National recommendations for donation after cardiocirculatory death in Canada: Donation after cardiocirculatory death in Canada

These recommendations are the result of a national, multidisciplinary, year-long process to discuss whether and how to proceed with organ donation after cardiocirculatory death (DCD) in Canada. A national forum was held in February 2005 to discuss and develop recommendations on the principles, procedures and practice related to DCD, including ethical and legal considerations. At the forum's conclusion, a strong majority of participants supported proceeding with DCD programs in Canada. The forum also recognized the need to formulate and emphasize core values to guide the development of programs and protocols based on the medical, ethical and legal framework established at this meeting. Although end-of-life care should routinely include the opportunity to donate organs and tissues, the duty of care toward dying patients and their families remains the dominant priority of health care teams. The complexity and profound implications of death are recognized and should be respected, along with differing personal, ethnocultural and religious perspectives on death and donation. Decisions around withdrawal of life-sustaining therapies, management of the dying process and the determination of death by cardiocirculatory criteria should be separate from and independent of donation and transplant processes. The recommendations in this report are intended to guide individual programs, regional health authorities and jurisdictions in the development of DCD protocols. Programs will develop based on local leadership and advance planning that includes education and engagement of stakeholders, mechanisms to assure safety and quality and public information. We recommend that programs begin with controlled DCD within the intensive care unit where (after a consensual decision to withdraw life-sustaining therapy) death is anticipated, but has not yet occurred, and unhurried consent discussions can be held. Uncontrolled donation (where death has occurred after unanticipated cardiac arrest) should only be considered after a controlled DCD program is well established. Although we recommend that programs commence with kidney donation, regional transplant expertise may guide the inclusion of other organs. The impact of DCD, including pre-and post-mortem interventions, on donor family experiences, organ availability, graft function and recipient survival should be carefully documented and studied.

Use of the embedded peritoneal dialysis catheter: Experience and results from a North American Center

Since 2000, the Ottawa Hospital Home Dialysis Program has used a variation on the embedded peritoneal dialysis catheter technique described by Moncrief et al. In this paper, we describe our approach to placement of peritoneal access and report our experience with 304 embedded catheters placed between January 2000 and December 2003. We review the advantages and disadvantages of this technique and describe factors that have been important to the success of our program.

Proteinuria and reduced kidney function in living kidney donors: A systematic review, meta-analysis, and meta-regression

We reviewed any study where 10 or more healthy adults donated a kidney, and proteinuria, or glomerular filtration rate (GFR) was assessed at least 1 year later. Bibliographic databases were searched until November 2005. 31 primary authors provided additional information. Forty-eight studies from 27 countries followed a total of 5048 donors. An average of 7 years after donation (range 1-25 years), the average 24 h urine protein was 154 mg/day and the average GFR was 86 ml/min. In eight studies which reported GFR in categories, 12% of donors developed a GFR between 30 and 59 ml/min (range 0-28%), and 0.2% a GFR less than 30 ml/min (range 0-2.2%). In controlled studies urinary protein was higher in donors and became more pronounced with time (three studies totaling 59 controls and 129 donors; controls 83 mg/day, donors 147 mg/day, weighted mean difference 66 mg/day, 95% confidence interval (CI) 24-108). An initial decrement in GFR after donation was not accompanied by accelerated losses over that anticipated with normal aging (six studies totaling 189 controls and 239 donors; controls 96 ml/min, donors 84 ml/min, weighted mean difference 10 ml/min, 95% CI 6-15; difference not associated with time after donation (P=0.2)). Kidney donation results in small increases in urinary protein. An initial decrement in GFR is not followed by accelerated losses over a subsequent 15 years. Future studies will provide better estimates, and identify those donors at least risk of long-term morbidity.

Long-term safety and efficacy after conversion of maintenance renal transplant recipients from mycophenolate mofetil (MMF) to enteric-coated mycophenolate sodium (EC-MPA, myfortic)

AIM

A 12-month multicenter, double-blind trial in which maintenance renal transplant patients were randomized to remain on mycophenolate mofetil (MMF) or convert to enteric-coated mycophenolate sodium (EC-MPS, myfortic) has demonstrated that conversion from MMF to EC-MPS is safe. Patients completing the study were invited to enter an open-label extension. Upon entry to the extension, patients who had received MMF during the randomized phase were converted to EC-MPS ("newly-exposed EC-MPS" group) and were monitored separately from those who had been randomized to EC-MPS ("long-term EC-MPS" group). The aim of the extension study was to collect long-term safety and efficacy data on EC-MPS, and to confirm the safety of conversion from MMF to EC-MPS in a larger patient population.

METHODS

All patients received EC-MPS 720 mg b.i.d. with cyclosporine microemulsion and corticosteroids per local practice. Data derived from the analysis of the first 24 months of the extension phase are presented.

RESULTS

Of the 297 patients who completed the core study, 260 (88%) entered the extension; 195 (75%) completed the 24-month extension visit. For on-treatment patients > 95% of the planned daily dose of EC-MPS was administered, and < 13% of patients in both groups had discontinued EC-MPS due to adverse events by 24 months. The overall incidence of adverse events during the extension phase, including infections and hematological abnormalities, was comparable to that seen in the core study, with a similar safety profile in the newly-exposed and long-term EC-MPS groups. There were 3 deaths during the first 24 months of the extension, and 2 graft failures in both the "newly-exposed" and "long-term" EC-MPS groups.

CONCLUSIONS

These data demonstrate that long-term use of EC-MPS is effective and has an acceptable tolerability profile in renal transplant patients, and confirm that conversion of maintenance renal transplant patients from MMF to EC-MPS is a safe therapeutic option.

Meta-analysis: risk for hypertension in living kidney donors

BACKGROUND

The risk for hypertension after kidney donation remains uncertain.

PURPOSE

To see whether normotensive adults who donate a kidney develop higher blood pressure and risk for hypertension compared with nondonor adults acting as control participants.

