Protein Expression in the Gastrocnemius Muscle of a Rodent Shrapnel-Injury Model

With shrapnel injuries, the metal fragment is usually left in place to reduce the risk of morbidity extensive surgery might bring. This means the individual may retain those metals for the remainder of their life. Often the long-term health effects of the embedded metal are not known, especially with respect to protein damage and perturbations of muscle repair pathways. In this study, using homogenates of rat gastrocnemius muscle implanted with pellets of military-relevant metals, we investigated expression of iNOS and eNOS, enzymes involved in nitric oxide production, as well as MMP-2 and MMP-9, matrix metalloproteinases associated with muscle repair. In addition, hydroxynonenal-modified proteins were investigated to assess metal-induced oxidative damage and metal levels in the gastrocnemius determined. Metals were implanted for up to 12 months in order to determine the long-term effects on the expression of muscle-associated proteins. With the exception of iron and cobalt at 1-month post-implantation, there were no significant differences in metal levels in the gastrocnemius in any of the cohorts. Protein expression analysis showed significant decreases in iNOS and eNOS in the 6-month and 12-month lead and depleted uranium groups. Hydroxynonenal-modified proteins were also significantly increased in the iron, copper, lead, and depleted uranium groups. These results suggest that some embedded metals can induce long-term oxidative damage, as well as affect enzyme systems involved in signal transduction.

Urine miRNAs as potential biomarkers for systemic reactions induced by exposure to embedded metal

Aim: Explore the potential of urine microRNAs as biomarkers that may reflect the biological responses to pure metals embedded in skeletal muscle over time. Materials & methods: We tested a panel of military-relevant metals embedded in the gastrocnemius muscles of 3-month-old, male, Sprague-Dawley rats (n = 8/group) for a duration of 1, 3, 6 and 12 months, and performed small RNA-sequencing on the urine samples. Results: Results provide potential tissue targets affected by metal exposure and a list of unique or common urine microRNA biomarkers indicative of exposure to various metals, highlighting a complex systemic response. Conclusion: We have identified a panel of miRNAs as potential urine biomarkers to reflect the complex systemic response to embedded metal exposure.

In vitro model of perimenopausal depression implicates steroid metabolic and proinflammatory genes

The estimated 20-30% of women who develop perimenopausal depression (PMD) are at an increased risk of cardiovascular and all-cause mortality. The therapeutic benefits of estradiol (E2) and symptom-provoking effects of E2-withdrawal (E2-WD) suggest that a greater sensitivity to changes in E2 at the cellular level contribute to PMD. We developed an in vitro model of PMD with lymphoblastoid cell lines (LCLs) derived from participants of a prior E2-WD clinical study. LCLs from women with past PMD (n = 8) or control women (n = 9) were cultured in three experimental conditions: at vehicle baseline, during E2 treatment, and following E2-WD. Transcriptome analysis revealed significant differences in transcript expression in PMD in all experimental conditions, and significant overlap in genes that were changed in PMD regardless of experimental condition. Of these, chemokine CXCL10, previously linked to cardiovascular disease, was upregulated in women with PMD, but most so after E2-WD (p < 1.55 × 10^-5). CYP7B1, an enzyme intrinsic to DHEA metabolism, was upregulated in PMD across experimental conditions (F_(1,45) = 19.93, p < 0.0001). These transcripts were further validated via qRT-PCR. Gene networks dysregulated in PMD included inflammatory response, early/late E2-response, and cholesterol homeostasis. Our results provide evidence that differential behavioral responsivity to E2-WD in PMD reflects intrinsic differences in cellular gene expression. Genes such as CXCL10, CYP7B1, and corresponding proinflammatory and steroid biosynthetic gene networks, may represent biomarkers and molecular targets for intervention in PMD. Finally, this in vitro model allows for future investigations into the mechanisms of genes and gene networks involved in the vulnerability to, and consequences of, PMD.

Spectroscopic and Spectrometric Approaches for Assessing the Composition of Embedded Metals in Tissues

Many medical devices contain metals that interface with the body. Additionally, embedded metal fragments from military wounds are typically not removed, to avoid the risk of morbidity associated with invasive surgery. The long-term health consequences of many of these materials are not thoroughly understood. To this end, we have exposed rats for up to one year to implanted single-element metal pellets of any one of Al, Co, Cu, Fe, Ni, Pb, Ta, or W. Various tissues were harvested and flash frozen for analysis of their metal distribution. We discuss approaches to most thoroughly and reliably evaluate the distribution of metal in these tissues. The path to the most appropriate analytical technique took us through extensive examination of the tissues using scanning electron microscopy with energy dispersive X-ray spectroscopy (XPS), X-ray photoelectron spectroscopy (XPS), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Though any one of these methods is highly relied upon in surface chemistry analysis, LA-ICP-MS alone showed presence of metal in the tissue. This information will help build robust methods to bridge the gap in our understanding of biosolubility and distribution of embedded metal throughout the body.

Effect of embedded metal fragments on urinary metal levels and kidney biomarkers in the Sprague-Dawley rat

BACKGROUND

Wounds with embedded metal fragments are an unfortunate consequence of armed conflicts. In many cases the exact identity of the metal(s) and their long-term health effects, especially on the kidney, are not known.

AIM OF STUDY

The aim of this study was to quantitate the urinary levels of metals solubilized from surgically implanted metal pellets and to assess the effect of these metals on the kidney using a battery of biomarker assays.

MATERIALS AND METHODS

Using a rodent model system developed in our Institute to simulate embedded fragment injuries, eight metals considered likely components of an embedded fragment wound were individually implanted into the gastrocnemius muscle of male Sprague-Dawley rats. The rats were followed for 12 months post-implantation with urine collected prior to surgery then at 1-, 3-, 6-, 9-, and 12-months post-implantation to provide a within-subjects cohort for examination. Urinary metal levels were determined using inductively coupled plasma-mass spectrometry and urinary biomarkers assessed using commercially available kits to determine metal-induced kidney effects.

RESULTS

With few exceptions, most of the implanted metals rapidly solubilized and were found in the urine at significantly higher levels than in control animals as early as 1-month post-implantation. Surprisingly, many of the biomarkers measured were decreased compared to control at 1-month post-implantation before returning to normal at the later time points. However, two metals, iron and depleted uranium, showed increased levels of several markers at later time points, yet these levels also returned to normal as time progressed.

CONCLUSION

This study showed that metal pellets surgically implanted into the leg muscle of Sprague-Dawley rats rapidly solubilized with significant levels of the implanted metal found in the urine. Although kidney biomarker results were inconsistent, the changes observed along with the relatively low amounts of metal implanted, suggest that metal-induced renal effects need to be considered when caring for individuals with embedded metal fragment wounds.

