PP2ARts1 antagonizes Rck2-mediated hyperosmotic stress signaling in yeast.

In Saccharomyces cerevisiae, impairment of protein phosphatase PP2ARts1 leads to temperature and hyperosmotic stress sensitivity, yet the underlying mechanism and the scope of action of the phosphatase in the stress response remain elusive. Using a quantitative mass spectrometry-based approach we have identified a set of putative substrate proteins that show both hyperosmotic stress- and PP2ARts1-dependent changes in their phosphorylation pattern. A comparative analysis with published MS-shotgun data revealed that the phosphorylation status of many of these sites is regulated by the MAPKAP kinase Rck2, suggesting that the phosphatase antagonizes Rck2 signaling. Detailed gel mobility shift assays and protein-protein interaction analysis strongly indicate that Rck2 activity is directly regulated by PP2ARts1 via a SLiM B56-family interaction motif, revealing how PP2ARts1 influences the response to hyperosmotic stress in Yeast.

Hyponatremia - A rare complication of Gitelman's syndrome.

Gitelman's syndrome (GS) is a rare autosomal recessive disorder caused by mutations in thiazide-sensitive NaCl cotransporter. We report a 49-year-old, normotensive lady with prolonged hypokalemia since her 20s who was diagnosed with GS at our renal clinic. During follow-up, she was found to have mild, asymptomatic, euvolemic hyponatremia with low serum uric acid, inappropriately high urine osmolality and sodium consistent with syndrome of inappropriate antidiuretic hormone-like presentation. Despite life-long urinary sodium losses, hyponatremia has rarely been reported in GS to be due to the primary disease process. We present relevant clinical data and hypothesize on why this disease per se may be a risk factor for dilutional hyponatremia.

Successful maternal and fetal outcome in a kidney transplant patient with everolimus exposure throughout pregnancy: a case report.

Pregnancy after kidney transplantation is becoming more common as more patients of childbearing age are undergoing successful transplantation. There is limited evidence on the safety and efficacy of mammalian target of rapamycin inhibitors during pregnancy, which are considered Category C. We will review the use of this class of medications in pregnancy, which is currently contraindicated due to risk of fetal complications. We will also present the case of a successful pregnancy and renal outcome in a 33-year-old kidney transplant recipient who was administered everolimus throughout pregnancy.

Activation of the G2/M-specific gene CLB2 requires multiple cell cycle signals.

In budding yeast (Saccharomyces cerevisiae), the periodic expression of the G2/M-specific gene CLB2 depends on a DNA binding complex that mediates its repression during G1 and activation from the S phase to the exit of mitosis. The switch from low to high expression levels depends on the transcriptional activator Ndd1. We show that the inactivation of the Sin3 histone deacetylase complex bypasses the essential role of Ndd1 in cell cycle progression. Sin3 and its catalytic subunit Rpd3 associate with the CLB2 promoter during the G1 phase of the cell cycle. Both proteins dissociate from the promoter at the onset of the S phase and reassociate during G2 phase. Sin3 removal coincides with a transient increase in histone H4 acetylation followed by the expulsion of at least one nucleosome from the promoter region. Whereas the first step depends on Cdc28/Cln1 activity, Ndd1 function is required for the second step. Since the removal of Sin3 is independent of Ndd1 recruitment and Cdc28/Clb activity it represents a unique regulatory step which is distinct from transcriptional activation.

High prevalence of alcoholism in dialysis patients.

Alcoholism is one of the most common psychosocial disorders, affecting approximately 10% of the general population. The impact of alcoholism on the care of patients with other medical illnesses has not been addressed in many of these populations, including patients with end-stage renal disease (ESRD) undergoing hemodialysis. We set out to determine the prevalence of alcoholism in an urban hemodialysis population and ascertain whether alcoholism had an effect on compliance in this population. One hundred sixty-three urban hemodialysis patients were screened using the Michigan Alcoholism Screening Test (MAST), a 25-item questionnaire that has been validated in multiple trials. Forty-five patients (27.6%) scored 5 or greater on the MAST. The MAST-positive subjects were younger (age, 55 +/- 15 years versus 64 +/- 13 years) and tended to be men (58% versus 43%). There was no significant difference in the incidence of diabetic kidney disease; however, there were significantly more human immunodeficiency virus (HIV)-positive patients in the MAST-positive group. The dietary compliance measures of predialysis potassium or phosphorus levels did not differ between the two groups. A trend toward lower serum albumin level was evident in the men in the MAST-positive group (3.75 +/- 0.57 versus 3.91 +/- 0.30 g/dL; P = 0.0212). In conclusion, there is a high prevalence of alcoholism in the urban dialysis population. Alcoholic patients with ESRD are younger and tend to be men. HIV-positive patients with ESRD have a high prevalence of concomitant alcoholism. Compliance indicators of predialysis potassium and phosphorus levels are not affected. However, nutritional status, measured by serum albumin level, tends to be poorer in the alcoholic group.