DATA SOURCES

MEDLINE, EMBASE, and Science Citation Index were searched from 1966 until November 2005 for articles published in any language. Reference lists of pertinent articles were also reviewed.

STUDY SELECTION

The authors selected studies involving 10 or more healthy normotensive adults who donated a kidney and in whom blood pressure was assessed at least 1 year later.

DATA EXTRACTION

Two reviewers independently abstracted data on study and donor characteristics, blood pressure measurements, outcomes, and prognostic features. Comparison data were abstracted from donor studies with control participants. Thirty primary authors provided additional data.

DATA SYNTHESIS

Forty-eight studies from 28 countries followed a total of 5145 donors. Before surgery, the average age of donors was 41 years, the average systolic blood pressure was 121 mm Hg, and the average diastolic blood pressure was 77 mm Hg for all studies. In controlled studies in which the average follow-up was at least 5 years after donation (range, 6 to 13 years), blood pressure was 5 mm Hg higher in donors than in control participants (the weighted mean for systolic blood pressure using 4 studies involving 157 donors and 128 control participants was 6 mm Hg [95% CI, 2 to 11 mm Hg], and the weighted mean for diastolic blood pressure using 5 studies involving 196 donors and 161 control participants was 4 mm Hg [CI, 1 to 7 mm Hg]). There was statistical heterogeneity among the 6 controlled studies that assessed hypertension; an increase in risk was noted in 1 study (relative risk, 1.9 [CI, 1.1 to 3.5]).

LIMITATIONS

Most studies were retrospective and did not include control groups that were assembled and followed along with donors. Approximately one third of the donors had incomplete follow-up information.

CONCLUSIONS

On the basis of the limited studies conducted to date, kidney donors may have a 5-mm Hg increase in blood pressure within 5 to 10 years after donation over that anticipated with normal aging. Future controlled, prospective studies with long periods of follow-up will better delineate safety and identify donors at lowest risk for long-term morbidity.

The impact of accepting living kidney donors with mild hypertension or proteinuria on transplantation rates

BACKGROUND

As waiting times for kidney transplantation increase, individuals with hypertension or proteinuria may be considered as eligible living donors. We set out to determine how frequently donors are excluded because of hypertension or proteinuria and to what extent accepting such donors would increase transplantation rates.

METHODS

Wait lists from 4 Canadian transplantation centers were examined for causes of living kidney donor exclusion. Donors with hypertension (clinic blood pressure >140/90 mm Hg or requiring antihypertensive medication) or proteinuria historically have been excluded at these centers. We define potentially acceptable hypertension as a clinic blood pressure less than 150/100 mm Hg or less than 140/90 mm Hg if administered a single antihypertensive medication and define acceptable proteinuria as protein of 0.15 to 0.3 g/d.

RESULTS

Only 35% (124 of 352 patients) of wait-listed patients had a living donor evaluated (n = 180 potential donors). Primary reasons for donor exclusion were immunologic: a positive cross-match (32%; n = 59) or blood group type incompatibility (22%; n = 40). Hypertension or proteinuria were less common (17%; n = 31). Of 31 donors excluded for hypertension or proteinuria, only 13 had results in the acceptable range. Acceptance of these donors would have resulted in transplantation of 3% (12 of 352 patients) of the wait-list population.

CONCLUSION

Accepting living donors with mild hypertension and proteinuria will lead to a slight increase in transplantation rates. Efforts to improve living donor awareness and overcome immunologic barriers to transplantation may have a greater impact.

Factors associated with publication following presentation at a transplantation meeting

Full publication of abstracts presented at scientific meetings ranges from 25-74%. To determine the rate and factors associated with publication in organ transplantation, we examined abstracts presented at the American Transplant Congress in May 2000. Of 1147 abstracts, 607 (53%) achieved full publication at 4.5 years (mean 1.32 +/- 0.88 years). Fifty-nine percent (357/607) were published in three transplantation journals. For randomized trials, the proportion published was 61%. On multivariate analysis, industry sponsorship (OR 1.78; 95% CI 1.04-3.06), basic science research (OR 1.68; 95% CI 1.32-2.14), non-American center (OR 1.67; 95% CI 1.28-2.20) and oral presentation (OR 1.36; 95% CI 1.07-1.73) were independent predictors of full publication. Nearly half of all abstracts presented at a transplantation meeting remain unpublished. This finding needs to be considered when interpreting systematic reviews in the field of transplantation.

Phosphorus removal and recovery from wastewater by tobermorite-seeded crystallisation of calcium phosphate

Investigations were focused on the development of a technology for phosphorus (P) recovery straight from wastewater. Facing the finiteness of the natural resources of this essential nutrient, the declared goal must be the sustainable use of available phosphorus sinks such as wastewater treatment plants (WWTP) for the generation of P rock substitutes. A feasible method for simultaneous elimination and recovery of phosphorus from wastewater proved to be the P-RoC process - the phosphorus recovery from wastewater by induced crystallisation of calcium phosphate, applying tobermorite-rich waste compounds of the construction industry. The experiments were performed in fixed bed-, stirred- and expanded bed reactors in laboratory--as well as in pilot-scale experiments. The efficiency and longevity of the P-RoC process was determined by the supply of Ca ions and the initial P concentration. Total P (P-tot) contents in the generated crystallisation products of up to 13% P-tot (30% P2O5) were achieved. Mineralogical investigations proved the formation of a hydroxy-apatite-(HAP)-like coating onto the seed material's surface. Reuse options for the generated crystallisation products, such as substitute for phosphate rock or as new fertiliser, were assessed.