Brain region- and metal-specific effects of embedded metals in a shrapnel wound model in the rat

The health effects of prolonged exposure to embedded metal fragments, such as those found in shrapnel wounds sustained by an increasing number of military personnel, are not well known. As part of a large collaborative effort to expand this knowledge, we use an animal model of shrapnel wounds originally developed to investigate effects of embedded depleted uranium to investigate effects of military-relevant metals tungsten, nickel, cobalt, iron, copper, aluminum, lead, and depleted uranium compared to an inert control, tantalum. Rats are surgically implanted with pellets of one of the metals of interest in the gastrocnemius (leg) muscle and tracked until 1 month, 3 months, 6 months, or 12 months from the time of implant, at which point they are euthanized and multiple organs and tissue samples are collected for inspection. Here we focus on four regions of the brain: frontal cortex, hippocampus, amygdala, and cerebellum. We examined changes in accumulated metal concentration in each region as well as changes in expression of proteins related to blood brain barrier tight junction formation, occludin and ZO-1, and synapse function, PSD95, spinophilin, and synaptotagmin. We report few changes in metal accumulation or blood brain barrier protein expression, but a large number of synapse proteins have reduced expression levels, particularly within the first 6 months of exposure, but there are regional and metal-specific differences in effects.

Effects of Incubation of Human Brain Microvascular Endothelial Cells and Astrocytes with Pyridostigmine Bromide, DEET, or Permethrin in the Absence or Presence of Metal Salts

Gulf War Illness (GWI) is a chronic, multi-symptom illness suffered by over one-third of American military veterans who served in the Persian Gulf War between 1990 and 1991. No current single-exposure scenario accounts for all the symptoms observed in GWI, and instead may be due to a multi-exposure scenario. As a larger effort to understand how one category of multi-exposure scenarios of organic compounds such as nerve gas prophylactic pyridostigmine bromide, or insecticides/pesticides such as N,N-diethyl-m-toluamide (DEET) and permethrin, plus heavy metals found in inhaled dust particles (Al, Fe, Ni, Sr, DU, Co, Cu, Mn, and Zn) might play a role in neural aspects of GWI, we begin this initial study to examine the toxicity and oxidative damage markers of human brain endothelial cell and human astrocyte cell cultures in response to these compounds. A battery of cytotoxicity assessments, including the MTT assay, Neutral Red uptake, and direct microscopic observation, was used to determine a non-toxic dose of the test compounds. After testing a wide range of doses of each compound, we chose a sub-toxic dose of 10 µM for the three organic compounds and 1 µM for the nine metals of interest for co-exposure experiments on cell cultures and examined an array of oxidative stress-response markers including nitric oxide production, formation of protein carbonyls, production of thiobarbituric acid-reactive substances, and expression of proteins involved in oxidative stress and cell damage. Many markers were not significantly altered, but we report a significant increase in nitric oxide after exposure to any of the three compounds in conjunction with depleted uranium.

Time-course analysis of the effect of embedded metal on skeletal muscle gene expression

As a consequence of military operations, many veterans suffer from penetrating wounds and long-term retention of military-grade heavy metal fragments. Fragments vary in size and location, and complete surgical removal may not be feasible or beneficial in all cases. Increasing evidence suggests retention of heavy metal fragments may have serious biological implications, including increased risks for malignant transformation. Previous studies assessed the tumorigenic effects of metal alloys in rats, demonstrating combinations of metals are sufficient to induce tumor formation after prolonged retention in skeletal muscle tissue. In this study, we analyzed transcriptional changes in skeletal muscle tissue in response to eight different military-relevant pure metals over 12 mo. We found that most transcriptional changes occur at 1 and 3 mo after metal pellets are embedded in skeletal muscle and these effects resolve at 6 and 12 mo. We also report significant immunogenic effects of nickel and cobalt and suppressive effects of lead and depleted uranium on gene expression. Overall, skeletal muscle exhibits a remarkable capacity to adapt to and recover from internalized metal fragments; however, the cellular response to chronic exposure may be restricted to the metal-tissue interface. These data suggest that unless affected regions are specifically captured by biopsy, it would be difficult to reliably detect changes in muscle gene expression that would be indicative of long-term adverse health outcomes.

Hydrophobic sand is a viable method of urine collection from the rat for extracellular vesicle biomarker analysis

Previously we have shown in rats a new method of urine collection, hydrophobic sand, to be an acceptable alternate in place of the traditional method using metabolic cages. Hydrophobic sand is non-toxic, induces similar or lower levels of stress in the rat, and does not contaminate clinical urine markers nor metal concentrations in collected samples (Hoffman et al., 2017 and 2018). Urine is often used in humans and many animal models as a readily-attainable biosample which contains proteins and microRNAs (miRNAs) within extracellular vesicles (EVs) that can be isolated to indicate changes in health. In order to ensure hydrophobic sand did not in any way contaminate or disrupt the extraction and analysis of these EVs and miRNAs, we used urine samples from the same 8 rats in the within-subjects crossover experiment comparing hydrophobic sand and metabolic cage collection methods. We isolated EVs and miRNAs from the urine set and examined their quantity and quality between the urine collection methods. We found no significant differences in particle size, particle concentration, total RNA, or the type and abundance of miRNAs contained within the urine EVs due to urine collection method, suggesting hydrophobic sand represents an easy-to-use, non-invasive method to collect rodent urine for EVs and biomarker studies.

Hydrophobic Sand Versus Metabolic Cages: A Comparison of Urine Collection Methods for Rats (Rattus norvegicus)

A common method for urine collection from rats requires the use of a metabolic cage, thus exposing animals to extended periods of isolation in an unfamiliar cage with a wire-mesh floor. A new method involving hydrophobic sand, a material more similar to bedding, has become available recently but has not been extensively compared with metabolic cages in regard to collection efficiency or stress. Using a within-subjects crossover design, we examined differences in stress markers, urinary markers, and urine volume of clinically healthy male Sprague-Dawley rats during 2-, 4-, and 6-h collection sessions in hydrophobic sand and metabolic cages. Stress response markers of weight loss, fecal pellet output, or corticosterone did not differ between hydrophobic sand and metabolic cages, and observed behavior suggested that sand may be less stressful than metabolic cages. All clinically relevant urinary markers examined were normal, with no differences between collection methods. Total urine volume collected was greater from the metabolic cage than sand in 3 of the 5 sessions, but the volume collected during the shortest session (2 h) did not differ between methods and accounted for 62% of the total volume collected during the longest session (6 h). Our results suggest that hydrophobic sand is a refinement of urine collection methods for rats that decreases isolation time, risk of injury, and stress and maintains the integrity of urine samples.

Hydrophobic Sand Is a Non-Toxic Method of Urine Collection, Appropriate for Urinary Metal Analysis in the Rat

Hydrophobic sand is a relatively new method of urine collection in the rodent, comparable to the established method using a metabolic cage. Urine samples are often used in rodent research, especially for biomarkers of health changes after internal contamination from embedded metals, such as in a model of a military shrapnel wound. However, little research has been done on the potential interference of hydrophobic sand with urine metal concentrations either by contamination from the sand particulate, or adsorption of metals from the urine. We compare urine collected from rats using the metabolic cage method and the hydrophobic sand method for differences in metal concentration of common urinary metals, and examine physical properties of the sand material for potential sources of contamination. We found minimal risk of internal contamination of the rat by hydrophobic sand, and no interference of the sand with several common metals of interest (cobalt, strontium, copper, and manganese), although we advise caution in studies of aluminum in urine.

