Na+ and K+ concentrations and the regulation of protein synthesis in Sindbis virus-infected chick cells

Interaction of delta-9-tetrahydrocannabinol with rat B103 neuroblastoma cells

The effect of delta-9-tetrahydrocannabinol (delta-9-THC) on the growth kinetics and morphology of rat B103 neuroblastoma cells was assessed. Delta-9-THC in doses ranging from 10(-4) to 10(-7) M inhibited cellular growth in a dose-dependent fashion as evidenced by delay in doubling time, decrease in saturation density, and decrease in efficiency of plating. The inhibition in cellular growth was paralleled by dose-related alterations in cell morphology. Modifications included rounding of cells, retraction of neurites, blebbing of the cell surface, and exfoliation of the plasma membrane. Cytoplasmic alterations included distension of the endoplasmic reticulum, Golgi apparatus, and perinuclear space, and macrovacuolization. Intracytoplasmic laminated inclusions and vesicular clusters were suggestive of membrane repair in drug-treated cells. These morphological changes were accompanied by cytoskeletal rearrangement in the absence of significant alteration in the concentration of total cytoskeletal protein. Autoradiographic examination of the intracellular fate of 3H-delta-9-THC demonstrated that the drug was confined to the cytoplasmic compartment and often associated with macrovacuoles. These results suggest that delta-9-THC interacts with cellular membranes, thereby altering neuroblastoma cell growth and behavior.

Sodium ion influx in proliferating lymphocytes: an early component of the mitogenic signal

Stimulation of pig peripheral blood lymphocytes with concanavalin A (Con A) provoked a rapid increase (two- to threefold) in the rate of ouabain-inhibitable K+ uptake observable within 3-10 min of stimulation with mitogen. At least two phases can be distinguished in the activation of the Na+/K+ pump: the early phase (till 3 h) is characterized by an unaltered number of ouabain binding sites and the later phase (noted at 5 h) by an increased number of such sites. Both K+ efflux and influx increased to the same extent, thereby maintaining [K+]i at the same level as in resting cells (120 mM). Within 3 min of addition of mitogen, the rates of total and amiloride-inhibitable Na+ uptake went up two- and fourfold, respectively, thus resulting in rapid increase in [Na+]i from 20 to about 50 mM. Activation of the Na+/K+ pump was not observed when the cells were stimulated with Con A in low Na+ medium (9 mM), nor did the usual rise in [Na+]i occur. When monensin (30 microM), a Na+/H+ ionophore, was added to resting cells, an increase in both [Na+]i and active K+ uptake occurred in normal medium but not when cells were suspended in low Na+ isotonic buffer. Amiloride (500 microM), on the other hand, prevented both the Con A-induced increase in [Na+]i and the activation of the Na+/K+ pump. Despite complete inhibition of the Na+,K+-ATPase in the presence of ouabain (1 mM), Con A activated the amiloride-inhibitable Na+ uptake in the usual way. In mouse splenocytes stimulated with Con A, there was also a parallel rise in both [Na+]i and active K+ uptake but this took considerably longer to occur than was the case in pig peripheral blood lymphocytes. Increase in both ionic fluxes, the former passive and the latter active, is essential to the entry and maintenance of the cells in proliferative cycle.

Increased sensitivity of virus-infected cells to inhibitors of protein synthesis does not correlate with changes in plasma membrane permeability

Semliki Forest virus-infected BHK cells or herpes simplex virus-infected Vero cells were incubated with the protein synthesis inhibitors hygromycin B and gougerotin. Infected cells take up no more [3H]hygromycin or [3H]gougerotin than do mock-infected cells, at a time p.i. at which either compound is more inhibitory to protein synthesis in infected, than in mock-infected cells. The concentrations of hygromycin and gougerotin required to inhibit protein synthesis in intact cells (irrespective of whether they are infected or not) are several orders of magnitude higher than those required in either permeabilized cells or in cell-free systems. Infected cells take up 86Rb+ at the same rate as mock-infected cells, their intracellular content of K+ is the same, and the activity of the Na+ pump is the same. It is concluded that the increased efficacy of hygromycin and gougerotin in virus-infected cells is a consequence of altered intracellular compartmentation and that increases in permeability of the plasma membrane, if any, are so small as to be undetectable by direct methods.