Patient survival following renal transplant failure in Canada

Studies from the United States have shown that renal allograft failure is associated with a high mortality rate. The purpose of this study was to determine whether transplant failure was associated with survival in a recent cohort of kidney transplant recipients with different characteristics and a distinct health care system from the United States. Cox regression was used to model allograft loss as a time-dependent variable with patient survival as the primary outcome in 4743 kidney transplant recipients from the Canadian Organ Replacement Register. During follow-up 607 (12.8%) patients had allograft failure and 411 (8.7%) died. Patients with a functioning transplant had an unadjusted death rate of 2.06 per 100 patient years that increased to 5.14 per 100 patient years following allograft failure. After controlling for important confounding variables, allograft failure was found to increase the risk of death by over threefold compared to patients who maintained transplant function (adjusted hazard ratio, 3.39; 95% CI, 2.75-4.16; p < 0.0001). In conclusion, this analysis has shown that kidney transplant failure is an independent predictor of mortality following renal transplantation in a Canadian population. This finding supports the premise that it is the loss of transplant function, rather than patient or system-related issues, that is the main factor contributing to outcome.

Safety and Efficacy After Conversion From Mycophenolate Mofetil to Enteric-Coated Mycophenolate Sodium: Results of a 1-Year Extension Study

Enteric-coated mycophenolate sodium (EC-MPS) is an enteric-coated formulation of mycophenolic acid. A 12-month, multicenter, double-blind, randomized clinical study demonstrated that converting maintenance renal transplant patients from mycophenolate mofetil (MMF) to EC-MPS is safe and does not affect efficacy. In an open-label study extension, 130 patients initially randomized to MMF were converted to EC-MPS (newly exposed); 130 initially randomized to EC-MPS continued on EC-MPS (EC-MPS long-term). A composite endpoint of biopsy-proven acute rejection (BPAR), graft loss, or death occurred in 3 (2.3%) newly exposed and 2 (1.5%) EC-MPS long-term patients during the extension phase. One patient died and one lost his graft. BPAR occurred in 3 (2.3%) newly exposed patients and 1 (0.8%) EC-MPS long-term patient. During the first 12 months of the extension phase, incidence and type of adverse events was similar in both groups and comparable to that seen in the core study. Nine cases of malignancy were reported, mainly nonmelanoma skin cancers. EC-MPS dose adjustments for adverse events were required in <12% of patients. At the end of the 12-month extension, 58 (44.6%) and 64 (49.2%) newly exposed and EC-MPS long-term patients, respectively, had reported at least one gastrointestinal adverse event. Mean serum creatinine remained stable at the 12-month visit of the extension study (137 micromol/L in the newly exposed and 142 micromol/L in the EC-MPS long-term groups). The results of this study demonstrate the long-term safety of EC-MPS and reconfirm the safety of converting MMF maintenance renal transplant patients to EC-MPS.

Peritoneal dialysis patients using sevelamer do not present the acidosis problems that hemodialysis patients do

Acidosis is responsible for catabolic state in dialysis patients and should be avoided or corrected. The survival of patients on peritoneal dialysis (PD) is as good as that of patients on hemodialysis--if not better-mainly because PD patients are rarely in an acidotic-catabolic state as compared with hemodialysis patients. We investigated whether the use of sevelamer in PD patients contributes to significant acidosis as has been reported in the hemodialysis population. We compared serum bicarbonate in 12 PD patients on sevelamer and 77 PD patients not on that drug. Residual renal function, serum phosphate, and daily intake of calcium phosphate binder were also recorded. Patients on PD who take sevelamer maintain a serum bicarbonate level in the normal range as compared with hemodialysis patients, who frequently become acidotic. Serum bicarbonate is only slightly lower in PD patients taking sevelamer than in those not taking that drug.

Challenges in the management of infantile factor H associated hemolytic uremic syndrome

We describe a 1-year old with four episodes of recurrent hemolytic uremic syndrome (HUS). Family history suggested an autosomal dominant mode of inheritance. Factor H concentrations in the blood were normal in the affected family members. Mutation screening in the human complement factor H gene ( HF-1) revealed a novel mutation in exon 23 (c.3546_3581dup36). The HF-1 gene encodes complement factor H and the mutation leads to the insertion of 12 additional amino acids after codon 1176 in factor H. The recurrent HUS responded to plasma infusions and renal function improved from a glomerular filtration rate of 21 to 50 ml/min per 1.73 m(2). The infusions of fresh-frozen plasma were necessary at once-weekly intervals at a dose of 40-45 ml/kg in order to maintain remission and resulted in significant hyperproteinemia. This was addressed by intermittent plasma exchange through an arterio-venous fistula. The prognosis and therapeutic dilemmas are discussed.

The burden of chronic kidney disease in renal transplant recipients

The National Kidney Foundation has developed guidelines for the diagnosis and classification of chronic kidney disease (CKD) but it is not known whether these are applicable to renal transplant recipients. This study determined the prevalence of CKD according to the stages defined in the guidelines, the complications related to CKD and whether the prevalence of complications was related to CKD stage in 459 renal transplant recipients. CKD was present in 412 patients (90%) and 60% were in CKD Stage 3 with a glomerular filtration rate (GFR) between 30 and 59 mL/min/1.73 m2. The prevalence of anemia increased from 0% in Stage 1 to 33% in Stage 5 (p<0.001). Hypertension was present in 86% and increased from 60% in Stage 1 to 100% in Stage 5 (p=0.02). The number of anti-hypertensives per patient increased from 0.7 in Stage 1 to 2.3 in Stage 5 (p<0.001). The number of CKD complications per patient increased from 1.1 in Stage 1 to 2.7 in Stage 5 (p<0.001). We conclude that CKD and the complications of CKD are highly prevalent in renal transplant recipients. The classification of renal transplant patients by CKD stage may help clinicians identify patients at increased risk and target appropriate therapy to improve outcomes.