Multiple measurements of depression predict mortality in a longitudinal study of chronic hemodialysis outpatients.

BACKGROUND: The medical risk factors associated with increased mortality in hemodialysis (HD) patients are well known, but the psychosocial factors that may affect outcome have not been clearly defined. One key psychosocial factor, depression, has been considered a predictor of mortality, but previous studies have provided equivocal results regarding the association. We sought to determine whether depressive affect is associated with mortality in a longitudinal study of end-stage renal disease (ESRD) patients treated with HD, using multiple assessments over time. METHODS: Two hundred ninety-five outpatients with ESRD treated with HD were recruited from three outpatient dialysis units in Washington D.C. to participate in a prospective cohort study with longitudinal follow-up. Patients were assessed every six months for up to two years using the Beck Depression Inventory (BDI), age, serum albumin concentration, Kt/V, and protein catabolic rate (PCR). A severity index, previously demonstrated to be a mortality marker, was used to grade medical comorbidity. The type of dialyzer with which the patient was treated was noted. Patient mortality status was tracked for a minimum of 20 and a maximum of 60 months after the first interview. Cox proportional hazards models, treating depression scores as time-varying covariates in a univariable analysis, and controlling for age, medical comorbidity, albumin concentration, and dialyzer type and site in multivariable models, were used to assess the relative mortality risk. RESULTS: The mean (+/- SD) age of our population at initial interview was 54.6 +/- 14.1 years. The mean PCR was 1.06 +/- 0.27 g/kg/day, and the mean Kt/V was 1.2 +/- 0.4 at baseline, suggesting that the patients were well nourished and dialyzed comparably to contemporary U.S. patients. The patients' mean BDI at enrollment was 11.4 +/- 8.1, in the range of mild depression. Patients' baseline level of depression was not a significant predictor of mortality at 38.6 months of follow-up. In contrast, when depression was treated as a time-varying covariate based on periodic follow-up assessments, the level of depressive affect was significantly associated with mortality in both single variable and multivariable analyses. CONCLUSIONS: Higher levels of depressive affect in ESRD patients treated with HD are associated with increased mortality. The effects of depression on patient survival are of the same order of magnitude as medical risk factors. Our findings using both controls for factors possibly confounded with depressive affect in patients with ESRD and time-varying covariate analyses may explain the inconsistent results of previous studies of depression and mortality in ESRD patients. Time-varying analyses in longitudinal studies may add power to defining and sensitivity to establishing the association of psychosocial factors and survival in ESRD patients. The mechanism underlying the relationship of depression and survival and the effect of interventions to improve depression in HD outpatients and general medical inpatients should be studied.

Interdialytic weight gain and survival in hemodialysis patients: effects of duration of ESRD and diabetes mellitus.