The ESC/E(Z) complex, an effector of response to ovarian steroids, manifests an intrinsic difference in cells from women with premenstrual dysphoric disorder

Clinical evidence suggests that mood and behavioral symptoms in premenstrual dysphoric disorder (PMDD), a common, recently recognized, psychiatric condition among women, reflect abnormal responsivity to ovarian steroids. This differential sensitivity could be due to an unrecognized aspect of hormonal signaling or a difference in cellular response. In this study, lymphoblastoid cell line cultures (LCLs) from women with PMDD and asymptomatic controls were compared via whole-transcriptome sequencing (RNA-seq) during untreated (ovarian steroid-free) conditions and following hormone treatment. The women with PMDD manifested ovarian steroid-triggered behavioral sensitivity during a hormone suppression and addback clinical trial, and controls did not, leading us to hypothesize that women with PMDD might differ in their cellular response to ovarian steroids. In untreated LCLs, our results overall suggest a divergence between mRNA (for example, gene transcription) and protein (for example, RNA translation in proteins) for the same genes. Pathway analysis of the LCL transcriptome revealed, among others, over-expression of ESC/E(Z) complex genes (an ovarian steroid-regulated gene silencing complex) in untreated LCLs from women with PMDD, with more than half of these genes over-expressed as compared with the controls, and with significant effects for MTF2, PHF19 and SIRT1 (P<0.05). RNA and protein expression of the 13 ESC/E(Z) complex genes were individually quantitated. This pattern of increased ESC/E(Z) mRNA expression was confirmed in a larger cohort by qRT-PCR. In contrast, protein expression of ESC/E(Z) genes was decreased in untreated PMDD LCLs with MTF2, PHF19 and SIRT1 all significantly decreased (P<0.05). Finally, mRNA expression of several ESC/E(Z) complex genes were increased by progesterone in controls only, and decreased by estradiol in PMDD LCLs. These findings demonstrate that LCLs from women with PMDD manifest a cellular difference in ESC/E(Z) complex function both in the untreated condition and in response to ovarian hormones. Dysregulation of ESC/E(Z) complex function could contribute to PMDD.

Prostaglandin E2 stimulates estradiol synthesis in the cerebellum postnatally with associated effects on Purkinje neuron dendritic arbor and electrophysiological properties

Prostaglandins (PGs) are ubiquitous membrane-derived, lipid-signaling molecules with wide ranging effects throughout the body. In the brain, PGE(2) is the key regulator of fever after inflammation but is also implicated in neural development and synaptic plasticity. The steroid hormone estradiol is also a key regulator of neural development and synaptic plasticity. Recently, we showed that administering cyclooxygenase (COX) inhibitors to block PGE(2) production increased the total length of Purkinje cell dendrites, the number of dendritic spines, and the level of spinophilin protein, which is enriched in dendritic spines. Correspondingly, PGE(2) administration into the cerebellum decreased spinophilin protein content. We now report that PGE(2) stimulates estradiol synthesis in the immature rat cerebellum via enhanced activity of the aromatase enzyme. Treatment with cyclooxygenase inhibitors reduced cerebellar aromatase activity and estradiol content whereas PGE(2) administration increased both. Treatment with either PGE(2) or estradiol stunted Purkinje neuron dendritic length and complexity and produced a corresponding reduction in spinophilin content. Treatment with formestane to inhibit aromatase activity led to excessive sprouting of the dendritic tree, whereas elevated estradiol had the opposite effect. Electrophysiological measurements from Purkinje neurons revealed novel sex differences in input resistance and membrane capacitance that were abolished by estradiol exposure, whereas a sex difference in the amplitude of the afterhyperpolarization after an action potential was not. Correlated changes in action potential threshold suggest that prolonged alterations in neuronal firing activity could be a consequence of increased estradiol content during the second week of life. These findings reveal a previously unappreciated role for PG-stimulated steroidogenesis in the developing brain and a new potential route for inflammation-mediated disruption of neuronal maturation.

Large-scale analysis of ion channel gene expression in the mouse heart during perinatal development

The immature and mature heart differ from each other in terms of excitability, action potential properties, contractility, and relaxation. This includes upregulation of repolarizing K(+) currents, an enhanced inward rectifier K(+) (Kir) current, and changes in Ca(2+), Na(+), and Cl(-) currents. At the molecular level, the developmental regulation of ion channels is scantily described. Using a large-scale real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) assay, we performed a comprehensive analysis of ion channel transcript expression during perinatal development in the embryonic (embryonic day 17.5), neonatal (postnatal days 1-2), and adult Swiss-Webster mouse hearts. These data are compared with publicly available microarray data sets (Cardiogenomics project). Developmental mRNA expression for several transcripts was consistent with the published literature. For example, transcripts such as Kir2.1, Kir3.1, Nav1.5, Cav1.2, etc. were upregulated after birth, whereas others [e.g., Ca(2+)-activated K(+) (KCa)2.3 and minK] were downregulated. Cl(-) channel transcripts were expressed at higher levels in immature heart, particularly those that are activated by intracellular Ca(2+). Defining alterations in the ion channel transcriptome during perinatal development will lead to a much improved understanding of the electrophysiological alterations occurring in the heart after birth. Our study may have important repercussions in understanding the mechanisms and consequences of electrophysiological alterations in infants and may pave the way for better understanding of clinically relevant events such as congenital abnormalities, cardiomyopathies, heart failure, arrhythmias, cardiac drug therapy, and the sudden infant death syndrome.

Management of scalp defects

This article presents a systematic approach to the reconstruction of scalp defects, which includes a review of the anatomy of the scalp as it pertains to reconstruction, and a discussion of the various reconstructive options for scalp defects, such as grafts and flaps. Further, scalp flap selection, design, and execution are outlined. Finally, adjunctive techniques of tissue expansion and hair transplants are included to enhance the final aesthetic result.

Cation transport and cell volume changes in maturing rat reticulocytes

During maturation, reticulocytes lose membrane material, including transporters, and this is accompanied by a loss of cell water and volume. Here we determined a possible role of ion transport in adjusting cell volume during maturation. Reticulocytes and red blood cells of different ages were prepared from erythropoietin-treated rats by density gradient fractionation. Cell volume and ion transport were measured in freshly prepared cells and in reticulocytes during in vitro maturation. Reticulocytes had an increased K content and cell volume, whereas intracellular Na was decreased. All parameters approached whole blood values after 2 days in culture. Na-K pump was elevated in reticulocytes and decreased during maturation. Na-K-2Cl cotransport (NKCC) activity was lower in reticulocytes and was activated 8- and 20-fold by shrinkage and okadaic acid, respectively, whereas stimulation was barely detectable in high-buoyant density red blood cells. The ouabain- and bumetanide-insensitive Na flux in reticulocytes decreased on maturation. Most of it was inhibited by amiloride, indicating the presence of Na/proton exchange. Our results show that, although the Na-K-pump activity in reticulocytes is very much increased, the enhanced capacity of NKCC is essentially cryptic until stimulated. Both types of capacities (activities) decrease during maturation, indicating a possible loss of transport protein. The decrease was constrained to the period of reticulocyte maturation. Loss of transport capacity appears to exceed the loss of membrane surface area. Reticulocyte age-related changes in the net electrochemical driving force indicate that the increasing NKCC activity might contribute to the reduction in cell water.