A partial explanation for the surprising ADEMEX result

Among the many factors contributing to mortality and morbidity in dialysis patients, nutrition is one of the most important. The ADEMEX (Adequacy of Peritoneal Dialysis in Mexico) study suggests that increasing the amount of daily dialysis to compensate for loss of residual renal function (RRF) does not change mortality or morbidity in peritoneal dialysis (PD) patients. Our purpose in the present study was to determine whether a gradual increase in daily dialysis volume to compensate for loss of RRF interferes with the nutrition of patients. We studied the correlation between normalized protein catabolic rate (nPCR) and daily dialysis volume in 150 PD patients. The Student t-test was used to discover if the correlation was statistically significant. We found that, as the daily dialysis volume increases to replace lost RRF, nPCR declines significantly. This reverse relationship was statistically significant at a p value of 0.007. Replacement of lost RRF by an increase in daily dialysis volume in PD patients contributes significantly to their state of protein malnutrition. The large quantity of carbohydrate acquired through dialysis interferes with the patients' intake of protein. The resulting condition of malnutrition probably plays a significant role in mortality and morbidity in those patients.

Ablation of Cypher, a PDZ-LIM domain Z-line protein, causes a severe form of congenital myopathy

Cypher is a member of a recently emerging family of proteins containing a PDZ domain at their NH(2) terminus and one or three LIM domains at their COOH terminus. Cypher knockout mice display a severe form of congenital myopathy and die postnatally from functional failure in multiple striated muscles. Examination of striated muscle from the mutants revealed that Cypher is not required for sarcomerogenesis or Z-line assembly, but rather is required for maintenance of the Z-line during muscle function. In vitro studies demonstrated that individual domains within Cypher localize independently to the Z-line via interactions with alpha-actinin or other Z-line components. These results suggest that Cypher functions as a linker-strut to maintain cytoskeletal structure during contraction.

Spatio-temporal current density reconstruction (stCDR) from EEG/MEG-data

Among the different approaches to the bioelectromagnetic inverse problem, the current-density reconstruction methods (CDR) provide the most general solutions. Since the inverse problem does not have a unique solution, model assumptions have to be taken into account. Multi-channel measurements contain not only spatial, but also temporal information about the sources, so a naturally extension to existing methods leads to spatio-temporal model constraints. Spatio-temporal CDR's (stCDR) have been tested in simplified volume conductor models, assuming different spatial model constraints and a smooth temporal activation model. Comparison to existing spatial model constraints showed a significant improvement of spatial and temporal resolution of the reconstructed sources for the spatio-temporal models especial in noisy data.

Calcium stores in differentiated Dictyostelium discoideum: prespore cells sequester calcium more efficiently than prestalk cells

Dictyostelium discoideum pseudoplasmodia exhibit a gradient of the cytosolic free Ca2+-concentration ([Ca2+]i) along their anterior-posterior axis involved in cell-type specific differentiation. [Ca2+]i is high in prestalk and low in prespore cells. We determined the content and localization of calcium and other elements in cryosectioned cells of pseudoplasmodia and fruiting bodies by X-ray microanalysis. Granular stores rich in Ca, Mg and P were identified. Average Ca was higher in prespore than prestalk granules (225vs 111 mmol/kg dry weight). Total Ca stored in granules was also higher in prespore than prestalk cells. The amount of P and S in granules differed between the two cell types indicating different store composition. In spores mean granular Ca was 120 mmol/kg dry weight. Stalk cells had smaller granules with 360 mmol Ca/kg dry weight. Complementary to microanalysis, vesicular Ca2+-fluxes were studied in fractionated cell homogenates. The rate of Ca2+-uptake was higher in pellet fractions of prespore than prestalk amoebae (4.7 vs 3.4 nmol/min x mg). Ca2+-release was greater in supernatant fractions from prestalk than prespore cells (16.5vs 7.7 nmol/10(8)cells). In summary, prestalk and prespore cells possess qualitatively different, high-capacity stores containing distinct amounts of Ca and probably being involved in regulation of the anterior-posterior [Ca2+]i-gradient.

cAMP-induced changes in the cytosolic free Ca2+ concentration in Dictyostelium discoideum are light sensitive

The cytosolic free calcium concentration ([Ca2+]i) of the social amoeba Dictyostelium discoideum was analyzed after challenge with the chemoattractant cAMP. [Ca2+]i was measured by digital imaging in single cells loaded with the Ca2+ indicator Fura-2-dextran. Global stimulation with low concentrations of cAMP (0.1-1 microM) led to a global transient [Ca2+]i increase. This increase was abolished when cells were illuminated with high doses of light. However, after a short recovery period of several minutes, the cells again displayed the normal response. Inhibition of the [Ca2+]i elevation depended on the wavelength of illumination light. We compared the required recovery period of cells irradiated with either 340, 380, 405, 450 or 490 nm at defined intensities. Light of 405 nm had a pronounced effect; 340 nm alone or in combination with 380 nm was also effective, but to a lesser extent, whereas neither 450 nm nor 490 nm inhibited the [Ca2+]i increase, even at very high irradiance. The wavelength dependence matched the absorption spectrum of amoebae grown in darkness that contain a photopigment which seems to be responsible for phototaxis of single cells. Cells grown in darkness exhibited an increased sensitivity of the cAMP-induced [Ca2+]i transient towards light compared to light-grown cells. From these data we conclude that phototactic signaling could interfere with chemotactic signaling at the level of [Ca2+]i changes.

The influence of skull-conductivity misspecification on inverse source localization in realistically shaped finite element head models

The electric conductivities of different tissues are important parameters of the head model and their precise knowledge appears to be a prerequisite for the localization of electric sources within the brain. To estimate the error in source localization due to errors in assumed conductivity values, parameter variations on skull conductivities are examined. The skull conductivity was varied in a wide range and, in a second part of this paper, the effect of a nonhomogeneous skull conductivity was examined. An error in conductivity of lower than 20% appears to be acceptable for fine finite element head models with average discretization errors down to 3 mm. Nonhomogeneous skull conductivities, e.g., sutures, yield important mislocalizations especially in the vincinty of electrodes and should be modeled.

Inverse localization of electric dipole current sources in finite element models of the human head

The paper describes finite element related procedures for inverse localization of multiple sources in realistically shaped head models. Dipole sources are modeled by placing proper monopole sources on neighboring nodes. Lead field operators are established for dipole sources. Two different strategies for the solution of inverse problems, namely combinatorial optimization techniques and regularization methods are discussed and applied to visually evoked potentials, for which exemplary results are shown. Most of the procedures described are fully automatic and require only proper input preparation. The overall work for the example presented (from EEG recording to visual inspection of the results) can be performed in roughly a week, most of which is waiting time for the computation of the lead field matrix or inverse calculations on a standard and affordable engineering workstation.