BACKGROUND: Medical mortality determinants in end-stage renal disease (ESRD) patients treated with hemodialysis (HD) are well known. More recently, associations have been established between the dose of dialysis administered and patient survival. We showed in a prospective study that both dialyzer type and patient compliance with the dialysis prescription were independently associated with survival. Although several parameters of dialytic technique and patient compliance are associated with differential survival in patients with ESRD treated with HD, the association of interdialytic weight gain (IWG) with survival is unclear. No study has assessed the relationship between IWG and mortality in HD patients, controlled for multiple medical risk factors. The aim of our study was to determine whether IWG was associated with survival in patients with ESRD treated with HD, controlling for multiple medical and dialytic risk factors. METHODS: We prospectively conducted an observational, longitudinal, multicenter study of 283 urban HD patients to determine the relationship of IWG with several dialytic parameters and patient survival. Medical risk factors such as demographic indices and comorbid conditions were assessed. We studied Kt/V, the protein catabolic rate (PCR), serum albumin and anthropometric measurements, behavioral compliance indices, dialyzer characteristics, and serum electrolyte concentrations, and correlated these with IWG. In addition, the duration of dialysis was assessed in HD patients with and without diabetes mellitus. Cox proportional hazards models assessed the relative mortality risk of increased IWG, controlling for variations in medical comorbidity and other mortality determinants. RESULTS: The mean (+/- SD) age of our population was 54.6 +/- 14.1 years, and the mean time they were treated with HD was 30.4 +/- 46.9 months. The mean IWG was 1.54 +/- 0.71% dry wt/day. Correlations were found between increased IWG and younger age, and lower midarm circumference, and increased Kt/V, PCR, and serum potassium concentration. The mean follow-up period was 48.9 +/- 10.6 months. An increase in IWG was associated with a significantly increased relative mortality risk in diabetic ESRD patients treated with HD when variations in age, comorbidity, serum albumin concentration, and dialyzer type and site were controlled. There was, however, no association of increased mortality risk with increased IWG in the larger population of patients without diabetes. In further analyses, the increased mortality risk associated with increased IWG was found to be present only in patients with diabetes mellitus who had recently started HD therapy for ESRD. CONCLUSION: IWG is correlated with several nutritional and dialytic variables and with parameters that predict survival in HD patients. Increased IWG is independently associated with decreased survival of diabetic ESRD patients treated with HD, after adjusting for variation in other medical risk factors. The population of incident diabetic HD patients is particularly susceptible to increased risk associated with increased IWG. The mechanisms underlying these results are obscure, but IWG might be associated with poorer survival in this population if it were linked to worsened hypertension, cardiovascular stress, or poorer glycemic control. Interventions to improve compliance with IWG in incident diabetic HD patients are warranted.

Psychosocial factors, behavioral compliance and survival in urban hemodialysis patients.

BACKGROUND: The medical risk factors associated with increased mortality in hemodialysis (HD) patients are well known, but the psychosocial factors that may affect outcome have not been clearly defined. Psychosocial factors could affect mortality through interaction with parents' nutrition or their compliance with the dialysis prescription. We conducted a prospective, longitudinal, multicenter study of urban HD patients to determine the contribution of compliance and psychosocial factors to patient survival. METHODS: Patients were assessed using indices of social support, patient's assessments of their well-being, including illness effects (IEQ), and satisfaction with life (SWLS), the Beck Depression Inventory (BDI), serum albumin concentration, Kt/V and protein catabolic rate (PCR). Behavioral compliance was measured three ways: percent time actually dialyzed per treatment compared to prescribed time (shortening behavior); percent sessions attended (skipping behavior) and total integrated time compliance (% TCOMP). A severity index, previously demonstrated to be a mortality marker, was used to grade medical comorbidity. The typed of dialyzer the patient was treated with was noted. A Cox proportional hazards model, controlling for age, medical comorbidity, albumin concentration and dialyzer type was used to assess relative mortality risk of variations in psychosocial factors and behavioral compliance. RESULTS: A total of 295 patients (60.8% of those eligible) agreed to participate. The mean ( +/- SD) age of our population was 54.6 +/- 14.1 year, mean PCR was 1.06 +/- 0.27 g/kg/day, and mean Kt/V 1.2 +/- 0.4, suggesting the patients were well nourished and adequately dialyzed. The patients' mean BDI was 11.4 +/- 8.1 (in the range of mild depression). Patients' SWLS was similar to that of a group of patients without chronic illness. After a 26 month mean follow-up period, higher levels of perceived social support, improved perception of the effects of illness and increased behavioral compliance were significantly associated with decreased relative mortality risk (0.8, 0.77, and 0.79, respectively), controlled for variations in patients' age, severity of illness, serum albumin concentration and dialyzer type. Variations in depression and Kt/V were not predictors of mortality during the observation period. CONCLUSIONS: Lower levels of social support, decreased behavioral compliance with the dialysis prescription, and increased negative perception of the effects of illness are independently associated with increased mortality in ESRD patients treated with HD. The effects are of the same order of magnitude as medical risk factors. Such effects may be attributable to a relationship between a patients' perception of social support and effects of illness and behavior, with other factors such as the provision of better medical care in patients with larger social networks. The mechanism underlying the relationship of psychosocial factors and compliance and survival, and the effect of interventions to improve perception of illness, and increase social support and compliance with the dialysis prescription in HD patients should be studied.