Threshold and graded response behavior in human neutrophils: effect of varying G-protein or ligand concentrations

Observing the qualitative characteristics of response behavior as key variables in the signal transduction cascade are changed can provide insight into the fundamental roles of these interactions in producing cellular responses. Using flow cytometric assays and pertussis toxin (PT) treatment of human neutrophils, we have shown that actin polymerization stimulated with the chemoattractants N-formyl-Met-Leu-Phe, leukotriene B4, and interleukin-8 exhibits threshold behavior in terms of G-protein number. Partial PT treatment resulted in both responding and nonresponding populations of cells upon stimulation. As PT treatment was increased, the responding population of cells continued to respond maximally, while the number of cells responding decreased. We also showed that N-formyl peptide-stimulated oxidant production exhibits threshold behavior in terms of G-protein number, and the threshold for oxidant production is significantly greater than that for actin polymerization. The threshold behavior observed with PT treatment contrasted with the graded response behavior seen when cells were stimulated with different doses of ligand. For actin polymerization, only one population of cells was observed at submaximal ligand concentrations, and as ligand concentration was decreased the whole population responded submaximally. For oxidant production, as ligand concentration was decreased there were two populations of cells, but the responding cells responded submaximally. A mathematical model incorporating receptor/ligand binding and G-protein activation was developed to account for these differences in response behavior. Our results predict that an early signal transduction event in addition to, and not initiated by G-protein activation, is necessary to account for actin polymerization and oxidant production in neutrophils.

Birth trauma causing nasal vestibular stenosis

Nasal vestibular stenosis is caused by a disruption of the nasal vestibular lining with secondary proliferation of granulation and fibrous tissue. It is most commonly the result of significant nasal trauma of foreign body reaction. In the pediatric population, it is exceedingly rare, with only a few cases reported in the literature. We report the first case, to our knowledge, of complete stenosis caused by traumatic vaginal delivery. This case demonstrates the profound effect nasal vestibular stenosis can have on the developing nose. Correction can be difficult because of the tendency of wound contracture and recurrence. A new approach is presented, using a hard palate mucosal graft. This graft is tough, resilient, and easily harvested. Its ability to resist contracture obviates the need for postoperative stenting, which is especially useful in the pediatric population.

Na,K-ATPase subunit isoforms in human reticulocytes: evidence from reverse transcription-PCR for the presence of alpha1, alpha3, beta2, beta3, and gamma

The objective of this study has been to determine which Na,K-ATPase isoforms are expressed in red blood cells and whether kinetic differences in the uncoupled sodium efflux mode between the human red blood cell Na,K-ATPase and other preparations can be explained by differences in the underlying subunit composition. To this end, human reticulocyte RNA was isolated, reverse transcribed, amplified by PCR and appropriate primers, and sequenced. Primers from highly conserved areas as well as isoform-specific primers were used. The alpha1 and alpha3 isoforms of the alpha subunit, and the beta2 and beta3 isoforms of the beta subunit were found. The complete coding regions of the cDNAs for the reticulocyte subunits were sequenced from overlapping PCR fragments. No difference was found between the reticulocyte isoforms and the ones already known. The fact that we found beta2 but not beta1 in reticulocyte single-stranded cDNA, and beta1 but not beta2 in a leukocyte library indicates that leukocyte contamination of our reticulocyte preparation was negligible. Analysis of a human bone marrow library showed that alpha1, alpha2, and alpha3 as well as all three beta isoforms were present. The extent to which the kinetic properties of uncoupled sodium efflux might depend on different isoform combinations is not yet known.

ATP compartmentation in human erythrocytes

This review covers not only the current status of the field but also the evidence on which the concept of ATP compartmentation is based. It is hoped that such a survey may help to stimulate work in this area and to broaden the appreciation of its reality and functions. Some may be surprised to learn that mature human erythrocytes, known to be devoid of intracellular organelles, can sequester ATP, but they may not have taken into account the possible roles of the complex cytoskeleton that is tethered to the cells' plasma membrane. The functional significance of the ATP pools springs from the likelihood that they serve as both an energy reserve, capable of sustaining ion pumping during periods of transient stress, as well as a putative transduction mechanism by which the cell's cytoskeleton may sense cellular energy stores.

Interconverting receptor states at 4 degrees C for the neutrophil N-formyl peptide receptor

With the aid of high time resolution kinetic data extracted from a flow cytometer, we determined that there are two N-formyl peptide receptor states for human neutrophils at 4 degrees C: a low affinity and a high affinity state. Competitive binding of FMLP, FNLP, and t-BOC with FNLPNTL-FL revealed different kinetic rate constants for two distinct reactions that control the lifetime of the low affinity ligand-receptor complex. For these ligands, the rate constant for dissociation of ligand from the low affinity receptor state (the first reaction) ranges in order of magnitude from 10(-2) to 1 s-1, and the conversion rate constant from the low affinity receptor state to the high affinity receptor state (the second reaction) ranges from 10(-4) to 10(-2) s-1. The antagonist t-BOC differed most significantly from the three agonists by having an association rate constant for the low affinity receptor on the order of 10(5) M-1 s-1; the value for all three agonists was on the order of 10(7) M-1 s-1. Characterization of the receptor conversion at 4 degrees C revealed that it is irreversible (or very slow) and independent of Gi protein and that neither receptor state is a form of receptor precoupled to Gi protein. The affinity conversion and the dissociation characteristics of each receptor state determine the duration of the signaling complex and may contribute to differences in ligand efficacy.

Receptor up-regulation, internalization, and interconverting receptor states. Critical components of a quantitative description of N-formyl peptide-receptor dynamics in the neutrophil

High resolution kinetic data of the binding of fluorescent peptide to the N-formyl peptide receptor of neutrophils at 37 degrees C has allowed for the development of a ligand binding model that predicts statistically larger binding rate constants than those previously reported for intact neutrophils. The new model accounts for ligand association and dissociation, receptor up-regulation, ligand-receptor complex internalization, a change in receptor affinity, and the quenching of internalized fluorescent ligand. We determined that receptor up-regulation is both agonist- and temperature-induced and is inhibited by both phenylarsine oxide and pertussis toxin treatment. Model fits of ligand association to pertussis toxin-treated cells show that while receptor up-regulation was inhibited, rate constants for ligand binding, receptor affinity conversion, and internalization of ligand-receptor complexes were unaffected. Results suggest Gi-protein-mediated receptor up-regulation and Gi-protein-independent receptor affinity conversion. Simulation of ligand infusion using our model gives insight into the quantitative and dynamic relationship between the low affinity ligand-receptor complex and the actin polymerization response.

Rapid oscillations of actin polymerization/depolymerization in polymorphonuclear leukocytes stimulated by leukotriene B4 and platelet-activating factor

We previously showed that activation of polymorphonuclear leukocytes by leukotriene B4 (LTB4) and platelet-activating factor produces a rapidly oscillating actin polymerization/depolymerization response. In this study, we show that 1) oscillations are not due to the stimulated cyclic release of autocoids that could bind to cell surface receptors and activate subsequent cycles; 2) oscillations are not related to oscillations of ligand binding; and 3) the particular kinetic pattern is a property of the receptor, not of the binding constants of the ligand. The major conclusion of these studies is that the oscillations are a property of the intrinsic signaling pathways triggered by these chemoattractants. We also questioned whether increased actin nucleation activity was induced by LTB4 and found that, although LTB4 induced a transient actin nucleation response, there was not a direct correlation between oscillations of the actin polymerization/depolymerization and the actin nucleation activity. This suggests that processes other than actin nucleation, such as release of monomeric actin from monomer sequestering proteins and regulation of depolymerization, are likely to be involved.