Cell killing by ultraviolet-inactivated human immunodeficiency virus

Extensive cell killing and cytopathology were observed within 24 hr after exposure of a clonal cell line of human T-4 lymphocytes (RH9) to culture supernatants containing human immunodeficiency virus (HIV). Ultraviolet-irradiated HIV-containing culture fluids were also capable of killing RH9 cells and of inducing specific cytopathic effects which were indistinguishable from those induced by unirradiated virus-containing preparations. The uv-irradiated HIV was incapable of forming proviral DNA using the endogenous virion genomic RNA as a template. The RH9 cells persistently infected with HIV did not release soluble cytotoxic factors to account for the cell killing observed when culture supernatants were added to uninfected RH9 cells. The fraction involved in cell killing had the hydrodynamic properties of a retrovirus. These results suggest that a virion component is responsible for cell killing by HIV.

Interferon production in L929 cells under impaired translational conditions: comparison of rates of interferon, actin, Newcastle disease and encephalomyocarditis viruses mRNAs initiation of protein synthesis

The pattern of Interferon (IFN) production in virus-infected cells has been compared with the rate of bulk cellular protein synthesis, on one hand, and with the synthesis of representative cell and virus proteins such as actin, the gamma and the NP proteins of encephalomyocarditis (EMC) and Newcastle Disease (NDV) viruses, on the other hand. This was investigated under conditions of impaired protein synthesis such as i) high osmolarity media, ii) a virus-induced shut-off, and iii) in cells exposed to relatively low doses of cycloheximide (CXM), which slow elongation of protein chain and thus favour the translation of low-affinity messenger RNAs (mRNAs). In each instance IFN production was compared with 35S-methionine incorporation into TCA-precipitable materials and into SDS-polyacrylamide gel-analysed proteins. Data obtained from each of the experimental approaches all indicate that IFN production and cellular protein synthesis are modified in a closely related fashion suggesting that their mRNAs share a similar degree of affinity for ribosomes. Conversely, two mRNAs coding for representative EMC and NDV virus proteins exhibit, respectively, the highest and the lowest affinity for ribosomes as compared to actin mRNA.

Studies on final differentiation of rat renal proximal tubular cells in culture

The ontogeny of effective Na and K permeability has been studied in renal epithelial cells isolated from the outermost superficial cortex from adult and young (10-15 days) rats. The cells were cultured for 2-4 days and exhibited phloridzin-inhibitable alpha-methylglucoside uptake, characteristic of renal proximal tubular cells (RPTC). Intracellular concentrations of K, Na, Cl, and P and kinetics of changes in intracellular ionic content after inhibition of Na-K-ATPase with 1 mM ouabain (or by incubation in low-K medium) were measured in individual cells using electron probe analysis. Intracellular concentrations of K, Na, Cl, and P were equivalent in young and adult rat RPTC. Adult rat and young rat cells preincubated in K-free medium rapidly recovered normal intracellular K and Na contents when returned to 5.5 mM K medium. The recovery was almost immediately blocked by ouabain. Effective permeabilities measured as half time of K efflux and Na influx after ouabain inhibition of Na-K-ATPase were higher in adult than in young RPTC cultured for less than 4 days. Effective K and Na permeabilities decreased significantly with increasing time in culture in adult but not in young rat RPTC. Among young rat RPTC, half times of Na and K fluxes were significantly correlated to age. Effective K and Na permeabilities were lower in both young and adult rat RPTC that had been serum deprived for 24 h than in cells that had been continuously cultured in serum. In cells cultured for 3 days and serum deprived for 1 day, the addition of serum significantly increased K and Na permeability both in young and adult RPTC, but the effect was more pronounced in young RPTC where permeability reached the same high values as in adult RPTC continuously cultured in serum. In conclusion, effective Na and K permeabilities and serum activation of "permeability units" change during ontogeny. These ontogenic changes might be blunted after a few days in culture due to dedifferentiation of adult rat RPTC.