Immunologic function and survival in hemodialysis patients.

BACKGROUND: Although the medical determinants of mortality in patients with end-stage renal disease (ESRD) treated with hemodialysis (HD) are well appreciated, the contribution of immunologic parameters to survival in such patients is unclear, especially when variations in age, medical comorbidity and nutrition are controlled. In addition, although dysregulation of cytokine metabolism has been appreciated in patients with ESRD, the association of these parameters with outcomes has not been established. Recently, the type of dialyzer used in patients' treatment has been associated with survival, but the mechanisms underlying these findings, including their immune effects, have not been established. We conducted a prospective, cross-sectional, observational multicenter study of urban HD patients to determine the contribution of immunological factors to patient survival. We hypothesized increased proinflammatory cytokines would be associated with increased mortality, and that improved immune function would be associated with survival. METHODS: Patients were assessed using demographic and anthropometric indices, Kt/V, protein catabolic rate (PCR) and immunologic variables including circulating cytokine [interleukin (IL)-1, IL-2, IL-4, IL-5, IL-6, IL-12, IL-13 and tumor necrosis factor (TNF)-alpha] levels, total hemolytic complement activity (CH50), and T cell number and function. A severity index, previously demonstrated to be a mortality marker, was used to grade medical comorbidity. A Cox proportional hazards model, controlling for patients' age, severity index, level of serum albumin concentration, dialyzer type and dialysis site was used to asses relative survival risk. RESULTS: Two hundred and thirty patients entered the study. The mean (+/- SD) age of the population was 54.4 +/- 14.2 years, mean serum albumin concentration was 3.86 +/- 0.47 g/dl, mean PCR was 1.1 +/- 0.28 g/kg/day, and mean Kt/V 1.2 +/- 0.3. Patients' serum albumin concentration was correlated with levels of Kt/V and PCR, and their circulating IL-13 and TNF-alpha levels, but negatively with their circulating IL-2 levels, T-cell number and T-cell antigen recall function. T-cell antigen recall function correlated negatively with PCR, but not Kt/V. There was no correlation of any other immune parameter and medical or demographic factor. Immune parameters, were all highly intercorrelated. Mean level of circulating cytokines in HD patients were in all cases greater than those of a normal control group. There were few differences in medical risk factors or immune parameters between patients treated with different types of dialyzers. After an almost three-year mean follow-up period, increased IL-1, TNF-alpha, IL-6, and IL-13 levels were significantly associated with increased relative mortality risk, while higher levels of IL-2, IL-4, IL-5, IL-12, T-cell number and function, and CH50 were associated with improved survival. The difference in survival between patients treated with unmodified cellulose dialyzers and modified or synthetic dialyzers approached the level of statistical significance, but there were no differences in levels of circulating cytokines between these two groups. CONCLUSIONS: Higher levels of circulating proinflammatory cytokines are associated with mortality, while immune parameters reflecting improved T-cell function are associated with survival in ESRD patients treated with HD, independent of other medical risk factors. These factors may serve as markers for outcome. The mechanism underlying the relationship of immune function and survival, and the effect of interventions to normalize immune function in HD patients should be studied.

Biology of the mesangial cell in glomerulonephritis--role of cytokines.

The mesangial cell occupies a central position in the genesis of the pertubations occurring during the pathogenesis of glomerulonephritis. In vitro studies have shown that this cell is a metabolically active cell producing a variety of cytokines which act as autocoids; such cytokines are also liberated by the monocytes/macrophages which infiltrate the glomerulus in nephritis. This review summarizes the evidence for the participation of these cytokines in animal models of nephritis and in human renal disease, focusing on the roles of basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor-beta, colony-stimulating factor-beta, tumor necrosis factor, interleukin-1, and interleukin-6.

Psychologic functioning, quality of life, and behavioral compliance in patients beginning hemodialysis.

