Southern ocean carbon and heat impact on climate

The Southern Ocean greatly contributes to the regulation of the global climate by controlling important heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal timescales are therefore impacted by oceanic processes taking place in the Southern Ocean, yet too little is known about these processes. Limitations come both from the lack of observations in this extreme environment and its inherent sensitivity to intermittent processes at scales that are not well captured in current Earth system models. The Southern Ocean Carbon and Heat Impact on Climate programme was launched to address this knowledge gap, with the overall objective to understand and quantify variability of heat and carbon budgets in the Southern Ocean through an investigation of the key physical processes controlling exchanges between the atmosphere, ocean and sea ice using a combination of observational and modelling approaches. Here, we provide a brief overview of the programme, as well as a summary of some of the scientific progress achieved during its first half. Advances range from new evidence of the importance of specific processes in Southern Ocean ventilation rate (e.g. storm-induced turbulence, sea-ice meltwater fronts, wind-induced gyre circulation, dense shelf water formation and abyssal mixing) to refined descriptions of the physical changes currently ongoing in the Southern Ocean and of their link with global climate. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Household deprivation, comorbidities and COVID-19 hospitalization in 690,115 children/adolescents

Background

Studies document that adults in disadvantaged socio-economic positions have elevated risks of a severe course of COVID-19, but it is unclear if this holds true for children. We investigate in this population-based study whether young people from socio-economically disadvantaged households in Germany had a higher risk of COVID-19 hospitalization compared with more affluent counterparts. We also examined if differences were related to comorbidities that predict severe courses in children.

Methods

We included data from all 690,115 children and adolescents (0-18 years) enrolled in a statutory health insurance carrier. Daily hospital diagnoses of COVID-19 were recorded from 1.1.2020 to 13.7.2021. Logistic regressions were used to compare children from households with an indication of poverty (e.g. long- or short-term unemployed) with children from households with insurance holders in regular employment. We also assessed socio-economic characteristics of the area of residence. We controlled for age, sex, days under observation, nationality, and comorbidities (e.g. obesity).

Findings

A COVID-19 hospital diagnosis was a rare event (n = 1637). Children of long-term unemployed parents had a 1·36 times (95% CI 1·21-1·51) higher adjusted odds of hospitalization compared with those of employed parents. Elevated odds were also found for short-term unemployed or low-wage employment. Those living in poor areas had a 3·02 (1·81-5·22) higher odds of hospitalization than those in less deprived areas. Comorbidities were strongly related to hospitalization, but their adjustment did not change main estimates for household deprivation.

Discussion

Results suggest that children from poor households are at higher risk of severe courses of COVID-19 than their affluent counterparts. This underlies the need to implement effective Public Health strategies to protect deprived children from COVID-19 and other infectious disease even in high income countries such as Germany.

Key messages

• Children and adolescents from poor families seem to be at higer risk for sever courses of COVID-19.

• Comorbidities were no key mediating factor in this study.

[Decision criteria for the appropriateness of inpatient treatment in patients with peripheral angiopathy]

In various medical subspecialties like angiology, invasive diagnostic procedures and elective therapy, which under certain conditions may be carried out on outpatients, represent a large proportion of all inpatient medical treatment. As regulations for the statutory health insurance in Germany demand that medical procedures should be preferentially carried out in outpatient facilities, there is a high potential for conflicting views with respect to the question whether hospitalisation of an individual patient is mandatory for medical reasons. Explicit criteria may be useful to prevent conflicting views and to increase truth and fairness in the proceedings of hospitals on one hand and the medical service of the statutory health insurance on the other hand. With respect to this problem we present decision criteria which were compiled by a hospital (Hochrhein-Eggberg-Klinik Bad Säckingen) and the medical service of the statutory health insurance in the state of Baden-Württemberg (MDK-Baden-Württemberg). Our model has proven to be of value in our practical experience. It seems to be transferable to medical subspecialties with similar problems.

[Guidance of medical experts]

Guidance is an issue of growing importance for physicians responsible for medical experts working in public health services and on medical advisory boards. The challenge of ethics on the one hand and the constraints of economy on the other hand have considerable impact on the demands for quantity as well as quality of the expert opinions. Thus, executive staff in these organisations reflect as to whether and how they can influence performance through guidance. A short summary of the results of research on the subject of guidance - concerning the aspects (i) guidance as an interaction of people, (ii) guidance as a task in a concrete situation and (iii) guidance as a systemic process of development - shows and points out a wide range of possibilities for staff management and personnel development of medical consultants. Guidance of medical experts is possible and necessary in order to develop the professionalism of medical experts, in order to ensure quality, conformity to standards and efficiency of medical expertise, as well as for a future-oriented development of the medical advisory boards themselves.