Rapid oscillations of actin polymerization/depolymerization in polymorphonuclear leukocytes stimulated by leukotriene B4 and platelet-activating factor

We previously showed that activation of polymorphonuclear leukocytes by leukotriene B4 (LTB4) and platelet-activating factor produces a rapidly oscillating actin polymerization/depolymerization response. In this study, we show that 1) oscillations are not due to the stimulated cyclic release of autocoids that could bind to cell surface receptors and activate subsequent cycles; 2) oscillations are not related to oscillations of ligand binding; and 3) the particular kinetic pattern is a property of the receptor, not of the binding constants of the ligand. The major conclusion of these studies is that the oscillations are a property of the intrinsic signaling pathways triggered by these chemoattractants. We also questioned whether increased actin nucleation activity was induced by LTB4 and found that, although LTB4 induced a transient actin nucleation response, there was not a direct correlation between oscillations of the actin polymerization/depolymerization and the actin nucleation activity. This suggests that processes other than actin nucleation, such as release of monomeric actin from monomer sequestering proteins and regulation of depolymerization, are likely to be involved.

Comparative aspects of Na+/K+ pump-mediated uncoupled Na+ efflux in red blood cells and kidney proteoliposomes

Ouabain-sensitive uncoupled Na+ efflux has been studied in human, pig, and rat red cells and in vesicles containing reconstituted kidney Na+/K+ pumps obtained from these same species. The red cells from the different species gave qualitatively similar results; the uncoupled Na+ efflux was 15-30% of the Na+/K+ exchange rate, and this flux was inhibited at 5 mM extracellular Na+ (Na+o). At higher levels of Na+o there was a monotonic increase in the Na+ efflux. As has previously been observed in human red cells, the uncoupled efflux from pig red cells consists of Na+ and anion cotransport, suggesting that anion cotransport may be a general characteristic of uncoupled Na+ efflux in red cells. The uncoupled Na+ efflux carried out by pig and rat kidney Na+/K+ pumps differs from the red cell activity in that it represents no more than 2-4% of the Na+/K+ exchange rate and that 5 mM Na+o does not inhibit this efflux. Furthermore, the efflux does not appear to be dependent on anion cotransport. Vesicles containing human kidney Na+/K+ pumps differ from vesicles derived from pig or rat kidneys in that the Na+ efflux is not inhibited or stimulated by Na+ present on the opposite side; it thus appears that the Na+,K(+)-ATPase in these vesicles may be incapable of Na+/Na+ exchange. These results indicate that the ligand and kinetic properties of the uncoupled Na+ efflux mode of red cells are markedly different from kidney-derived Na+/K+ pumps reconstituted into proteoliposomes. The basis for these differences may be inherent in the Na+/K+ pumps themselves or represent differences between the two types of preparations studied.

Phosphate from the phosphointermediate (EP) of the human red blood cell Na/K pump is coeffluxed with Na, in the absence of external K

This study is concerned with Na/K pump-mediated phosphate efflux that occurs during uncoupled Na efflux in human red blood cells. Uncoupled Na efflux is known to be a ouabain-sensitive mode of the Na/K pump that occurs in the absence of external Nao and Ko. Because this efflux (measured with 22Na) is also inhibited by 5 mM Nao, the efflux can be separated into a Nao-sensitive and a Nao-insensitive component. Previous work established that the Nao-sensitive efflux is actually comprised of an electroneutral coefflux of Na with cellular anions, such as SO4 (as 35SO4). The present work focuses on the Nao-insensitive component in which the principal finding is that orthophosphate (P(i)) is coeffluxed with Na in a ouabain-sensitive manner. This P(i) efflux can be seen to occur, in the absence of Ko, in both DIDS-treated intact cells and resealed red cell ghosts. This efflux of P(i) was shown to be derived directly from the pump's substrate, ATP, by the use of resealed ghosts made to contain both ATP and P(i) in which either the ATP or the P(i) were labeled with, respectively, [gamma-32P]ATP or [32P]H3PO4. (These resealed ghosts also contained Na, Mg, P(i), SO4, Ap5A, as well as an arginine kinase/creatine kinase nucleotide regenerating system for the control of ATP and ADP concentrations, and were suspended usually in (NMG)2SO4 at pH 7.4.) It was found that 32P was only coeffluxed with Na when the 32P was contained in [gamma-32P]ATP and not in [32P]H3PO4. This result implies that the 32P that is released comes from ATP via the pump's phosphointermediate (EP) without commingling with the cellular pool of P(i). Ko (as K2SO4) inhibits this 32P efflux as well as the Nao-sensitive 35SO4 efflux, with a K0.5 of 0.3-0.4 mM. The K0.5 for inhibition of P(i) efflux by Ko is not influenced by Nao, nor can Nao act as a congenor for Ko in any of the flux reactions involving Ko. The stoichiometry of Na to SO4 and Na to P(i) efflux is approximately 2:1 under circumstances where the stoichiometry of Na effluxed to ATP utilized is 3:1. From these and other results reported, it is suggested that there are two types of uncoupled Na efflux that differ from each other on the basis of their sensitivity to Nao, the source (cellular vs substrate) and kind of anion (SO4 vs P(i)) transported.(ABSTRACT TRUNCATED AT 400 WORDS)

ADP+orthophosphate (P(i)) stimulates an Na/K pump-mediated coefflux of P(i) and Na in human red blood cell ghosts

The Na/K pump in human red blood cells that normally exchanges 3 Nai for 2 Ko is known to continue to transport Na in a ouabain-sensitive and ATP-dependent manner when the medium is made free of both Nao and Ko. Although this Na efflux is called "uncoupled" because of removal of ions to exchange with, the efflux has been shown to be comprised of a coefflux with cellular anions. The work described in this paper presents a new mode of operation of uncoupled Na efflux. This new mode not only depends upon the combined presence of ADP and intracellular orthophosphate (P(i))i but the Na efflux that is stimulated to occur is coeffluxed with (P(i))i. These studies were carried out with DIDS-treated resealed red cell ghosts, suspended in buffered (NMG)2SO4, that were made to contain, in addition to other constituents, varying concentrations of ADP and P(i) together with Na2 SO4, MgSO4 and hexokinase. While neither ADP nor P(i) was effective alone, ouabain-sensitive uncoupled Na efflux, (measured with 22Na) could be activated by [ADP+P(i)] where the K0.5 for ADP in the presence of 10 mmol (P(i))i/liter ghosts was 100-200 mumol/liter ghosts and the K0.5 for (P(i))i, in the presence of 500 mumol ADP/liter ghosts was 3-4 mmol/liter ghosts. [ADP+P(i)] activation of this Na efflux could be inhibited by as little as 2 mumol ATP/liter ghosts but the inhibition could be relieved by the addition of 50 mM glucose, given entrapped hexokinase. While ouabain-sensitive Na efflux was found to be coeffluxed with P(i) (measured with entrapped [32P]H3PO4), this was not so for SO4 (measured with 35SO4). The stoichiometry of Na to P(i) efflux was found to be approximately 2 to 1. Na efflux as well as (P(i))i efflux were both inhibited by 10 mM Nao (K0.5 approximately equal to 4 mM). But, whereas 20 mM Ko (K0.5 approximately equal to 6 mM) inhibited the efflux of (P(i))i, as would be expected from previous work, Na efflux was actually increased. When Ko influx was measured in this situation there was a 1 for 1 exchange of Nai for Ko, that is, of course, downhill with respect to the gradient of each ion. Surprisingly AsO4 was unable to replace P(i) for activation of Na efflux but Na efflux could be inhibited by vanadate and oligomycin. In terms of mechanism, it is likely that ADP acts to promote the formation of the phosphoenzyme (EP) by (P(i))i that would otherwise be inhibited by Nai.(ABSTRACT TRUNCATED AT 400 WORDS)