Psychologic and demographic characteristics have been shown to correlate with behavioral compliance in studies of prevalent hemodialysis (HD) patients. Few data, however, exist on the psychologic characteristics or their relationship to compliance in patients initiating HD treatment, or incident patients. Our previous work with prevalent HD patients showed an interrelationship among social support, perception of the effects of illness, and depression measured by a standardized depression index and a cognitive depression index deleting somatic symptoms. To compare psychosocial and behavioral compliance parameters in incident and prevalent patients, 99 incident HD patients undergoing dialysis for less than 6 months were assessed by using a variety of questionnaires. The patients' mean standardized depression index score was in the range of mild depression. There was no difference in mean age, Karnofsky functional status, perception of effects of illness or standardized or cognitive depression scores between incident patients and 149 prevalent patients treated with HD for 6 to 246 months. Satisfaction with life scores and perception of sexual adjustment were better, but Kt/V (quantitative measure of the amount of dialysis provided) and protein catabolic rate were lower in incident than in prevalent patients. Social support and perception of illness scores correlated with depression measures in incident patients, findings that were similar to prevalent patients. Incident (as did prevalent) patients showed striking bivariate correlations between the psychosocial and depression variables, but fewer correlations between psychologic and compliance measures. Both standard compliance parameters, such as mean predialysis serum phosphorus and potassium concentration, and behavioral compliance were better in incident than in prevalent patients. Worsened sexual adjustment, functional status, and increased severity of illness were correlated with improved behavioral compliance in incident patients. Behavioral compliance styles correlated with different social support and severity of medical illness variables in incident and prevalent patients, when assessed by multiple linear regression analysis. These different patterns suggest the existence of different mechanisms of adaptation in the groups. Measures focused on increasing delivery of dialysis and enhancing social support in urban African-American patients starting HD therapy may be useful in improving compliance with the dialysis prescription, and indirectly improving survival.

Antibiotic-resistant endocarditis in a hemodialysis patient.

A chronic dialysis patient developed persistent bacteremia as a result of infection with Enterococcus faecium. During the patient's illness, resistance to ampicillin, gentamicin, vancomycin, and teicoplanin developed. Despite arteriovenous (AV) graft removal and an extensive but inconclusive search for the source of the infection, bacteremia persisted. On autopsy, the patient was found to have had aortic-valve endocarditis. Endocarditis is a well-known complication in dialysis patients. Multidrug-resistant organisms are becoming more prevalent in hospitalized patients as well. Risk factors for the development of endocarditis in dialysis patients include catheters, AV grafts, and calcific valvular disease, all in conjunction with frequent access to the circulation. Avoidance of temporary catheter use by prompt placement of AV fistulas or grafts and consideration of their early use, the meticulous care of catheters once in place, and treatment of the nasal carriage of Staphylococcus aureus may lower the incidence of bacteremia and therefore endocarditis in dialysis patients. The removal of infected catheters and/or AV grafts if prompt clearing of the blood with antibiotics does not occur is the next step, followed by valve replacement in selected cases. The routine use of vancomycin in the dialysis population should be reevaluated in light of the development of high-level antibiotic-resistant organisms.

Aspects of quality of life in hemodialysis patients.

The proper means of measuring quality of life in chronically ill patients is unclear. Because different measures may assess varied aspects of patients' experience and because they may be interrelated in different ways, the relationship between several of these quality-of-life measures, including indices of psychological well-being, social support, and severity of illness in ESRD patients treated with hemodialysis (HD), was prospectively assessed. In addition, it was determined whether patients' assessment of quality of life, along any dimension, was related to patient compliance in three urban HD units, in a population largely composed of African-American patients. Severity of illness scores correlated with both attendance and compliance with the dialysis prescription. Karnofsky scores correlated inversely with age, depression, social environment, and level of severity of illness, as expected, but not with behavioral compliance measures. Social support scores correlated with perception of illness, depression, satisfaction with life, and adjustment to illness scores, but not with behavioral or standard compliance measures. Perception of illness scores correlated with depression, social support, adjustment to illness, and satisfaction with life scores, but not with Karnofsky ratings, severity scores, or standard and/or behavioral compliance measures. Social environment scores correlated with almost all assessed variables, with the exception of anthropometric measurements, predialysis phosphorus levels, and behavioral compliance measures. Satisfaction with life scores (a global, subjective measure of quality of life) correlated with advancing age, level of social support, severity of illness, and the presence of a relationship, but were not correlated with Karnofsky scores. These data suggest that quality of life in patients treated with HD must be measured in several ways. The Psychological Adjustment to Illness Scale Social Environment score may be a useful, generalizable adjunct measure of quality of life in HD patients, in addition to the Satisfaction With Life Scale. Quality of life and perception of the effects of illness are not necessarily associated with functional ability in HD patients. These findings must be considered where making decisions about the discontinuation of HD treatment.