[Case payments in hospital psychiatry in the USA. The Inpatient Psychiatric Facility Prospective Payment System (IPF PPS)]

OBJECTIVE

In Germany the introduction of a prospective payment system (PPS) is intended for inpatients hospitalised in psychiatric facilities. We investigate the various elements of the Prospective Payment System for Inpatient Psychiatric Facilities (IFP PPS) which was established in the USA in 2005 with respect to their potential to be incorporated into a german PPS.

RESULTS

The most important elements of IFP PPS (impact of diagnosis, comorbidity, patient age, per diem adjustment for length of stay, various other adjustment factors like facility characteristics and geographical factors) are presented. The IFP PPS was especially designed for the requirements of psychiatric inpatient facilities in the USA. Complexity of the individual elements of the PPS appears to be manageable. However, various elements, e. g. the facility based adjustments including wage index or rural location and cost of living adjustments will not be applicable to countries other than the US. The 15 diagnosis related groups of the IFP PPS system refer to ICD-9 which is less differentiated than the ICD-10 which is in use in Germany, thus these psychiatric DRG will not be compatible under conditions of a german PPS. The per diem adjustment for length of stay is the predominating element of the IFP PPS, relation to effort/performance is insufficiently represented.

CONCLUSION

Some elements of the IFP PPS may be applicable to a german prospective payment system for psychiatric inpatient facilities, especially with respect to the rules for per diem adjustment for length of stay and for handling of cases with frequent discharge and readmission of patients. Altogether a stronger representation of elements of performance of inpatient facilities seems to be desirable.

[How nationally concordated measures for quality assurance in clinical care of term and preterm infants are put into practice in Baden-Württemberg]

BACKGROUND

By the end of the year 2007, pediatric hospitals in Baden-Württemberg had assigned themselves to one of three levels of perinatal care according to a checklist of the German Federal Joint Committee (F-JC) effective since January 1st, 2006. The Medical Service of Statutory Health Insurance had been assigned to prove the plausibility of that self-assessment according to quality criteria for clinical care of term and preterm newborn infants concordated by the F-JC.

METHODS

Between November 2007 and October 2008 31 providers were audited. Observations were documented in a checklist, reviewed and evaluated by expert auditors. For that purpose, quality criteria given by the F-JC were grouped into 7 quality categories which were weighted according to their practical relevance. In addition, a graded numeric system of evaluation was used for comparative analysis (absolute and relative benchmarking values).

RESULTS

3 of 23 providers fulfilled the quality criteria of the F-JC for PNC level 1 (highest level of care), 6 of 23 fulfilled them in part, and 14 of 23 did not fulfill them as judged by the auditors. Criteria for PNC level 2 were "fulfilled in part" by 2 of 6 providers and "not fulfilled" by 4. Both providers of perinatal special care ("level 3") fulfilled the quality criteria for "level 3" completely. There was no linear correlation between absolute or relative benchmarking values and assessment by expert auditors.

CONCLUSION

If the criteria of the F-JC were interpreted very strictly, it would be difficult to guarantee comprehensive regional delivery of care in the state of Baden-Württemberg at the level formally requested by the F-JC for PNCs.

DRG-Prüfergebnisse im Ländervergleich: MDK Baden-Württemberg und MDK Westfalen-Lippe

We report on the first detailed comparison of evaluation results regarding the correct billing in the G-DRG (German diagnosis-related group) system. For two Medical Review Boards of the Statutory Health Insurance Funds of comparable size (MDK Baden-Württemberg and MDK Westfalen-Lippe), we analysed consecutive expertises regarding correct billing according to section sign 275 SGB V, and the results were compared in terms of the frequency of DRG-relevant error codes, their relevance to revenue, and the question of error clustering (specific DRGs, primary diagnoses, etc.). The analysis comprised 51,010 individual expertises pertaining to billings of the year 2005 (admittance to hospital from January 1 to December 31, 2005). The proportion of disapproved cases was 38.5% in Baden-Württemberg and 44.6% in Westfalen-Lippe. Among these, errors to the disadvantage of the Health Insurance (incorrectly high) were 33.9% and 39.3%, respectively, and errors to the disadvantage of the hospitals (incorrectly low) were 4.6% and 5.3%, respectively. The resulting ratio (incorrectly high vs. low) was an identical 7.4 in both cases. Not only the most commonly rejected DRGs but also the primary and secondary diagnoses were similar in both cases, while the disapproved procedure codes showed a significant variability (analysis based on the respective 10 most common objections). We discuss the similarities and differences in these results and their possible causes, and demonstrate the cost relevance of this audit segment. Result comparisons of this type can yield insights into streamlining of the review practice of Medical Review Boards, as well as increase the efficiency and effectiveness of the selection of cases.

Die Neugeborenensepsis in DRG-System

INTRODUCTION

The introduction of Diagnosis Related Groups in Germany (G-DRG) has brought forward the obligation for physicians to take into account an intricate system of medical, economical and legal implementations. Mistakes in the process of encoding the principal diagnosis or procedures may have financial consequences. Problems to determine the correct ICD-code will be most prominent for diseases with poorly defined or even inconsistent diagnostic criteria as is the case for neonatal septicemia. We decided to evaluate whether the introduction of G-DRG resulted in a change of frequency of the diagnosis "neonatal septicemia".