Heat-inactivated frog virus 3 selectively inhibits equine herpesvirus type 1 translation in a temporal class-dependent manner

Superinfection of equine herpesvirus type 1 (EHV-1)-infected rabbit kidney cells with heat-inactivated frog virus 3 (delta FV3) differentially blocked EHV-1 protein synthesis. The extent of inhibition varied with the specific EHV-1 message, but in general late protein synthesis was inhibited more than early and immediate early translation. Since FV3 has been shown to block heterologous RNA and protein synthesis, it was necessary to determine whether the observed reduction in herpesvirus protein synthesis was primarily due to a block in translation or to an earlier inhibition of EHV-1 mRNA synthesis. To distinguish between these alternatives, replicate cultures of EHV-1 infected cells were either superinfected with delta FV3 or treated with 10 micrograms/ml actinomycin D at 6 hr after infection, and EHV-1 protein synthesis monitored 3 hr later. We found that addition of actinomycin D to EHV-1 infected cultures had only a slight effect on EHV-1 translation, whereas superinfection with delta FV3 markedly reduced EHV-1 protein synthesis. This result suggested that the observed decline in EHV-1 protein synthesis was not due to the inhibition of herpesvirus mRNA synthesis. In addition, we showed that RNA extracted from delta FV3-superinfected cells directed the synthesis of full-size EHV-1 proteins in vitro indicating that shut-off was not caused by the degradation of EHV-1 mRNAs. Taken together these results show that delta FV3 selectively inhibited EHV-1 protein synthesis and are consistent with earlier observations which suggest that translational shut-off occurs at initiation.

Adaptive response of cultured fibroblasts to hyperosmolarity

Raising to 0.4 osM the osmolarity of the medium in which chick embryo fibroblasts are incubated quickly increases the internal Na+ concentration, inhibits protein synthesis and also stimulates amino acid transport. On extending the incubation time, cells appear to adapt to the altered environment, as the Na+ content declines toward control values within few hours. Protein synthesis resumes its normal rate within 12-14 h of treatment. Experimental alteration of the monovalent cation content by substituting extracellular Na+ with other osmolites or by using ouabain or the ionophore monensin reveals an impairment of protein synthesis. Analysis by SDS-PAGE reveals an alteration of the polypeptide pattern expressed by hyperosmolarity-exposed cells, resulting in an enhanced synthesis of the 87, 75 and 53 kD proteins and inhibition of a 125 kD band. The previously increased amino acid transport activity also reverts to its normal level, but only after 40-50 h of incubation. The growth rate of these cells does not appear to be significantly affected during the first 3 days of the hyperosmolar treatment. Results presented in this publication identify the alteration of the protein synthesis rate, the change in the intracellular cation content and the increase in amino acid transport activity as plausible parameters of adaptive response, and suggest that the modulation of gene expression observed in cells exposed continuously to hyperosmolarity may be a consequence of the alteration of the intracellular monovalent cation concentration.

Intracellular K+ and the expression of transformation parameters by chick cells transformed with the Bryan strain of Rous sarcoma virus

As normal chick embryo (CE) cells entered quiescence the intracellular concentrations of both Na+ and K+ declined. Comparable decreases in intracellular concentrations of Na+ and K+ were not observed in CE cells transformed by either the Schmidt-Ruppin (SR) or the Bryan (B) strain of Rous sarcoma virus (RSV). Intracellular concentrations of Na+ were higher in SR-RSV-transformed CE cells than in B-RSV-transformed cells and uninfected CE cells at all times after plating. In contrast, intracellular concentrations of K+ were higher in B-RSV-transformed CE cells than in SR-RSV-transformed cells. Uninfected CE cells incubated in medium containing an elevated concentration of K+ (an increase from 5 to 30 mM) exhibited several, but not all, of the transformation parameters expressed by B-RSV-transformed CE cells.