Calcium-sequestering organelles of Dictyostelium discoideum: changes in element content during early development as measured by electron probe X-ray microanalysis

Starving Dictyostelium discoideum amoebae aggregate within a few hours by chemotaxis towards the attractant cAMP to form a multicellular organism. The differentiating cells possess rapid and efficient calcium buffering and sequestration systems which enable them to restrict changes in the cytosolic free calcium concentration temporally and spatially during their chemotactic reaction and allow the continuous accumulation of Ca2+ during development. In order to identify and to characterize calcium storage compartments, we analyzed the element content of amoebae at three consecutive stages of differentiation. Determination of the element distribution was done using energy-dispersive X-ray microanalysis of freeze-dried cryosections of rapid-frozen cells. Amoebae were frozen in the vegetative and aggregation-competent state and after formation of aggregates. Aggregation-competent as well as aggregated cells contained mass dense granules with large amounts of calcium together with phosphorous and either potassium or magnesium: in aggregation-competent cells calcium was colocalized with potassium, whereas in aggregated cells the mass dense granules contained calcium and magnesium. Although mass dense granules were also present in undifferentiated, vegetative cells, they contained only low amounts of phosphorous and potassium together with little Ca and Mg. We conclude that during their differentiation D. discoideum cells use an intracellular storage compartment to sequester Ca and other cations constantly throughout development.

Challenge with high concentrations of cyclic AMP induces transient changes in the cytosolic free calcium concentration in Dictyostelium discoideum

Dictyostelium discoideum cells use cyclic AMP (cAMP) for chemotactic signaling as well as for differentiation. The precise regulation of the cytosolic Ca2+ concentration ([Ca2+]i) seems to play a key role for both processes. We performed single cell measurements of [Ca2+]i in amoebae that were starved in suspension for various times and scrape-loaded with the Ca2+ indicator fura-2. Stimulation of cells with cAMP at the concentration required to induce gene expression (&gt; or = 100 microM) elicited a global transient increase in [Ca2+]i that depended on the presence of external Ca2+. Both vegetative and aggregation-competent cells displayed a rise in [Ca2+]i, with aggregation-competent cells responding more often than vegetative cells. Basal [Ca2+]i in the presence of Ca2+ was high in vegetative cells and declined during development; the cAMP-induced rise in [Ca2+]i was higher and lasted longer in vegetative cells than in aggregative cells. The addition of 2′-deoxy-cAMP, which binds to the cAMP receptor, induced an increase in [Ca2+]i, whereas the membrane-permeant analogue 8-bromo-cAMP that has a low affinity for the receptor but activates cAMP-dependent protein kinase had no effect. This indicates that the change in [Ca2+]i is mediated by the cell surface cAMP receptor. Since HC85 mutant cells, which lack the G alpha 2 subunit of the G-protein that couples the receptor to phospholipase C, also responded to stimulation with cAMP, the Ca2+ influx does not seem to be triggered by the phosphoinositide signaling cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

A calcium influx is neither strictly associated with nor necessary for exocytotic membrane fusion in Paramecium cells

Exocytosis of trichocysts in Paramecium cells was generally believed to depend on extracellular Ca, since it is accompanied by a Ca influx and not seen in the absence of Ca. However, by short term removal of Ca we showed recently that only extrusion of secretory contents, but not membrane fusion after stimulation with aminoethyldextran (AED), depends on extracellular Ca. We have now extended these studies to longer times and shown that membrane fusion is stimulated by AED even after 1 min at low Ca (< or = 30 nM). At prolonged times membrane fusion was induced by sole removal of Ca. In the presence of AED, trichocyst contents were slowly extruded followed by resealing of the fused membranes, indicating independency of endocytotic membrane fusion from extracellular Ca (though we observed aberrant resealing). Later on, Ca removal is followed by cell death. By using videomicroscopy, we further provide the first evidence that exocytosis is not necessarily accompanied by an influx of Ca in the presence of the usual high concentrations (1 mM), since local exocytosis at the rear end of the cells is not followed by ciliary reversal which is triggered by Ca influx. We conclude that a Ca influx is neither regularly associated with, nor necessary for, induction of exocytotic membrane fusion in Paramecium cells. As a source for a possible alternative intracellular liberation of calcium during exocytosis, we analyzed the subplasmalemmal alveolar sac system by electron spectroscopic imaging and found indications for Ca redistributions shortly after stimulation.

Antiglomerular basement membrane antibody-mediated nephritis with normal pulmonary and renal function. A case report and review of the literature

Antiglomerular basement membrane (anti-GBM) antibody-mediated disease is usually characterized by a rapidly progressive glomerulonephritis with or without pulmonary hemorrhage. We report a case of anti-GBM-mediated nephritis that presented with hematuria and proteinuria. There was no evidence of renal insufficiency or pulmonary hemorrhage. Clinicians should be aware of this rare presentation of anti-GBM-mediated nephritis.

Exo-endocytosis in isolated peptidergic nerve terminals occurs in the sub-second range

Exo- and endocytotic processes induced by depolarization of isolated neurosecretory nerve terminals show a close temporal correlation, which suggests a short time of integration of the neurosecretory granule membrane with the plasma membrane. In order to determine minimal time requirements for exocytosis-coupled endocytosis to occur, we have analyzed by electron microscopy uptake of horseradish peroxidase (HRP) as a fluid phase marker at the onset of depolarization. We have applied rapid mixing and sampling (quenched flow) to assess events in sub-second time periods after stimulation. A significant number of labelled endocytotic vacuoles was observed during the first second of depolarization. This number then further increased by a factor of about 2 (within 5 s) and 4 (within 50 s). Thus, as for exocytosis, the rate of endocytosis decreased considerably during prolonged stimulation. These data indicate i) that a substantial proportion of secretory granules undergoes exocytosis very shortly after stimulation, and ii) that, following exocytosis, the minimal time required for consecutive membrane retrieval is in the sub-second range.