METHODS

We analysed data derived from the quality assurance program "Neonatalerhebung" in the state of Baden-Württemberg during the years of 2001 through 2004, i. e., 2 years before and 2 years during the introduction of G-DRG. During this period an annual number of 12,316 up to 13,172 newborns were admitted to the participating hospitals.

RESULTS

The mean number of diagnoses per patient increased from 2.2 to 3.8. The frequency of the diagnosis of septicemia remained constant. The percentage of newborns receiving antibiotic therapy did not change. The ratio of cases with "septicemia yes" over "antibiotics yes" did not change. Although it is difficult to determine the diagnosis of neonatal septicemia and in spite of the economic implications of this diagnosis, no change in the frequency of this diagnosis occurred during the introduction of DRG.

CONCLUSIONS

Assuming that the participating hospitals used an identical database for the quality assurance program "Neonatalerhebung" and for accounting, we conclude that the DRG system is stable with respect to neonatal septicemia.

Quantitative trait loci associated with AutoFOM grading characteristics, carcass cuts and chemical body composition during growth of Sus scrofa

A three-generation full-sib resource family was constructed by crossing two commercial pig lines. Genotypes for 37 molecular markers covering chromosomes SSC1, SSC6, SSC7 and SSC13 were obtained for 315 F2 animals of 49 families and their parents and grandparents. Phenotypic records of traits including carcass characteristics measured by the AutoFOM grading system, dissected carcass cuts and meat quality characteristics were recorded at 140 kg slaughter weight. Furthermore, phenotypic records on live animals were obtained for chemical composition of the empty body, protein and lipid accretion (determined by the deuterium dilution technique), daily gain and feed intake during the course of growth from 30 to 140 kg body weight. Quantitative trait loci (QTL) detection was conducted using least-squares regression interval mapping. Highest significance at the 0.1% chromosome-wise level was obtained for five QTL: AutoFOM belly weight on SSC1; ham lean-meat weight, percentage of fat of primal cuts and daily feed intake between 60 and 90 kg live weight on SSC6; and loin lean-meat weight on SSC13. QTL affecting daily gain and protein accretion were found on SSC1 in the same region. QTL for protein and lipid content of empty body at 60 kg liveweight were located close to the ryanodine receptor 1 (RYR1) locus on SSC6. On SSC13, significant QTL for protein accretion and feed conversion ratio were detected during growth from 60 to 90 kg. In general, additive genetic effects of alleles originating from the Piétrain line were associated with lower fatness and larger muscularity as well as lower daily gain and lower protein accretion rates. Most of the QTL for carcass characteristics were found on SSC6 and were estimated after adjustment for the RYR1 gene. QTL for carcass traits, fatness and growth on SSC7 reported in the literature, mainly detected in crosses of commercial lines x obese breeds, were not obtained in the present study using crosses of only commercial lines, suggesting that these QTL are not segregating in the analysed commercial lines.

Qualitätsprüfungen ambulanter Pflegedienste in Baden-Württemberg - Überblick über die Erfahrungen aus 6 Jahren flächendeckender Untersuchungen durch den MDK

During the years 1997 to 2003 the medical services of the statutory health insurance in the German Federal State of Baden-Württemberg carried out a total survey regarding structure, process and outcome with regard to the quality of care of outpatients in the German long-term care insurance system. This survey provides information on the development of the quality of care. All outpatient nursing services licensed by the statutory long-term care insurance funds in Baden-Württemberg (n (1997 - 2000) = 863; n (2000 - 2003) = 779) were subjected to a uniform assessment based on a consented concept applied in all German Federal States. Our results demonstrate a tendency to fewer but larger nursing services providing care for an increasing number of patients. Qualification of head nurses and of caregiving staff in general has significantly improved. Information for the patient/consumer on the conditions of contracts which have to be made between a nursing service and the patient is still deficient in more than 20 % of cases. Adherence to proper procedures in the process of nursing has improved, especially with respect to taking a complete medical/nursing history and defining the individual resources of a patient and aims for therapy/nursing. However, only in (1/3) of the cases could we find a documentation of continuous adaptation of the planning of therapy. Efforts of in-house quality management and internal quality assurance by the outpatient nursing services have improved. Regarding the outcome of nursing there has been a decrease in the provision of stimulating care from 87 % of cases to 75 %. The majority of patients of outpatient nursing services do not receive benefits of the long-term care insurance system but of the statutory health insurance. This fact underlines the importance of a general conceptual framework for internal and external quality assurance.

Begutachtung von Vorsorge- und Rehabilitationsleistungen in der GKV

New Directives of the Federal Joint Committee Concerning Medical Rehabilitation Measures ("Rehabilitation Directives") came into force on 1 (st) April 2004. In this context, a survey of the expert assessment given by the Medical Service of the Statutory Health Insurance ("Medizinischer Dienst der Krankenversicherung, MDK") is provided -- as far, as medical prevention and rehabilitation are concerned.