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Effect of medium hypertonicity on reovirus translation rates. An application of kinetic modeling in vivo

Translation rates were determined for host and virus mRNAs in reovirus-infected SC-1 cells in hypertonic medium. The effect of low doses of cycloheximide on these translation rates was also measured. The results show that hypertonicity selectively stimulates viral translation relative to host translation. Moreover, in hypertonic medium, host translation is slightly stimulated by low doses of cycloheximide, whereas viral translation is markedly inhibited. This effect of cycloheximide is precisely the opposite to what was previously observed in isotonic media [Walden, W. E., Godefroy-Colburn, T., & Thach, R. E. (1981) J. Biol. Chem. 256, 11739-11746]. It is shown that both these effects of hypertonicity are predicted by the message competition/discrimination model previously described and thus provide support for the applicability of certain aspects of the model to translation rates in vivo.

Modification of membrane permeability during Semliki Forest virus infection

Modification of membrane permeability has been analyzed in Semliki Forest virus (SFV)-infected cells by means of translation inhibitors not permeable to normal cells. A higher inhibition of protein synthesis in the infected cells is only observed with those antibiotics that do not easily pass the cell membrane, but not with others, permeable to cells, such as anisomycin, cycloheximide, trichodermin, etc. It does not, therefore, seem that the suggestion of M. A. Gray, K. J. Micklem, and C. A. Pasternak [Eur. J. Biochem. 135, 299-302, (1983)] that protein synthesis in virus-infected cells is more susceptible to translation inhibitors in general is correct. Both low- and high-molecular weight compounds enter the cell very early during SFV infection. This permeabilization is blocked by compounds known to increase the pH of coated vesicles, such as NH4Cl and chloroquine. Inhibition of energy production by means of N3Na and 2'-deoxyglucose also blocks this process. The optimal external pH for this early permeabilization is around 7-8. Acidic pH inhibits the entry of these impermeant antibiotics promoted by SFV. Analysis of 86Rb+ content in SFV-infected HeLa cells also indicates that a drastic decline in this cation takes place, in agreement with previous findings, but disagreeing with the previous results. A parallel between the decrease in this cation and the blockade of protein synthesis is apparent, throughout the course of infection. In addition to the early permeabilization that takes place during virus entry, increased entry of hygromycin B and alpha-sarcin also occurs in SFV-infected cells from 2 to 3 hr postinfection, but not when late viral replication is blocked by means of interferon treatment.

Effect of tunicamycin on the development of the cytopathic effect in Sindbis virus-infected avian fibroblasts

In Sindbis virus-infected avian cells the development of the cytopathic effect is correlated with the disruption of plasma membrane function. Sindbis virus inhibits the activity of the Na+K+ATPase, a membrane-associated enzyme complex which regulates intracellular monovalent cation levels. Tunicamycin, which blocks envelope protein glycosylation, prevents inhibition of Na+K+ATPase activity and the development of morphological changes in Sindbis virus-infected cells. Although inhibition of Na+K+ATPase activity is not essential for the termination of host protein synthesis, membrane-mediated events may favor the selective translation of viral proteins. The termination of host protein synthesis does not contribute to the development of these cytopathic changes in the time frame examined. In tunicamycin-treated, Sindbis virus-infected cells, unglycosylated E1 is inserted into the plasma membrane but virus release is prevented. In productively infected cells, therefore, the inhibition of Na+K+ATPase activity and the development of the cytopathic effect may result from terminal events in virus assembly and/or virus release.

Alterations of 86Rb+ fluxes in poliovirus-infected HeLa cells and their dependence on virus replication

Components of the 86Rb+ influx were investigated subsequent to poliovirus infection in the presence and absence of guanidine-HCl, both under normal steady-state conditions and after Na+ preloading of the cells. Measurements of the ouabain-sensitive 86Rb+ uptake indicated a biphasic change in the activity of the Na+, K+ pump in the course of virus infection: a transient increase in the second hour postinfection, that was detectable only after Na+ preloading and inhibition after 3 hr. The enhanced activity of the Na+, K+ pump was not affected, while the decrease later was fully prevented by the antiviral agent guanidine-HCl. The piretanide-sensitive 86Rb+ uptake due to the Na+, K+, 2 Cl- cotransport system also became strongly inhibited beginning in the second hour postinfection. The inhibition of this transport system was partially antagonized by guanidine-HCl. The remaining 86Rb+ influx in the presence of ouabain and piretanide increased in the third hour postinfection. The latter change in 86Rb+ influx, indicating an increased permeability to monovalent cations was completely abolished by guanidine-HCl.