A cortical phosphoprotein ('PP63') sensitive to exocytosis triggering in Paramecium cells. Immunolocalization and quenched-flow correlation of time course of dephosphorylation with membrane fusion

We had previously shown that a phosphoprotein of 63 kDa ('PP63') is rapidly and selectively dephosphorylated during synchronous (less than or equal to 1 s) trichocyst exocytosis in Paramecium cells and then rephosphorylated within less than or equal to 1 min [Zieseniss & Plattner (1985) J. Cell Biol. 101, 2028-2035]. Using a new quenched-flow device, we now find a strict correlation between PP63 dephosphorylation and the process of membrane fusion, both occurring within 80 ms. Uptake of 32P over 90 min, followed by exocytosis and rephosphorylation for 1 min, results in a rather selective phosphorylation of the dephosphorylated form, P63, to PP63. Solubilization by repeated freezing and thawing allows isolations of P63 and PP63. On isoelectric focusing autoradiograms they have pI values of 6.05, 5.95 (major spots), 5.85 and 5.75. All spots are sensitive to alkaline, but not to acidic, hydrolysis (except for the pI-6.05 spot). On two-dimensional-gel autoradiograms the most prominent spot, of pI 5.95, is most extensively de- and re-phosphorylated. This spot, from de- and re-phosphorylated samples, was used to produce monospecific antibodies. A cortical localization of PP63 was revealed by producing Western blots from isolated cell-surface fragments ('cortices') and by immunofluorescence labelling. We assume that both P63 and PP63 are attached to cortical structures, e.g. around trichocysts, though they are partly soluble. This localization and the strict correlation of PP63 dephosphorylation with exocytotic membrane fusion suggests a role in fusion regulation.

A rapid calcium influx during exocytosis in Paramecium cells is followed by a rise in cyclic GMP within 1 s

The synchrony of trichocyst exocytosis in Paramecium allows temporal correlation of associated events. Using quenched flow we observed a Ca2+ influx concurrent with exocytosis within 80 ms after stimulation with the secretagogue aminoethyldextran. Cyclic AMP did not change in depency of stimulation. Cyclic GMP transiently increased after 500 ms, culminating at 2 s, and thus considerably lags behind exocytosis induction and influx of Ca2+. Both Ca2+ influx and rise in cGMP are known to be induceable also by Ba2+ or veratridine, allegedly via the opening of ciliary Ca2+ channels. However, only veratridine stimulated exocytosis. We conclude that both aminoethyldextran and veratridine induce an exocytosis-associated Ca2+ influx, which is responsible for the rise in cGMP, through an as yet unknown pathway.

Quantitative immuno-gold labelling and ultrastructural preservation after cryofixation (combined with different freeze-substitution and embedding protocols) and after chemical fixation and cryosectioning. Analysis of the secretory organelle matrix of Paramecium trichocysts

Among the variety of parameters affecting immuno-gold labelling efficiency, mainly the effects of different preparative protocols were tested. Preservation of ultrastructure and of antigenicity are the salient features of this study. We have labelled insoluble components of the secretory matrix of Paramecium trichocysts with specific antisera, using 10 nm colloidal gold particles. The highest labelling efficiency was obtained with fast freezing (cryofixation, either by sandwich or spray-freezing), freeze-substitution in methanol (without added fixatives) and hydrophilic Lowicryls, particularly when applied at low temperatures (K11M at 193 K). The presence of different chemical fixatives always reduced the labelling density and some recommendations from the literature do not appear advisable. Methods commencing with fixation at greater than or equal to 0 degree C, such as "progressive lowering of temperature" (PLT) or preparation of cryostat sections, i.e. with chemical pretreatments, always resulted in lower labelling density. Our data appear, therefore, relevant for optimal immuno-gold labelling of insoluble antigens and emphasize the potential of cryofixation as a primary preparation step. In addition, ultrastructural preservation was also superior after cryofixation.

Intracellular calcium during chemotaxis of Dictyostelium discoideum: a new fura-2 derivative avoids sequestration of the indicator and allows long-term calcium measurements

During stimulation of Dictyostelium discoideum amoebae with the chemoattractant cAMP, extracellular calcium is taken up by the cells. The aim of this study was to determine the cytosolic free calcium concentration ([Ca++]i) during chemotaxis of Dictyostelium cells. In contrast to most vertebrate cells, three major drawbacks were encountered: 1) the indicator fura-2 could not be introduced into the cells by incubation with the ester form, 2) once loaded, the dye was rapidly sequestered into vesicles, 3) the organic anion transport blocker probenecid was not suitable to block sequestration. These problems were met by introducing the indicator into the cells with the scrape-loading technique adapted for use with Dictyostelium and the construction of a new fura-2 derivative, fura-2-dextran. Scrape-loading of Dictyostelium yielded up to 40% of labeled, vital cells. Fura-2-dextran fulfilled the following criteria: 1) it remained homogeneously distributed in the cytoplasm of motile Dictyostelium cells, 2) it retained the fluorescence intensity of fura-2 and the affinity for calcium binding, 3) it was very well suitable to demonstrate changes of [Ca++]i in serum-stimulated fibroblasts. [Ca++]i-measurements with fura-2-dextran in chemotactically active D. discoideum amoebae revealed that the large decrease in the extracellular calcium concentration is not accompanied by an overall change in [Ca++]i. Chemotaxis in this organism occurs in the absence of global changes in [Ca++]i. However, we cannot exclude either short-lived or local changes just beneath the plasma membrane.