[Quality project in invasive/interventional cardiology]

With installing a new catheterization laboratory, a quality project with focus on indications for invasive/interventional procedures was implemented. Health insurance companies as budget holders were involved in the project, external control is accomplished by their medical service (MDK). The focus on indications is new, since most approaches in this area deal with structure and/or process quality. The actual concept of this quality project makes medical performance transparent with regard to adequate indication as the first and important step to excellent quality of results. Further, the concept contains a rational approach to the controversial discussion about the increasing frequency of catheter-based coronary interventions.

[Quality control in ambulatory health care. Results of an area-wide study by the public medical service of the Baden-Württemberg health insurance]

Discussions surrounding the quality of nursing care, fueled by recurring press reports, prompted the State Nursing Insurance Associations in Baden-Wuerttemberg to request the Health Insurance Medical Service to perform a quality control of outpatient nursing care services in the state. Based on a coordinated concept and for the first time in the Federal Republic of Germany, all authorized ambulatory institutions area-wide were subjected to a uniform assessment (total survey) during an official inquiry time period. The end results of these controls failed to verify the judgement often propagated by the press based on individual cases that high-quality nursing care can no longer be afforded under the present circumstances. On the average, 55% of the personnel provided to patients by outpatient nursing services were health care professionals. What is more, this professional staff rendered 75% of all nursing care services. The evaluation of the accompanied medical visits indicated that the vast majority attempted to take active nursing care into account. With regard to quality assurance, a great optimisation potential was indicated primarily in the area of nursing documentation. Only in about 35% of the nursing documents inspected was the nursing procedure always clearly evident. A future problem could arise from the fact that of all nursing professionals with leadership responsibilities, at the time of the survey only about 37% had completed the requisite professional training qualification programme of 460 training hours. If the time before the interim deadline (March 31, 2002) is not utilised, the institutions in question could face consequences that could threaten their very existence. It is evident that a large number of outpatient nursing care services in the state of Baden-Wuerttemberg do not have their economic foundation in the domain of the Nursing Care Insurance Law, which affects both patient structure and care intensity. As a consequence, there is no quality control or inspection whatsoever for the majority of nursing care services rendered by ambulatory nursing care services at present because they are not under the jurisdiction of the German Federal Social Legislation SGB XI.

Ifosfamide and mesna: effects on the Na/H exchanger activity in renal epithelial cells in culture (LLC-PK1)

Ifosfamide (IF) is an alkylating cytostatic with urotoxic and tubulotoxic side effects which may result in the development of Fanconi syndrome in children. While the urotoxicity of IF is effectively prevented by the uroprotective thiol compound sodium-2-mercaptoethanesulfonate (Mesna), tubulo-toxicity of IF may occur even in the presence of Mesna and in the absence of any signs of urotoxicity. Using the renal tubular cell line LLC-PK1, we investigated whether there is a protective effect of Mesna or of its major dimeric metabolite Dimesna against metabolites of IF with respect to the Na/H exchanger activity. We tested the major IF metabolites 4-hydroperoxy-IF (4-OOH-IF), chloroacetaldehyde (CAA), and acrolein. All metabolites significantly inhibit the Na/H exchanger activity. Half-maximal inhibition of transport occurs at concentrations of 120 mumol/l (4-OOH-IF), 80 (CAA), and 60 mumol/l (acrolein) after 2 h of incubation. The onset of the inhibitory effect of all three metabolites is rapid. Complete inhibition of Na/H exchange by acrolein and CAA is present after a 6-hour exposure to 100 mumol/l of the respective metabolite, while 100 mumol/l 4-OOH-IF causes only 50% inhibition after 24 h of incubation. Dimesna, which the proximal tubular cell has to reduce to Mesna at the expense of intracellular glutathione before it exerts a uroprotective effect, has no protective effect in LLC-PK1 cells. Dimesna (0.3 mmol/l) displaces the dose-response curve for acrolein to the left, indicating an increased toxicity of the combination of acrolein plus Dimesna. Mesna (0.3 mmol/l) has a complete protective effect with respect to acrolein and CAA, while the protective effect versus 100 mumol/l of 4-OOH-IF is incomplete. We conclude that the function of the Na/H exchanger in LLC-PK1 cells is altered by metabolites of IF. The incomplete protection against the toxic effect of 4-OOH-IF by Mesna may explain the pathomechanism by which IF causes tubulotoxicity in the absence of urotoxicity.