Alterations in monovalent cation transport in Sindbis virus-infected chick cells

Influx experiments using the potassium tracer 86Rb+ indicated that the activity of the Na+K+ ATPase, or sodium pump, was reduced 40-50% as a consequence of Sindbis virus infection of avian fibroblasts. The inhibition of this ouabain-sensitive, active transport system temporally correlated with a decrease in the intracellular K+ concentration and the termination of cellular protein synthesis. By contrast, the rate of influx facilitated by the furosemide-sensitive (Na+K+Cl-) cotransport system was only slightly depressed. Efflux experiments indicated that no alterations in the relative rate of nonspecific permeability or "leakage" of K+ could be detected in chick cells infected by Sindbis virus. The amount of [3H]ouabain bound to Sindbis virus-infected cells paralleled the reduction in Na+K+ ATPase activity. These binding studies revealed no difference in the number of Na+ pump sites. The Km of ouabain binding, however, increased approximately 3.5-fold in the virus-infected cells. No change in the apparent affinity of the Na+ pump for K+ could be detected, yet the Vmax for ouabain-sensitive K+ transport was decreased. These experiments suggest that a reduction in Na+K+ ATPase turnover results in the altered intracellular monovalent cation levels found in Sindbis virus-infected chick cells.

Modulation of production of hepatitis B surface antigen by a human hepatoma cell line

Three drugs were assayed for their capacity to inhibit hepatitis B surface antigen (HBsAg) production by the PLC/PRF/5 human hepatoma cell line. The effect on cell growth and HBsAg production of Cordycepin, 6-azauridine, and Hygromicin B is reported. Hygromicin B, a translation inhibitor unable to penetrate normal cells, greatly reduced HBsAg production by growing and confluent cells.

Action of oligomycin on cultured mammalian cells. Permeabilization to translation inhibitors

Oligomycin, an inhibitor of ATP synthesis, has been used as a model to study the effects of ATP depletion on macromolecular synthesis and modification of membrane permeability. Protein synthesis is totally blocked by the antibiotic, whereas RNA and DNA synthesis are less inhibited. Different concentrations of monovalent and divalent cations do not revert the inhibition of protein synthesis. Measurement of cellular ATP and 86Rb+ content indicate that the blockade of translation depends on the ATP content. A significant decrease in cellular ATP does not lead to the reduction of monovalent ions in the cell, although hyperpolarization of the cell membrane does take place. An increased membrane permeability to some inhibitors develops when the cells are hyperpolarized by oligomycin.

Ribosome topography in baby hamster kidney cells infected with Sindbis and vesicular stomatitis viruses

The topography of polysomal ribosomes in mock-infected and in Sindbis virus- and vesicular stomatitis virus-infected BHK cells was investigated using a double, radioactive labelling technique. Ribosomal proteins in intact polysomes were surface labelled by reductive methylation using [14C]formaldehyde. Following removal of ribosomal RNA, proteins were denatured in 6 M guanidine and labelled with [3H]borohydride. Labelled ribosomal proteins were separated by electrophoresis in two-dimensional gels and the 3H/14C ratio for each ribosomal protein was taken as an index of its relative surface exposure in intact ribosomes. Comparison of the ratios for individual ribosomal proteins in Sindbis virus-infected vs. control polysomes indicated that proteins L7, L8, L17, L26 and S19 became more 'buried' and others such as L4, L29, L36, S2 and S26 became more 'exposed' in infected cells. Most of the topographical alterations occurred in the large ribosomal subunit. In contrast, infection of BHK cells with vesicular stomatitis virus induced little or no topographical alteration.

Protein synthesis in cells infected with Semliki Forest virus is not controlled by intracellular cation changes

Treatment of BHK cells with 1 microM nigericin results in a 55% decrease in K+ and a 3.3-fold increase in intracellular Na+; protein synthesis under these conditions is depressed by 35%. In BHK cells infected with Semliki Forest virus (SFV), protein synthesis is depressed by 76% 6.5 h after infection; intracellular K+ is unchanged, and intracellular Na+ is increased 1.8-fold at this time. These results suggest that the increase in intracellular Na+ in SFV-infected BHK cells does not adequately account for the decrease in protein synthesis, and makes it likely that an increased Na+ concentration is a consequence, not a cause, of alterations in protein synthesis in virally-infected cells. No evidence was obtained for the purported [Alonso, M. A. and Carrasco, L. (1980) Eur. J. Biochem. 109, 535-540; (1981) Eur. J. Biochem. 118, 289-294; (1981) FEBS Lett. 127, 112-114] ability of 1 microM nigericin to permeabilize' cells.