A preparation method of specimens of the fungus Penicillium chrysogenum for ultrastructural and immuno-electron microscopical studies

A combination of cryofixation without pre-treatment, freeze-substitution and low-temperature embedding was used to prepare specimens of Penicillium chrysogenum for electron microscopy. To produce specimens which are thin enough for appropriate cryofixation, the P.chrysogenum colonies were grown between dissected-dialysis tubing on an agar plate, which in addition allowed longitudinal sectioning. In contrast to classical chemical fixation, this preparation procedure resulted in excellent preservation of ultrastructure. Furthermore, the penicillin biosynthetic enzyme acyltransferase could be unequivocally located by immunogold labelling, indicating a preservation of antigenic properties of the specimen. Labelling density was not conspicuously affected when using different freeze-substitution media, but it was reduced after embedding in Epon 812.

Effect of intracoronary diltiazem on infarct size and regional myocardial function in the ischemic reperfused canine heart

This study was designed to investigate whether intracoronary diltiazem given before reperfusion could enhance myocardial salvage in the canine heart. Twenty-five dogs were subjected to 90 min of coronary occlusion followed by 4 h of reperfusion. The dogs were assigned to one of three experimental groups. The early diltiazem group received intracoronary diltiazem into the distal coronary bed at the onset of coronary occlusion and for 60 min after reperfusion. The late diltiazem group received the same amount of drug beginning 15 min before reperfusion and the control group received saline solution for 90 min of occlusion and 60 min of reperfusion. Infarct size expressed as a percent of the area at risk was significantly smaller in the early and late diltiazem groups (15.6 +/- 3.6% and 21.2 +/- 5.1%, respectively) than in the control group (49 +/- 4.6%) (p less than 0.05). Intracoronary diltiazem restored systolic function of the stunned, previously ischemic tissue to essentially normal preocclusion values. Segmental shortening after reperfusion averaged 21.6% in the early diltiazem group versus 0 +/- 1.7% and 7.3 +/- 4% for the control and late diltiazem groups, respectively (p less than 0.05). Low dose intracoronary diltiazem did not alter hemodynamic variables or myocardial blood flow but did improve segmental shortening 2 and 6 h after reperfusion. These data indicate that intracoronary diltiazem given during occlusion or just before reperfusion increases the salvage of myocardium compared with the salvage achieved by reperfusion alone. These results also suggest that intracoronary diltiazem given during the ischemic period enhances systolic contractile function of postischemic stunned myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Quenched flow analysis of exocytosis in Paramecium cells: time course, changes in membrane structure, and calcium requirements revealed after rapid mixing and rapid freezing of intact cells

Synchronous exocytosis in Paramecium cells was analyzed on a subsecond time scale. For this purpose we developed a quenched flow device for rapid mixing and rapid freezing of cells without impairment (time resolution in the millisecond range, dead time approximately 30 ms). Cells frozen at defined times after stimulation with the noncytotoxic secretagogue aminoethyldextran were processed by freeze substitution for electron microscopic analysis. With ultrathin sections the time required for complete extrusion of secretory contents was determined to be less than 80 ms. Using freeze-fracture replicas the time required for resealing of the fused membranes was found to be less than 350 ms. During membrane fusion (visible 30 ms after stimulation) specific intramembranous particles in the cell membrane at the attachment sites of secretory organelles ("fusion rosette") disappear, possibly by dissociation of formerly oligomeric proteins. This hitherto unknown type of rapid change in membrane architecture may reflect molecular changes in protein-protein or protein-lipid interactions, presumably crucial for membrane fusion. By a modification of the quenched flow procedure extracellular [Ca++] during stimulation was adjusted to less than or equal to 3 x 10(-8) M, i.e., below intracellular [Ca++]. Only extrusion of the secretory contents, but not membrane fusion, was inhibited. Thus it was possible to separate both secretory events (membrane fusion from contents extrusion) and to discriminate their Ca++ requirements. We conclude that no Ca++ influx is necessary for induction of membrane fusion.

Reconstitution of Na+/K+-ATPase into phosphatidylcholine vesicles by dialysis of nonionic alkyl maltoside detergents

The reconstitution of Na+/K+-ATPase from outer medulla of rabbit kidney into large unilamellar liposomes was achieved through detergent removal by dialysis of mixed micellar solutions of synthetic dioleoyl phosphatidylcholine/octyl glucoside and Na+/K+-ATPase/decyl maltoside or decenyl maltoside. Tight, transport-active liposomes were formed when the lipid and the enzyme were solubilized separately in the nonionic detergents and mixed immediately before starting the dialysis. The two maltoside detergents with different structures of the hydrophobic part of the molecule proved to be well suited for the solubilization of Na+/K+-ATPase with high retention of enzyme activity; the inactivation of enzyme being evidently slower with the unsaturated decenyl maltoside. The diameters of the proteoliposomes, 110 and 170 nm, respectively, were also dependent on the structure of the maltoside detergent, the saturated decyl maltoside producing the bigger liposomes. After freeze-fracture, both preparations exhibited intramembranous particles as structural indicators of successful reconstitution. The electrogenic activity of the reconstituted enzyme was determined by fluorescence measurements with Oxonol VI and by tracer-flux measurements with 22Na+.

Fusion of liposomes with the plasma membrane of epithelial cells: fate of incorporated lipids as followed by freeze fracture and autoradiography of plastic sections

The fusion of liposomes with the plasma membrane of influenza virus-infected monolayers of an epithelial cell line, Madin-Darby canine kidney cells (van Meer et al., 1985. Biochemistry. 24:3593-3602), has been analyzed by morphological techniques. The distribution of liposomal lipids over the apical and basolateral plasma membrane domains after fusion was assessed by autoradiography of liposomal [3H]dipalmitoylphosphatidylcholine after rapid freezing or chemical fixation and further processing by freeze substitution and low temperature embedding. Before fusion, radioactivity was solely detected on the apical cell surface, indicating the absence of redistribution artifacts and demonstrating the reliability of lipid autoradiography on both a light and electron microscopical level. After induction of fusion by a low pH treatment, the basolateral plasma membrane domain became progressively labeled, indicative of rapid lateral diffusion of [3H]dipalmitoylphosphatidylcholine in the plasma membrane. Analysis of individual fusion events by freeze fracture after rapid freezing confirmed the rapid diffusion of the liposomal lipids into the plasma membrane, as intramembrane particle-free lipid patches were never observed. After the induction of liposome-cell fusion, well-defined intramembrane particles were present on the otherwise smooth liposomal fracture faces and on the fracture faces of the plasma membrane. Morphological evidence thus was obtained in favor of a local point fusion mechanism with an intramembrane particle as a specific structural fusion intermediate.