Effects of cell differentiation on ion conductances and membrane voltage in LLC-PK1 cells

LLC-PK1 cells serve as a widely used model for the renal proximal tubule. Until now, little has been found out about their membrane voltage (Vm) and ionic conductances (g). Several studies have shown changes in cell properties during differentiation and ageing. The aim of this study was to examine the relationship between Vm or g and the age of these cells. Therefore, we investigated single cells, subconfluent and confluent monolayers of LLC-PK1 cells aged 1-8 days with the slow-whole-cell patch-clamp technique. The Vm of all cells was -34 +/- 2 mV (n = 75) and the membrane conductance (gm) was 2.3 +/- 0.3 nS (n = 30). Vm in cells aged up to 2 days was -24 +/- 3 mV (n = 22) whereas Vm in cells aged 5-8 days was -50 +/- 3 mV (n = 15). An increase of extracellular K+ from 3.6 to 18.6 mmol/l led to a depolarization in all cells of 4 +/- 1 mV (n = 31) and an increase of gm by 17 +/- 13% (n = 15). Complete replacement of extracellular Na+ by N-methyl-D-glucamine (NMDG) led to a hyperpolarization of 19 +/- 2 mV (n = 38) and gm was lowered by 27 +/- 14% (n = 17). A reduction in extracellular Cl- from 147 to 32 mmol/l showed no significant effect on Vm (n = 16) or gm (n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)

Dithio-bis-mercaptoethanesulphonate (DIMESNA) does not prevent cellular damage by metabolites of ifosfamide and cyclophosphamide in LLC-PK1 cells

Ifosfamide (IF) is an alkylating cytostatic with urotoxic (haemorrhagic cystitis) and nephrotoxic (Fanconi syndrome) side effects. Cyclophosphamide (CP), a structural isomer of IF, shows urotoxic but no nephrotoxic side effects. The development of haemorrhagic cystitis during therapy with IF or CP can be prevented by the uroprotective drug sodium-2-mercaptoethanesulphonate (MESNA). However, even in the presence of MESNA, Fanconi syndrome may still develop after therapy with IF. Using the renal tubular cell line LLC-PK1, we investigated whether there is a protective effect of either MESNA or of its major metabolite DIMESNA, in combination with metabolites of IF or CP, on thymidine incorporation, uridine incorporation or total protein. DIMESNA, the dimer of MESNA, is the dominant form of the molecule in the circulation; the proximal tubular cell must convert this back to MESNA at the expense of glutathione, before it can exert its uroprotective action. We did not find a protective effect of DIMESNA under any of the experimental conditions tested. LLC-PK1 cells exposed to 3 mmol/l DIMESNA did not convert DIMESNA to MESNA. The toxic effect of the CP metabolite 4-OOH-CP was more pronounced in the presence of DIMESNA than in its absence. MESNA completely prevented the toxic effects of acrolein and of 4-OOH-CP. The toxic effects of 4-OOH-IF and of chloracetaldehyde, two major metabolites of IF, were significantly reduced in the presence of MESNA. However, even at 30-fold molar excess of MESNA over a 4-OOH_IF, thymidine incorporation remained reduced by 40% compared with controls, indicating incomplete protection of tubular cells against metabolites of IF. Similarly, the effect of chloracetaldehyde was not completely reversed by MESNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity of ifosfamide, cyclophosphamide and their metabolites in renal tubular cells in culture

Ifosfamide (IF) and cyclophosphamide (CP) are highly effective alkylating cytostatic drugs. IF and CP have to be activated through a metabolic step in vivo; numerous metabolites are known. While both IF and its structural isomer CP have severe urotoxic side effects, only IF is also a nephrotoxic drug, causing tubular damage resulting in Fanconi syndrome in some cases. Little information is available regarding the pathogenic mechanism of tubular damage by IF. We used the renal epithelial cell line LLC-PK1, which has many properties of the proximal tubule, in order to investigate the toxicity of IF and CP and of their reactive metabolites 4-hydroxy-IF (4-OH-IF), 4-hydroxy-CP (4-OH-CP), acrolein and chloroacetaldehyde (CAA). Protein content of monolayers, DNA and RNA synthesis were determined by standard techniques (thymidine and uridine incorporation). IF and CP had the lowest toxicities of all compounds tested. Both drugs inhibited thymidine incorporation by about 30% at a concentration of 300 mumol/l after 1 h incubation. 4-OH-IF and 4-OH-CP were significantly more toxic than the parent drugs. Thymidine incorporation, the most sensitive parameter, was reduced by about 70% by 300 mumol/l of either compound. In addition, 4-OH-CP reduced the total protein content of monolayers. 4-OH-IF did not effect protein content and RNA synthesis. Acrolein, the most toxic metabolite tested, reduced all three parameters significantly at concentrations of 50-75 mumol/l after 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ifosfamide metabolites on sodium-dependent phosphate transport in a model of proximal tubular cells (LLC-PK1) in culture