Induction of stress proteins in Sindbis virus- and vesicular stomatitis virus-infected cells

Two proteins which are related to certain proteins induced by hyperthermia (heat shock proteins; hsp) are synthesized during lytic infection of chick embryo (CE) cells by Sindbis virus or vesicular stomatitis virus (VSV). Incubation of the infected cells at elevated temperature further increased the rate of synthesis of these proteins. The stress proteins induced by Sindbis virus had different mobilities on SDS-polyacrylamide gels compared to related stress proteins induced in mock-infected CE cells. Induction of the stress proteins in Sindbis virus- and VSV-infected CE cells was actinomycin D sensitive. Kinetic studies indicated that induction of the stress proteins is an early event during infection. The lytic virus-induced selective termination of host protein synthesis did not affect the synthesis of these proteins. Furthermore, the synthesis of these virus-induced stress proteins was resistant, relative to the synthesis of most host proteins, to alterations in the intracellular concentrations of Na+ and K+. The synthesis of a protein related to a major low-molecular-weight hsp of CE cells was not induced after Sindbis virus or VSV infection. Immunoprecipitation experiments and sedimentation analyses demonstrated that significant levels of the capsid protein (C) of Sindbis virus and nucleocapsid protein (N) of VSV are physically associated with a hsp in lysates of infected CE cells.

Effect of high salt treatment on influenza B viral protein synthesis in MDCK cells

Based on the information that high salt inhibits the initiation of cellular mRNA translation which depends on the function of the 5'-terminal structure of mRNA, we compared the effect of high salt on translation of host cellular mRNAs and influenza viral mRNAs, both of which are of 5'-terminal structure. Brief exposure of influenza B virus-infected MDCK cells to high salt medium resulted in a dose-dependent inhibition of viral polypeptide synthesis as well as of cellular polypeptide synthesis, but it had less effect on synthesis of viral polypeptides, particularly nonstructural protein (NS). Under these conditions the Na+ content of the infected cells was significantly increased. A similar salt effect on in vitro translation of viral and cellular mRNAs extracted from infected cells was also observed. There was no significant difference in sensitivity to hypertonic block of in vivo translation of influenza viral mRNAs and vesicular stomatitis virus mRNAs, the latter of which possess a virus-directed structure at the 5'-terminus.

Myxoviruses do not induce non-specific alterations in membrane permeability early on in infection

The permeability characteristics of cells infected with myxoviruses have been studied by measuring the concentrative uptake of nutrients, the concentration of intracellular K+, and the maintenance of the Na+ gradient across the plasma membrane. Cells either show no change at all (Sendai virus-infected BHK cells and measles virus-infected Vero cells) or they show a decreased ability to concentrate nutrients, while intracellular K+ and the Na+ gradient remain unchanged (Sendai and influenza virus-infected L-1210 cells, measles virus-infected lymphocytes and mumps virus-infected L-41 cells). In no case, therefore, was a change observed that resembles the non-specific increase in membrane permeability induced by haemolytic paramyxoviruses (35, 42) or the non-specific membrane leakiness postulated to take place in infected cells (8, 9). A preliminary account of some of these findings has been presented (39).

Poliovirus-induced alterations in HeLa cell membrane functions

Protein synthesis, amino acid uptake, membrane potential, cell volume, Na+ and K+ levels, and ATPase (Na+,K+ activated; EC 3.6.1.3) activity were investigated in control and poliovirus-infected HeLa cells. Inhibition of protein synthesis was first observed 60 min postinfection and reached a maximum at 120 min. The onset of protein synthesis inhibition coincided with a decrease in cell volume and with an elevation of ATPase activity in isolated HeLa cell membranes. Some 3 h after virus adsorption, ATPase activity was inhibited, the Na+-K+ gradient of the cell collapsed, both membrane potential-dependent tetraphenylphosphonium ion uptake and amino acid uptake were reduced, and the cell volume increased. These results provide further experimental support for the hypothesis that modification of the cell membrane plays an important role in the strategy of cytopathogenic viruses in the shutoff of host metabolism and cell death.