Behavioral compliance with dialysis prescription in hemodialysis patients.

The relationship between compliance and outcome is poorly understood, partially because there has been no gold standard for measuring compliance in hemodialysis patients. To investigate interrelationships between psychological, medical, and compliance factors, hemodialysis (HD) patients were studied with the Beck Depression Inventory, and a subset, the Cognitive Depression Index, the Perception of Illness Effects scale, and the Multidimensional Scale of Perceived Social Support. Behavioral compliance was measured in three ways: (1) percent time compliance (signifying "shortening behavior"); (2) percent attendance (signifying "skipping behavior) (3) percent total time compliance, assessing patients' time on dialysis normalized for prescribed time, including all shortenings and absences. Standard compliance indicators (predialysis serum potassium and phosphorus concentrations and interdialytic weight gain) were also analyzed. The patients' mean Beck Depression Inventory was in the range of mild depression. The prevalence of depression was 25.5%. Both depression indices correlated with Perception of Illness Effects scale scores. In general, social support was related to both measures of depression and perception of illness effects. Total time compliance was 95.8 +/- 5.0%. Younger patients were more likely to skip treatments compared with older patients. Time compliance comprised a wide spectrum, with most patients relatively compliant, whereas a small proportion received far less than their prescribed dialysis. Skipping and shortening behaviors did not correlate, suggesting that these constitute two separate types of noncompliant behaviors. Time compliance parameters did not correlate with potassium levels or interdialytic weight gain, but did correlate with phosphorus levels. Interrelationships between behavioral compliance measures and other parameters varied between units and patients of different gender. Finally, behavioral compliance patterns were stable over months in patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of atrial natriuretic peptide-stimulated cGMP production in the inner medulla.

Studies were performed to examine the regulation of atrial natriuretic peptide- (ANP) stimulated guanylate cyclase in the the inner medulla. Primary cultures of rat inner medullary collecting tubular cells exposed to 10(-7) M ANP increased cGMP formation to 31.2 +/- 1.8 compared to the basal production of 2.1 +/- 0.6 fm/micrograms protein. This response did not appear to be transduced via a Gi protein, as preincubation with pertussis toxin did not alter the response to 10(-7) M ANP, and saponized cells exposed to 10 microM GTP gamma S did not enhance the response to ANP (77.3 +/- 5.9 vs. 86.7 +/- 6.3 g/micrograms). Likewise, changes in extracellular Ca2+ from 0.5 to 3.0 mM, decrements in intracellular Ca2+ with EGTA or increments in intracellular Ca2+ with ionomycin (5 microM) did not significantly alter the response to ANP. Neither activation of protein kinase A with forskolin (36.5 +/- 5.1) nor of protein kinase C with s,n-1,2-dioctanoylglycerol (33.2 +/- 2.5) altered the response to 10(-7) M ANP (32.2 +/- 3.3, NS). As the inner medullary environment was hypertonic, the effect of altering tonicity was studied. Cells grown for 48 hours in hypertonic media (600 mOsm/kg H2O) displayed enhanced response to 10(-8) and 10(-7) M ANP when osmolality was raised by either Na+ alone or in combination with urea, but not by urea alone. Our studies demonstrate that ANP-stimulated guanylate cyclase is insensitive to alterations in either intra- or extracellular Ca2+, is not subject to inhibition by protein kinase, and does not involve a pertussis-sensitive G protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Myo-inositol uptake by rat cultured inner medullary collecting tubule cells: effect of osmolality.

