values are linearly related. x-ray analysis and ion-sensitive microelectrodes measured the cytoplasmic chloride in the same range. Taking into account known activity coefficients, an error of 25% must be assumed with the intracellular chloride measurements. However, x-ray analysis and ion-sensitive microelectrode investigations are reliable tools to study intracellular potassium and chloride changes, which play an important role in membrane characteristics.     

Potassium homeostasis influences the locomotion and encystment of zoospores of plant pathogenic oomycetes

Zoospores of plant pathogenic oomycetes exhibit distinct swimming speeds and patterns under natural conditions. Zoospore swimming is influenced by ion homeostasis and changes in the ionic composition of media. Therefore, we used video microscopy to investigate swimming patterns of five oomycete species in response to changes in potassium homeostasis. In general, zoospore speed tended to be negatively correlated with zoospore size. Three Phytophthora species (Phytophthora palmivora, Phytophthora megakarya, and Phytophthora infestans) swam in straight patterns with speeds ranging from 50 to 250 microm/s whereas two Pythium species (Pythium aphanidermatum and Pythium dissotocum) swam at similar speeds ranging from 180 to 225 microm/s with a pronounced helical trajectory and varying amplitudes. High external concentrations of potassium salts reduced the swimming speed of Ph. palmivora and induced encystment. This was not observed for Py. aphanidermatum. Application of the potassium ionophores gramicidin, nigericin and valinomycin resulted in reduced swimming speeds and changes in the swimming patterns of the Phytophthora species. Therefore, potassium ions play a key role in regulating zoospore behavior.