Ifosfamide (IF) is an alkylating cytostatic drug with urotoxic (hemorrhagic cystitis) and nephrotoxic side effects. Several cases of Fanconi syndrome in children following therapy with IF were reported. Little information is available concerning the pathomechanisms of transport inhibition by IF. We used a permanent renal epithelial cell line with proximal tubular characteristics (LLC-PK1) in order to investigate the effects of IF and some of its major metabolites (4-OH-IF, chloracetaldehyde, and acrolein). LLC-PK1 cells were used in a confluent state. Sodium-dependent and sodium-independent fluxes of 32PO4 were determined by standard techniques. Activities of marker enzymes of apical and basolateral membranes, of mitochondria, and of endoplasmic reticulum were determined in cell homogenates. IF induces a moderate stimulation of PO4 transport. 4-OH-IF also has a stimulatory effect on transport at low concentrations (up to 200 mumol/l) and with short incubation (2h), while a 24-hour exposure of cells to 100 mumol/l of 4-OH-IF has an inhibitory effect of PO4 transport. Concentrations of 4-OH-IF which inhibit transport also reduce the activity of Na(+)-K(+)-ATPase. Chloracetaldehyde, like 4-OH-IF, induces a biphasic response of PO4 transport with stimulation in the low concentration range (up to 75 mumol/l) and inhibition at higher concentrations. Chloracetaldehyde reduces the activity of succinate-cytochrome c oxidoreductase, suggesting that a defect in ATP generation might play a role in the pathogenesis of Fanconi syndrome induced by IF. Acrolein strongly damages monolayers and reduces sodium-dependent transport of PO4 to very low levels at 150 mumol/l. It reduces the activities of both Na(+)-K+ ATPase and succinate-cytochrome c oxidoreductase. Acrolein also is the only metabolite with a moderate effect on alkaline phosphatase. We conclude that sodium-dependent transport of PO4 is highly sensitive to IF metabolites. In addition to direct toxic effects of IF metabolites on transport proteins within the apical plasma membrane, damage to mitochondrial enzymes and to Na(+)-K+ ATPase which generates the electrochemical gradients for secondary active PO4 transport may play an important role in the pathogenesis of Fanconi syndrome induced by IF.

Inhibition of sodium-dependent transport systems in LLC-PK1 cells by metabolites of ifosfamide

Ifosfamide (IF) is an alkylating cytostatic derived from nitrogen mustard. In addition to its well-known urotoxic effects (hemorrhagic cystitis), several cases of Fanconi syndrome following IF therapy have been reported. No information is available concerning the pathomechanisms of this tubulotoxicity. We used the permanent renal epithelial cell line LLC-PK1 in order to investigate whether major metabolites of IF (i.e. 4-OH-IF, acrolein and chloracetyldehyde) induced the transport defects most frequently detected after IF therapy in vivo. LLC-PK1 cells of passages 162-177, grown in plastic culture dishes, were used in a confluent state. Sodium-dependent and independent fluxes of l-[3H]alanine and of D-[3H]glucose were determined by standard techniques. Activities of marker enzymes of apical and basolateral membranes, of mitochondria and of endoplasmic reticulum were determined in cell homogenates. IF itself has no detectable effect on fluxes of l-alanine and D-glucose in LLC-PK1 cells. The IF metabolite 4-OOH-IF induces a clear inhibition of sodium-dependent fluxes of both substrates after a 24-hour exposure of cells to 100 mumol/l of 4-OOH-IF. Chloracetaldehyde induces a biphasic response of sodium-dependent fluxes of l-alanine with increased uptake rates at low concentrations (< 200 mumol/l) and with a short incubation time, while higher concentrations and long exposure of the cells leads to a reduction in sodium coupled transport. Glucose transport is affected in a comparable way, however, in contrast to alanine transport, chloracetaldehyde also stimulates sodium-independent fluxes of glucose. Acrolein is the most toxic substance tested. It severely damages cell monolayers at concentrations beyond 75 mumol/l. Sodium-coupled glucose and alanine transport is inhibited by acrolein at concentrations higher than 50 mumol/l. Sodium-coupled glucose transport is more sensitive to all metabolites tested than alanine transport. While acrolein strongly affects both transport systems, marker enzymes of the apical plasma membrane, i.e. alkaline phosphatase and leucine amino-peptidase, are not significantly inhibited, suggesting a specificity of the toxic effect for the transport proteins. We conclude that LLC-PK1 cells represent a good model for further investigation of the pathogenesis of Fanconi syndrome after IF therapy. Sodium-dependent transport systems are more sensitive to acrolein than other cell surface proteins.