Influenza virus-model membrane interaction. A morphological approach using modern cryotechniques

The membrane fusion activity of influenza virus was characterized morphologically using a model system composed of a highly purified influenza B virus suspension and ganglioside-containing zwitterionic liposomes. Electron microscopical analysis was performed after a combination of fast-freezing with either freeze-fracture or freeze-substitution-thin sectioning, ensuring maximal time resolution and avoiding preparation artifacts. In a parallel fluorescence 'lipid mixing' fusion assay, influenza virus-membrane fusion was characterized biochemically. Biochemical and morphological data are in full agreement, indicating negligible membrane fusion activity at neutral pH and high fusion activity at low pH. The freeze-fracture morphology strongly suggests a local point contact between viral and liposomal membrane at neutral pH, and a local point fusion mechanism for influenza virus-membrane fusion upon lowering of the pH. Fusion is followed by lipid mixing, lateral diffusion of viral spike proteins and exposure of viral contents at the inner liposomal surface.

Ultrastructural analysis of dynamic cellular processes: a survey of current problems, pitfalls and perspectives

Dynamic phenomena in cells that can be analyzed on the ultrastructural level comprise so different aspects as ion shifts, conformational changes of macromolecules, membrane particle rearrangements, lipid phase transitions, protein-protein interactions (notably ligand-receptor interactions, including their sorting and sequestration), reversible membrane-to-membrane contacts, membrane fusions, transcellular transport phenomena, restructuring of cytoskeletal elements, ciliary and flagellar beat, cell shape changes, etc. Only some of these phenomena can be analyzed under stationary conditions, while others are unidirectional and sometimes very rapid. Therefore, the methodical approaches to be used (primary methods and follow-up procedures) might be widely different. Quite different methods are available, such as fast freezing, specific labeling, low temperature processing and/or analysis, x-ray-microanalysis, etc. Only occasionally are there alternative non-ultrastructural control methods available. This survey paper tries to analyze the degree of reliability (or uncertainty) of current methods and to pinpoint the goals and eventually also new methodical perspectives for an integrative approach to analyze dynamic cellular processes with the high temporal and spatial resolution provided by the electron microscope.

The regulation of mitochondrial-bound hexokinases in the liver

A functional coupling between bound hexokinase and the inner mitochondrial compartment has been shown. It is based structurally on the binding of hexokinase to a pore protein which is present in zones of contact between the two boundary membranes. The latter was observed by electron microscopic localization of antiporin and hexokinase at the mitochondrial surface. The four isoenzymes present in liver differ considerably in their activity after binding to the mitochondrial surface. This was found by binding studies using the four isoenzymes isolated from the supernatant. Isoenzyme IV did not bind at all. Isoenzymes I-III did bind and became activated: I, 5.9-fold; II, 39-fold; and III, 1.3-fold. These results suggest that the in vivo activity of hexokinase in the mitochondrial fraction is much larger than so far observed. Furthermore the binding of isoenzymes was differently affected by metabolites. Glucose-6-phosphate exclusively desorbed isoenzyme I from the mitochondrial membrane whereas free fatty acids predominantly liberated isoenzymes II and III. A reciprocal change of the levels of free fatty acids and glucose 6-phosphate in livers of starved rats therefore, can explain why exclusively mitochondrial-bound isoenzymes II and III decreased 10-fold while at the same time isoenzyme I increased.

Alterations in liver mitochondrial function as a result of fasting and exhaustive exercise

The effect of exercise upon liver mitochondria structure and function was examined in fasted and fed rats, following a single run to exhaustion on a motor-driven treadmill. Exercise alone and exercise coupled with fasting both produced a significant decrease in the amount of hexokinase bound to the mitochondria, as well as reduction in the ADP/O ratio and acceptor control index measured in the presence of succinate. The mitochondria of the exercised animals, when exposed to freeze-fracture analysis while in state 3, displayed fewer deflections in the fracture plane between the inner and outer membrane than those isolated from control animals. This suggests that fewer contacts existed between the two membranes. Measurements based upon the binding of 8-anilinonaphthalene 1-sulphonate indicated that there was an increase in the net negative charge on the surface of the mitochondrial membranes of the exercised animals. All of these effects could be mimicked by incubation of mitochondria from control animals with free fatty acids. This fact, coupled with the observation that washing of the mitochondria with a solution comprising 5% (w/v) albumin could reverse all of the consequences of exercise, suggests that these alterations in mitochondrial structure and function may be the result of the increase in plasma free fatty acids that accompanies long-term exercise. Furthermore, the observation that the exercise-induced changes are dynamic and readily reversible indicates that the mitochondria were not necessarily damaged, but rather that the coupling of oxidative phosphorylation may be subject to physiological regulation.

Changes in freeze-fractured mitochondrial membranes correlated to their energetic state. Dynamic interactions of the boundary membranes

Structural changes of mitochondria in correlation to their energetic state have been observed as matrix expansion and condensation. In this communication we describe a morphological correlation in freeze-fractured mitochondrial membranes which is also dependent on the metabolic state of the organelle: the frequency by which the fracture plane following the inner or outer boundary membrane deviates by jumping from one membrane to the other is higher in phosphorylating mitochondria when compared to freshly isolated or energized mitochondria. These deflections of the fracture plane occur mostly in minimal, short steps showing close apposition of the two boundary membranes. We therefore conclude that the observed change in morphological appearance is produced by a change in interactions between the inner and outer membranes correlated to the different functional states of the inner membrane.