A survey of intracellular Na+ and K+ of various normal, transformed, and tumor cells

Intracellular concentrations of Na+ and K+ of various normal, transformed, and tumor cell cultures were analyzed by atomic absorption spectrophotometry. In all of the cultures analyzed there were markedly different concentrations in the transformed and tumor cells when compared to their normal counterparts. Although increased Na+ was often observed, there were no definitive correlations between absolute ion concentrations, or Na+:K+ ratios, and cell transformation.

Membrane-mediated alterations of intracellular Na+ and K+ in lytic-virus-infected and retrovirus-transformed cells

Infection of chick-embryo fibroblasts and other cells by certain animal viruses results in alterations in the intracellular concentrations of Na+ and K+. Dramatic alterations in monovalent-cation concentrations of lytic-virus-infected cells may favor the synthesis of viral proteins over cellular proteins. More subtle alterations in retrovirus-transformed cells may result in the expression of many morphological and biochemical changes associated with the transformed phenotype.

Virally induced alterations in cellular permeability: a basis of cellular and physiological damage?

Virally induced permeability changes occur when haemolytic paramyxoviruses are added to cells; similar (though not identical) changes take place during infection of cells with viruses from several families (including paramyxoviruses). These changes occur in intact, viable cells, and precede subsequent cytopathic effects, to which they are likely to contribute. There is accumulating evidence to suggest that virally induced permeability changes may also underlie the physiological and clinical consequences of viral infection in certain situations.

Reversion by hypotonic medium of the shutoff of protein synthesis induced by encephalomyocarditis virus

Infection of human HeLa cells by picornaviruses produces a drastic inhibition of host protein synthesis. Treatment of encephalomyocarditis virus-infected HeLa cells with hypotonic medium reversed this inhibition; no viral protein synthesis was detected. The blockade of viral translation by hypotonic conditions was observed for a wide range of multiplicities of infection. However, only with low virus-to-cell ratios did cellular protein synthesis resume. The ratio of cellular to viral mRNA translation was strongly influenced by the concentration of monovalent ions present in the culture medium: a high concentration of NaCl or KCl favored the translation of viral mRNA and strongly inhibited cellular protein synthesis, whereas the opposite was true when NaCl was omitted from the culture medium. Once viral protein synthesis had been blocked by hypotonic medium treatment, it resumed when the infected cells were placed in a normal or hypertonic medium, indicating that the viral components synthesized in the infected cells were not destroyed by this treatment. These observations reinforced the idea that ions play a role in discriminating between viral and cellular mRNA translation in virus-infected animal cells.

Monovalent cation metabolism and cytopathic effects of poliovirus-infected HeLa cells

To better understand the significance of 22Na+ accumulation by poliovirus-infected HeLa cells (C. N. Nair, J. W. Stowers, and B. Singfield, J. Virol. 31:184, 1979), measurements of cellular Na+, K+, and Cl- contents, volume, and density were carried out at intervals after infection. In addition, the rates of 22Na+ washout from infected and control cells were determined. Starting at around 3 h postinfection, the Na+ content of infected cells increased, whereas the K+ content decreased progressively, resulting in a net loss in the monovalent cation content decreased progressively, resulting in a net loss in the monovalent cation content per cell. The loss in cellular chloride content exceeded that in monovalent cation content. The kinetics of 22Na+ washout from infected and control cells revealed the presence of an extra Na+ compartment in infected cells. A net loss in the monovalent cation activity of infected cells was indicated by the loss of cell water as reflected in a decrease in cell volume and an increase in cell density. In spite of a net loss in monovalent cation content per cell, Na+ accumulation coupled with cell shrinkage resulted in substantial increases in the concentrations of not only Na+ but also K+. The results suggested a possible role for tonicity change in the morphological lesions of poliovirus cytotoxicity.