Renal epithelial cell growth can occur in absence of Na+-H+ exchanger activity

An electroneutral Na+-H+ exchange system has been described in a variety of tissues and cell types, including those of renal origin, and has been proposed to play a role in the activation of growth. We have recently characterized the presence of this ubiquitous transporter in the apical domain of confluent epithelial LLC-PK1 cells (J. Biol. Chem. 261: 3252-3258, 1986). Because most apical membrane proteins appear late in cell growth, accompanying epithelial cell polarization, we determined whether the Na+-H+ exchanger is required for the growth of LLC-PK1 cells. The studies reported here show that there is no obligatory requirement for increased H+ efflux or Na+ entry via the Na+-H+ exchanger for the initiation of cell growth in this epithelial cell line. We used 22Na+ influx, acid extrusion, and intracellular pH determinations to show that onset of cell growth, as measured by DNA content, precedes the activity of the Na+-H+ exchanger in exponentially growing cells, whereas confluent monolayers express Na+-H+ exchanger activity. When confluent cells are replated at low density, Na+-H+ exchanger activity disappears within 8 h in contrast to high-density replated cells. The fact that Na+-H+ exchanger activity is only present in confluent monolayers suggests that the development of tight junctions and polar differentiation play a role in the expression of the Na+-H+ exchanger and that this exchanger is more important to the polar epithelial cell for transepithelial transport than for the maintenance of intracellular pH.

Inhibition of epithelial Na+ transport by atriopeptin, protein kinase c, and pertussis toxin

We have recently shown the selective inhibition of an amiloride-sensitive, conductive pathway for Na+ by atrial natriuretic peptide and 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) in the renal epithelial cell line, LLC-PK1. Using 22Na+ fluxes, we further investigated the modulation of Na+ transport by atrial natriuretic peptide and by agents that increase cGMP production, activate protein kinase c, or modulate guanine nucleotide regulatory protein function. Sodium nitroprusside increases intracellular cGMP concentrations without affecting cAMP concentrations and completely inhibits amiloride-sensitive Na+ uptake in a time- and concentration-dependent manner. In contrast, 8-BrcAMP is without effect on Na+ uptake through the Na+ channel. 1-Oleoyl 2-acetylglycerol (10 micrograms/ml) and phorbol 12-myristate 13-acetate (100 nM), activators of protein kinase c, inhibit Na+ uptake by 93 +/- 13 and 51 +/- 10%, respectively. Prolonged incubation with phorbol ester results in the downregulation of protein kinase c activity and reduces the inhibitory effect of atrial natriuretic peptide, suggesting that the action of this peptide involves stimulation of protein kinase c. Pertussis toxin, which induces the ADP-ribosylation of a 41-kDa guanine nucleotide regulatory protein in LLC-PK1 cells, inhibits 22Na+ influx to the same extent as amiloride. Thus, increasing cGMP, activating protein kinase c, and ADP-ribosylating a guanine nucleotide regulatory protein all inhibit Na+ uptake. These events may be sequentially involved in the action of atrial natriuretic peptide.

Phosphate transport in brush-border membranes from control and rachitic pig kidney and small intestine

1. Na-Pi co-transport was analysed using renal cortical and small intestinal brush-border membrane vesicles which were isolated from control (normal, heterozygotes) and rachitic piglets (homozygotes). 2. A kinetic analysis of Na-dependent initial linear uptake of Pi was performed using vesicles obtained from control animals. The results suggest similar kinetic properties for the renal and small intestinal co-transport system. (i) A sigmoidal dependence on Na concentration of Pi uptake suggests the involvement of more than one Na ion in the co-transport. (ii) Increasing Na concentration leads to an increase in the apparent affinity of the transport system for Pi and has minimal effect on the apparent Vmax (maximum velocity of uptake). (iii) Increasing pH leads to an increase in Pi transport rate. 3. The kinetic characteristics of the Na-Pi co-transport system in vesicles obtained from rachitic animals were similar to those in controls. The apparent Vmax, but not the apparent Km (Michaelis constant) for Na and Pi, is reduced in intestinal and renal brush-border membranes isolated from rachitic animals as compared to control animals. Injection of vitamin D3, three days prior to killing of rachitic litter-mates, increased the Na-Pi uptake rate in the brush-border membrane vesicles isolated from these piglets. 4. It is concluded that intestinal and renal brush-border membranes from piglets contain a similar Na-Pi co-transport system and that in vitamin-D-dependent rickets the number of operating transport units is reduced in both membranes.

Stimulation of Na+/phosphate cotransport in LLC-PK1 cells by 12-O-tetradecanoylphorbol 13-acetate (TPA)

We have tested for the effect of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) on Na+/phosphate cotransport in an established epithelial cell line of renal origin (LLC-PK1). Incubation of LLC-PK1 cells with TPA produced an increase in Na+/phosphate (Pi) cotransport. The maximal response was reached at a TPA concentration of 10 ng/ml. Other phorbol esters which have no potency or a smaller one to activate protein kinase C had no effect on Na+/Pi cotransport. Incubation of LLC-PK1 cells with 10 ng/ml TPA for 8 h led to a 300% increase in Na+/Pi cotransport; in the presence of cycloheximide the increase amounted only to a 100% and was reached within 2 h. Kinetic analysis of Na+/Pi cotransport indicated an increase in the apparent Vmax without an effect on the apparent Km. The increased Pi transport was retained in isolated apical vesicles. Na+-dependent alanine transport into LLC-PK1 monolayers was affected by TPA administration in a similar manner. TPA had under the chosen experimental conditions no effect on [3H]thymidine incorporation into DNA excluding a general proliferative effect. We conclude that TPA via activation of protein kinase C regulates the number of operating transport systems. As also other Na+-coupled transport systems are influenced, the TPA effect appears to be related to the expression of a general 'adaptive' alteration of membrane transport in LLC-PK1 cells.