Internal magnesium, 2,3-diphosphoglycerate, and the regulation of the steady-state volume of human red blood cells by the Na/K/2Cl cotransport system

This study is concerned with the relationship between the Na/K/Cl cotransport system and the steady-state volume (MCV) of red blood cells. Cotransport rate was determined in unfractionated and density-separated red cells of different MCV from different donors to see whether cotransport differences contribute to the difference in the distribution of MCVs. Cotransport, studied in cells at their original MCVs, was determined as the bumetanide (10 microM)-sensitive 22Na efflux in the presence of ouabain (50 microM) after adjusting cellular Na (Nai) and Ki to achieve near maximal transport rates. This condition was chosen to rule out MCV-related differences in Nai and Ki that might contribute to differences in the net chemical driving force for cotransport. We found that in both unfractionated and density-separated red cells the cotransport rate was inversely correlated with MCV. MCV was correlated directly with red cell 2,3-diphosphoglycerate (DPG), whereas total red cell Mg was only slightly elevated in cells with high MCV. Thus intracellular free Mg (Mgifree) is evidently lower in red cells with high 2,3-DPG (i.e., high MCV) and vice versa. Results from flux measurements at their original MCVs, after altering Mgifree with the ionophore A23187, indicated a high Mgi sensitivity of cotransport: depletion of Mgifree inhibited and an elevation of Mgifree increased the cotransport rate. The apparent K0.5 for Mgifree was approximately 0.4 mM. Maximizing Mgifree at optimum Nai and Ki minimized the differences in cotransport rates among the different donors. It is concluded that the relative cotransport rate is regulated for cells in the steady state at their original cell volume, not by the number of copies of the cotransporter but by differences in Mgifree. The interindividual differences in Mgifree, determined primarily by differences in the 2,3-DPG content, are responsible for the differences in the relative cotransport activity that results in an inverse relationship with in vivo differences in MCV. Indirect evidence indicates that the relative cotransport rate, as indexed by Mgifree, is determined by the phosphorylated level of the cotransport system.

Anion-coupled Na efflux mediated by the human red blood cell Na/K pump

The red cell Na/K pump is known to continue to extrude Na when both Na and K are removed from the external medium. Because this ouabain-sensitive flux occurs in the absence of an exchangeable cation, it is referred to as uncoupled Na efflux. This flux is also known to be inhibited by 5 mM Nao but to a lesser extent than that inhibitable by ouabain. Uncoupled Na efflux via the Na/K pump therefore can be divided into a Nao-sensitive and Nao-insensitive component. We used DIDS-treated, SO4-equilibrated human red blood cells suspended in HEPES-buffered (pHo 7.4) MgSO4 or (Tris)2SO4, in which we measured 22Na efflux, 35SO4 efflux, and changes in the membrane potential with the fluorescent dye, diS-C3 (5). A principal finding is that uncoupled Na efflux occurs electroneurally, in contrast to the pump's normal electrogenic operation when exchanging Nai for Ko. This electroneutral uncoupled efflux of Na was found to be balanced by an efflux of cellular anions. (We were unable to detect any ouabain-sensitive uptake of protons, measured in an unbuffered medium at pH 7.4 with a Radiometer pH-STAT.) The Nao-sensitive efflux of Nai was found to be 1.95 +/- 0.10 times the Nao-sensitive efflux of (SO4)i, indicating that the stoichiometry of this cotransport is two Na+ per SO4=, accounting for 60-80% of the electroneutral Na efflux. The remainder portion, that is, the ouabain-sensitive Nao-insensitive component, has been identified as PO4-coupled Na transport and is the subject of a separate paper. That uncoupled Na efflux occurs as a cotransport with anions is supported by the result, obtained with resealed ghosts, that when internal and external SO4 was substituted by the impermeant anion, tartrate i,o, the efflux of Na was inhibited 60-80%. This inhibition could be relieved by the inclusion, before DIDS treatment, of 5 mM Cli,o. Addition of 10 mM Ko to tartrate i,o ghosts, with or without Cli,o, resulted in full activation of Na/K exchange and the pump's electrogenicity. Although it can be concluded that Na efflux in the uncoupled mode occurs by means of a cotransport with cellular anions, the molecular basis for this change in the internal charge structure of the pump and its change in ion selectivity is at present unknown.

Membrane sidedness and the interaction of H+ and K+ on Ca2(+)-activated K+ transport in human red blood cells

The sided effects of H+ on Ca2(+)-stimulated K+ transport (the Gardos channel) were studied in human red blood cells. Cells were loaded with Ca2+ during energy depletion with the internal pH adjusted to desired levels prior to treatment with the anion-exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), which inhibits pH equilibration across the membrane. This treatment provides a "pH clamp" whereby the internal and external H+ (H+i and H+o) concentrations can be varied separately. Channel activity was evaluated by measuring either net K+ loss or unidirectional 42K+ efflux from cells where SO2(-4) replaced Cl- on both sides of the membrane. When pHi was set at 7.4, decreasing pHo from values of 8.0 to 5.0 inhibited K+ efflux. This effect of H+o could be overcome by increasing K+o at all values of pHo. In addition, this effect of K+o could be separated from its effects on altering the membrane potential, indicating an interaction between K+o and H+o on the channel. A similar interaction was shown to occur between H+i and K+i. K+o is known to be required for activation of Ca2(+)-stimulated K+ transport, since the channel in cells preincubated in the absence of K+o (prior to exposure to Ca+i) becomes refractory to subsequent activation by Ca2+i and K+o. We found that H+o would not substitute for K+o in this regard nor would H+o inhibit the protective effect of K+o; in addition, H+ was not transported inward in exchange for K+i. Thus it would appear that there are two external sites where K+o interacts with the channel. One site is antagonized by H+o, whereas the second site is required for channel activation independent of H+ in the range studied. The inside of the channel would have, by an analogous argument, at least one site where K+i and H+i interact.

Effects of altering the ATP/ADP ratio on pump-mediated Na/K and Na/Na exchanges in resealed human red blood cell ghosts

Resealed human red blood cell ghosts were prepared to contain a range of ADP concentrations at fixed ATP concentrations and vice versa. ATP/ADP ratios ranging from approximately 0.2 to 50 were set and maintained (for up to 45 min) in this system. ATP and ADP concentrations were controlled by the addition of either a phosphoarginine- or phosphocreatine-based regenerating system. Ouabain-sensitive unidirectional Na efflux was determined in the presence and absence of 15 mM external K as a function of the nucleotide composition. Na/K exchange was found to increase to saturation with ATP (K 1/2 approximately equal to 250 microM), whereas Na/Na exchange (measured in K-free solutions) was a saturating function of ADP (K 1/2 approximately equal to 350 microM). The elevation of ATP from approximately 100 to 1,800 microM did not appreciably affect Na/Na exchange. In the presence of external Na and a saturating concentration of external K, increasing the ADP concentration at constant ATP was found to decrease ouabain-sensitive Na/K exchange. The decreased Na/K exchange that still remained when the ADP/ATP ratio was high was stimulated by removal of external Na. Assuming that under normal substrate conditions the reaction cycle of the Na/K pump is rate-limited by the conformational change associated with the release of occluded K [E2 X (K) X ATP----E1 X ATP + K], increasing ADP inhibits the rate of these transformations by competition with ATP for the E2(K) form. A less likely alternative is that inhibition is due to competition with ATP at the high-affinity site (E1). The acceleration of the Na/K pump that occurs upon removing external Na at high levels of ADP evidently results from a shift in the forward direction of the transformation of the intermediates involved with the release of occluded Na from E1P X (Na). Thus, the nucleotide composition and the Na gradient can modulate the rate at which the Na/K pump operates.