Myo-inositol (MI) is involved in the adaptation to hyperosmolality. Its uptake by rat inner medullary collecting duct (RIMCD) cells has not been studied. Compared with cells grown in isotonic media, those grown in hyperosmolality display marked enhancement in [3H]MI uptake [counts/min (cpm).microgram protein-1.2 h-1] from 217 +/- 23 to 718 +/- 64, P less than 0.001. This is mimicked by the supplementation with 300 mM mannitol (638 +/- 59, P less than 0.001) but not by 300 mM urea. The increment in [3H]MI is observed at 37 degrees C but not at 4 degrees C. MI uptake is Na+ dependent in cells grown both in hyperosmolal or isotonic media. At least 12 h of hyperosmolality are needed to enhance MI uptake, and reexposure to isotonic media for at least 24 h is required for the enhancement to reverse. The effects of the microtubular inhibitor, nocodazole (10 micrograms/ml), and the protein synthesis inhibitor, cycloheximide (30 micrograms/ml), were studied. Cells grown with nocodazole show unimpaired enhancement of MI uptake. Cycloheximide exposure (16 h) does not affect MI uptake in isotonic media (182 +/- 23 vs. 191 +/- 15), but inhibited enhanced MI uptake in hyperosmolality (822 +/- 53 in the absence vs. 331 +/- 24 in the presence of cycloheximide, P less than 0.001). We conclude that hyperosmolality stimulates the synthesis of a protein, most likely an Na-MI cotransporter, that markedly enhances MI uptake. This process may be critical to the osmoregulation of RIMCD cells.

The biology of mesangial cells in glomerulonephritis.

It is likely that a complex bidirectional interaction occurs between mesangial cells and the immune cells which infiltrate the mesangium during nephritis. Macrophages and other immune cells liberate a series of mediators, including substances such as IL-1, beta-endorphin, TNF, and PDGF--all of which promote the growth of mesangial cells. The end result is mesangial cell proliferation and increased matrix production, both of which are seen in nephritis. The proliferating mesangial cells liberate autocoids such as IL-1 and PDGF, thereby setting up an amplifying loop. Simultaneously, suppressive factors such as TGF-beta are released which antagonize the actions of these growth-promoting substances. The proliferating mesangial cells also produce immunomodulatory peptides, which will in turn act on the infiltrating macrophages to stimulate their replication and activation. Such activated macrophages continue to amplify the inflammatory lesion and also promote the phagocytosis of localized antigen-antibody complexes. The net effect of all of these interactions will depend on the dominance of substances which persist and override the roles of other molecules. Studies of the controls which regulate the production of these growth factors/immune modulators will yield insights into the fundamental mechanisms which determine the outcome in glomerulonephritis.

Effects of prostacyclin on the cAMP system in cultured rat inner medullary collecting duct cells.

Rat inner medullary collecting tubule (RIMCT) cells produce arachidonate derivatives including prostacyclin (PGI2). In RIMCT cells, PGI2 causes a dose-dependent increase in adenosine 3',5'-cyclic monophosphate (cAMP; fmol/micrograms protein) from a basal level of 15.6 +/- 1.7 to 32.4 +/- 5.7 at 0.3 microM, 63.3 +/- 8.3 at 3 microM, and 103.5 +/- 9.4 at 30 microM PGI2. At concentrations of arginine vasopressin (AVP) from 10(-7) to 10(-9) M, cAMP was greater in the presence than absence of 3 microM PGI2, suggesting independent sites of action. To assess whether the PGI2 effect is mediated by the prostaglandin E2 (PGE2) receptor, desensitization studies were performed. A 6-h preincubation with 10 microM PGE2 blunted the response to 3 microM PGE2 by 90 +/- 2% but the PGI2 response was decreased by only 31 +/- 5%, P less than 0.001. Carbaprostacyclin (carba-PGI2), a stable analogue of PGI2, blunted the cAMP response to PGI2 by 94 +/- 3% but to PGE2 by only 46 +/- 7%, P less than 0.005. The postreceptor effect of PGI2 on components of the adenylate cyclase was examined. The response to forskolin was markedly potentiated by PGI2. PGI2 (3 microM) caused an increase in cAMP of 67 fmol/micrograms over basal in the absence of forskolin, of 164 fmol/micrograms at 10(-7) M forskolin, of 386 fmol/micrograms at 10(-6) M forskolin, and of 563 fmol/micrograms at 10(-5) M forskolin. The response of PGI2 was likewise potentiated by forskolin. Water permeability alone or in response to AVP in isolated perfused inner medullary collecting tubules was not affected by carba-PGI2.(ABSTRACT TRUNCATED AT 250 WORDS)