Sodium-dependent transport of Pi by an established intestinal epithelial cell line (CaCo-2)

The uptake of inorganic phosphate (Pi) was analyzed in monolayers and in apical membrane vesicles (AMV) of the established intestinal cell line CaCo-2. AMV, prepared by a MgCl2 precipitation technique, were enriched approximately 10-fold in alkaline phosphatase activity. Pi uptake into intact cells as well as into AMV was specifically dependent on the presence of sodium. In the presence of high sodium concentrations, the apparent Km for Pi was 214 +/- 17 mumol/l in monolayers and 300 +/- 19.7 mumol/l in AMV. Increasing the sodium concentration increased the apparent affinity of the transport system for Pi but hardly affected the maximal velocity (Vmax). At 0.1 mmol/l Pi and pH 7.4, the apparent Km for sodium was approximately 70 mmol/l in intact cells as well as in AMV. The results obtained in both systems suggested the involvement of two sodium ions and one phosphate ion in the transport process. Advancing confluence--independently of the age of the monolayers--reduced sodium-dependent uptake of Pi significantly by a decrease in Vmax, whereas the apparent Km for Pi remained unchanged. It is concluded that the apical membrane of CaCo-2 cells contains a sodium-dependent transport system for Pi.

Effect of pH on phosphate transport in rat renal brush border membrane vesicles

The initial linear rate of phosphate uptake was analyzed in rat renal brush border membrane vesicles. An increase in medium pH from 6.0 to 8.0 increased the sodium gradient-dependent phosphate uptake about 20-fold. Sodium-independent phosphate uptake was not altered in this pH range. At pH 7.4 an intravesicular acid pH stimulated the initial linear uptake rate (20-25%). The apparent Km for sodium increased from about 100 to 200 mM when pH was decreased from 7.4 to 6.4. The Hill coefficient for sodium interaction was close to 2 and was unaffected by pH. Increasing external sodium reduced the apparent Km of the transport system for phosphate independent of pH. Variations of phosphate concentration had no influence on the apparent Km for sodium. At high sodium concentrations, small effects (20-30%) of pH on the apparent Vmax of the transport system were found; measured at saturating sodium concentrations, the apparent Km values calculated on the basis of total phosphate were increased (50-60%) when pH was decreased from 7.4 to 6.4. The data indicate that the major effect of pH is to modify the interaction of the transport system with sodium. At nonsaturating sodium concentrations, this resulted indirectly in a reduction in the affinity for phosphate related to a different occupancy of the sodium binding site. The differences of transport rate at low phosphate and high sodium concentrations could be explained by preferential transport of divalent phosphate as well as by pH effects on other carrier properties.

Renal interstitial pressure and sodium excretion during hilar lymphatic ligation

Because lymphatic vessels drain the cortical interstitium of the kidney, lymphatic drainage might modulate cortical interstitial pressure and tubular Na+ reabsorption. We investigated the effects of short-term hilar lymph duct ligation in the rat on renal interstitial hydraulic pressure (assessed from subcapsular pressure), tubular Na+ reabsorption, and renal hemodynamics in the basal state and during volume expansion with saline. Subcapsular pressure was higher in lymphatic-ligated than in sham-operated kidneys both in the basal state (5.9 +/- 0.3 vs. 2.1 +/- 0.3 mmHg) and during short-term volume expansion (8.4 +/- 0.7 vs. 3.5 +/- 0.3). Compared with contralateral control kidneys, lymphatic ligation increased the basal urine flow (V) (1.76 +/- 0.2 vs. 1.18 +/- 0.2 microliter X min-1 X 100 g-1) and urinary Na+ excretion (UNaV) (0.10 +/- 0.03 vs. 0.05 +/- 0.02 mumol X min-1 X 100 g-1), but urea excretion, osmolar clearance, glomerular filtration rate, renal plasma flow, and filtration fraction were unchanged. The increases in V and UNaV with lymphatic ligation were not seen in salt-depleted rats but both were augmented by short-term volume expansion with saline. Sympathetic activation and inhibition by carotid occlusion and ganglionic blockade, respectively, elicited the same changes in vascular resistance in lymphatic-ligated and control kidneys. In conclusion, 1) lymphatic drainage is required to maintain a low renal cortical interstitial hydraulic pressure; 2) lymphatic ligation decreases Na+ and fluid reabsorption; 3) the natriuretic and diuretic effects of lymphatic ligation are not due to major changes in renal innervation or renal hemodynamics or to changes in osmolar or urea excretion but depend on the degree of extracellular fluid volume expansion.