Chloride transport properties of human leukemic cell lines K562 and HL60

The Cl- transport characteristics of the human leukemic cell lines K562 and HL60, with erythroid and granulocytic phenotypic features, respectively, were investigated. Cl- effluxes were measured with 36Cl- under equilibrium conditions in both cell lines and were found to be three orders of magnitude slower than the unidirectional efflux of Cl- in normal erythrocytes. Induction of differentiation of the K562 cell line with hemin does not affect the rate of Cl- transport, while induction of the HL60 cell line with dimethyl sulfoxide results in a small decrease in the rate of Cl- transport. Cl- transport in both cell lines could be divided into two components. One component is inhibited by treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), displays counter-transport characteristics, and has a high energy of activation--all properties characteristic of the human erythrocyte-facilitated anion exchange system. The second component is insensitive to DIDS, is partially inhibited by furosemide, and has a low energy of activation.

Interrelations among Na and K content, cell volume, and buoyant density in human red blood cell populations

This study establishes a method for determining the concentration of Na and K in single red blood cells from electron probe microanalysis of a cell's Na and K content. To this end, red blood cells were separated into subpopulations according to their buoyant density by means of bovine serum density gradient centrifugation. Cell water and Na + K contents were then determined in each fraction by conventional analytic methods with cell volume estimated from measurements of hematocrits and cell number. It was found that an inverse relationship obtains between the mean cell volume and buoyant cell density since cells increased in size as density decreased. Although the amount of hemoglobin per cell was found to slightly increase as cell density decreased, hemoglobin concentration showed the inverse relationship, indicating that buoyant cell density differences are primarily the result of differences in hemoglobin concentration. In confirmation of Funder and Wieth (Funder, J., Wieth, J.O. 1966. Scand. J. Lab. Invest. 18:167-180) cell water and cell volume was found to vary directly with the summed content of Na + K. Finally, by means of electron probe microanalysis of single cells, the cellular concentration of hemoglobin was found to vary inversely with the Na + K content, providing a quantitative basis for directly estimating cell volume, and thus ionic concentration, with this technique.

Passive Ca transport in human red blood cell ghosts measured with entrapped arsenazo III

The rate of Ca influx into ghosts containing arsenazo III changes with time, being most rapid during the first 5 min after Ca is added to the outside and declining thereafter. The rate of Ca influx is a nonlinear function of extracellular Ca and plateaus as the latter is increased above 1 mM. The rate of Ca influx was measured as a function of the transmembrane gradients of Na and K and changes in the permeability of the membrane to K and Cl produced by valinomycin and SITS (4-acetamido-4'-isothiocyano-stilbene-2-2'-disulfonic acid), respectively. Changes in the rate of Ca influx are consistent with expected effects of these treatments on the membrane potential. Oligomycin (10 micrograms/ml) and quinidine (1 mM) inhibit the rate of Ca uptake by inhibiting Ca-induced changes in the K permeability. At constant membrane potential, furosemide produced a slight (15%) consistent increase in Ca uptake. Other experiments show that resealed ghosts are heterogeneous in their passive permeability to Ca and that A23187 can be used to effectively eliminate such differences. The results of this paper show that resealed human red cell ghosts containing arsenazo III can be used to continuously monitor intracellular free Ca and to study the factors that influence the permeability of the red cell membrane to Ca.

Ca-induced K transport in human red blood cell ghosts containing arsenazo III. Transmembrane interactions of Na, K, and Ca and the relationship to the functioning Na-K pump

Increasing free intracellular Ca (Cai) from less than 0.1 microM to 10 microM by means of A23187 activated Ca-stimulated K transport and inhibited the Na-K pump in resealed human red cell ghosts. These ghosts contained 2 mM ATP, which was maintained by a regenerating system, and arsenazo III to measure Cai. Ca-stimulated K transport was activated 50% at 2-3 microM free Cai and the Na-K pump was inhibited 50% by 5-10 microM free Cai. Free Cai from 1 to 8 microM stimulated K efflux before it inhibited the Na-K pump, dissociating the effect of Ca on the two systems. 3 microM trifluoperazine inhibited Ca-stimulated K efflux and 0.5 mM quinidine reduced Na-K pumping by 50%. In other studies, incubating fresh intact cells in solutions containing Ca and 0.5 microM A23187 caused the cells to lose K heterogeneously. Under the same conditions, increasing A23187 to 10 microM initiated a homogeneous loss of K. In ATP-deficient ghosts containing Cai equilibrated with A23187, K transport was activated at the same free Cai as in the ghosts containing 2 mM ATP. Neither Cao nor the presence of an inward Ca gradient altered the effect of free Cai on the permeability to K. In these ghosts, transmembrane interactions of Na and K influenced the rate of Ca-stimulated K efflux independent of Na- and K-induced changes in free Cai or sensitivity to Cai. At constant free Cai, increasing Ko from 0.1 to 3 mM stimulated K efflux, whereas further increasing Ko inhibited it. Increasing Nai at constant Ki and free Cai markedly decreased the rate of efflux at 2 mM Ko, but had no effect when Ko was greater than or equal to 20 mM. These transmembrane interactions indicate that the mechanism underlying Ca-stimulated K transport is mediated. Since these interactions from either side of the membrane are independent of free Cai, activation of the transport mechanism by Cai must be at a site that is independent of those responsible for the interaction of Na and K. In the presence of A23187, this activating site is half-maximally stimulated by approximately 2 microM free Ca and is not influenced by the concentration of ATP. The partial inhibition of Ca-stimulated K efflux by trifluoperazine in ghosts containing ATP suggests that calmodulin could be involved in the activation of K transport by Cai.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracellular free Ca and Mg of human red blood cell ghosts measured with entrapped arsenazo III

Arsenazo III in human red cell ghosts is calibrated to measure intracellular concentrations of free Ca and free Mg. This calibration was established by comparing the absorbance of arsenazo III in ghosts to its absorption in solution at 600, 630, and 655 nm as a function of buffered free Ca (0.4 microM to 70 microM), free Mg (0.05 to 5 mM), and free Ca (4 to 50 microM) at constant free Mg (1.2 mM) at three concentrations of total dye (1.09, 10.9, and 109 microM). In both ghosts and in solution the absorbance of the dye at all three wavelengths could be predicted from dissociation constants and molar extinction coefficients determined for a 1:1 complex with the dye and Mg, another with Ca, and a third complex consisting of two molecules of Ca and two of dye. The absorbance of the dye in ghosts at the same concentrations of free Ca, free Mg, and total dye is equal to that in solution multiplied by the percentage hematocrit and divided by 100, which demonstrates that arsenazo III responds the same inside ghosts as it does free in solution. The results of this paper show that arsenazo III can be used to measure quantitatively and to monitor continuously the concentration of intracellular Ca and Mg in red cell ghosts. Use of this method should facilitate the study of Ca-dependent mechanisms of red blood cells.

The link between metabolism and active transport of sodium in human red cell ghosts

Reconstituted human red blood cell ghosts have been used to assay various metabolic intermediates for their role in driving the Na:K pump. ATP was identified as the primary substrate of the pump. The main evidence was based on 1) the finding that the only requirement for activation of the pump was the presence of ATP, whether incorporated directly or generated by an ATP-yielding reaction; 2) the discriminating effects of various metabolic inhibitors; 3) the competition between the pump and hexokinase reaction for ATP; and 4) the difference in effects of adenosine and inosine in activating the pump in energy-depleted ghosts. ADP was found to affect the Na:K pump due to the presence of an adenylate kinase and perhaps because of an effect on the phosphoryl potential. The sidedness of action of the cardiotonic steroid, strophanthidin, was evaluated and found to inhibit the Na:K pump only from the outside of the membrane. Inhibition of the pump by strophanthidin was also found to spare ATP in reconstituted ghosts provided the nonspecific phosphatase activity was suppressed.

The Na:K pump in red cells is electrogenic

The membrane potential, E, of the red cell measured with a fluorescent dye, 3,3'-dipropylthiadicarbocyanine iodide, hyperpolarizes when the Na:K pump is activated by adding external K and depolarizes upon the subsequent addition of ouabain. The electrogenic pump is optimally observed in cells where internal Na+ has been raised, SO2-(4) has replaced Cl-, and SO2-(4) permeability has been inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS)). The change in E associated with the electrogenic component is about 6 mV in human red cells, somewhat smaller in sheep, and larger in duck and Amphiuma red cells. The membrane resistance, Rm, can be estimated from the pump-dependent change in E and from the current flow assumed to be one-third the ouabain-sensitive Na efflux. In human red cells, Rm is about 1 X 10(6) ohm-cm2. Rm calculated from the residual DIDS-insensitive SO2-(4) flux is also about 1 X 10(6) ohm-cm2. The closeness of these two values of Rm is paralleled in the other three types of red cells (even though the absolute values of Rm vary among the four types by a factor of 10), indicating that the net current flow across the membrane can be accounted for by the net transport of Na by the pump.

Anion transport in dog, cat, and human red cells. Effects of varying cell volume and Donnan ratio

Membrane potential and the rate constants for anion self-exchange in dog, cat, and human red blood cells have been shown to vary with cell volume. For dog and cat red cells, the outward rate constants for SO4 and Cl increase while the inward rate constant for SO4 decreases as cells swell or shrink. These changes coincide with the membrane potential becoming more negative as a result of changes in cell volume. Human red cells exhibit a similar change in the rate constants for SO4 and Cl efflux in response to cell swelling, but shrunken cells exhibit a decreased rate constant for SO4 efflux and a more positive membrane potential. Hyperpolarization of shrunken dog and cat red cells is due to a volume-dependent rate constant for SO4 efflux and a more positive membrane potential. Hyperpolarization of shrunken dog and cat red cells is due to a volume-dependent increase in PNa. If this increase in PNa is prevented by ATP depletion or if the outward Na gradient is removed, the response to shrinking is identical to human red cells. These results suggest that the volume dependence of anion permeability may be secondary to changes in the anion equilibrium ratio which in red cells is reflected by the membrane potential. When the membrane potential and cell volume of human red cells were varied independently by a method involving pretreatment with nystatin, it was found that the rate of anion transport (for SO4 and Cl) does not vary with cell volume but rather with membrane potential (anion equilibrium ratio); that is, the rate constant for anion efflux is decreased and that for influx is increased as the membrane potential becomes more positive (internal anion concentration increases) while the opposite is true with membrane hyperpolarization (a fall in internal anion concentration).

Direct photoaffinity labeling of the primary region of the ouabain binding site of (Na+ + K+)-ATPase with [3H]ouabain, [3H]digitoxin and [3H]digitoxigenin

The tritiated cardiotonic steroids, ouabain, digitoxin, and digitoxigenin are shown to photolabel the large polypeptide but not the glycoprotein or proteolipid component of the (Na+ + K+)-ATPase when they are bound to the inhibitory site and exposed to light of 220 or 254 nm. The extent of photolabeling is low, less than 1%, and is limited by photocross-linking of the enzyme. The mechanism of photoincorporation does not appear to be either photolysis of the lactone ring in ouabain or photolysis of tryptophan or tyrosine residues in the polypeptide.

Ionic and osmotic equilibria of human red blood cells treated with nystatin

Human red blood cells have been incubated in the presence of nystatin, which allows Na and K, as well as Cl and pH to equilibrate rapidly when cell volume is set with external impermeant sucrose. The intracellular mean ionic activity coefficients, relative to values in the extracellular solution, for KCl and NaCl are 1.01 +/- 0.02 and 0.99 +/- 0.02 (SD, n = 10), respectively, and are independent of external pH, pH o, and of [sucrose]o. With nystatin the dependence of red cell volume on [sucrose]o deviates from ideal osmotic behavior by as much as a factor of three. A virial equation for the osmotic coefficient, phi, of human hemoglobin, Hb, accounts for the cell volumes, and is the same as that which describes Adair's measurements of phi Hb for Hb isolated from sheep and ox bloods. In the presence of nystatin the slope of the acid-base titration curve of the cells is independent of cell volume, implying that the charge on impermeant cellular solutes is independent of Hb concentration at constant pH. By modifying the Jacobs-stewart equations (1947. J. Cell. Comp. Physiol. 30: 79--103) with the osmotic coefficients of Hb and of salts, a nonideal thermodynamic model has been devised which predicts equilibrium Donnan ratios and red cell volume from the composition of the extracellular solution and from certain parameters of the cells. In addition to accounting for the dependence of cell volume on osmotic pressure, the model also describes accurately the dependence of Donnan ratios and cell volumes on pHo either in the presence or absence of nystatin.

Characteristics of anion transport in cat and dog red blood cells

Self-exchange of chloride and sulfate in dog and cat red cells has been measured under equilibrium conditions. The rats of efflux for these anions are approximately twofold higher in dog compared to cat red blood cells. Although the rates differ, the anion exchange systems of these two red cell types exhibit many common properties. The dependence of 35SO4 efflux on the intracellular SO4 concentration, the pH dependence and the inhibition of 35SO4 efflux by Cl and SITS are almost identical in dog and cat red cells. Nystatin treatment was used to study the dependence of 36Cl efflux on internal Cl. Chloride efflux exhibits saturation in both cell types with dog red cells possessing a higher Vmax and K1/2 than cat red cells. The number of anion transport sites was estimated by extrapolation to the number of molecules of dihydro DIDS (H2DIDS, where DIDS is 4,4'-diisothiocyano-2,2' stilbene-disulfonic acid) which were bound at 100% inhibition of transport. The results indicate that either the turnover numbers for anion transport differ in dog, cat, and human red cells or that there is heterogeneity in the function of the membrane components which bind H2DIDS.