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Biomedical subjects

J Hoyer

Publications and source records attributed to J Hoyer.

At least 37 records · Page 2Linked to original sources
PubMed2000

Expression and function of endothelial Ca(2+)-activated K(+) channels in human mesenteric artery: A single-cell reverse transcriptase-polymerase chain reaction and electrophysiological study in situ.

Ca(2+)-activated K(+) (K(Ca)) channels have been suggested to play a role in the control of endothelial functions such as regulation of vascular tone and cell proliferation. We established a method for single-cell reverse transcriptase-polymerase chain reaction analysis in combination with the patch-clamp technique to characterize K(Ca) channel expression and function in single endothelial cells (ECs) within the endothelial monolayer of intact human mesenteric arteries (MAs) and in disease states. We tested whether endothelial K(Ca) channel expression and function are altered in MAs obtained from patients with colonic adenocarcinoma (CA) compared with those in MAs from non-cancer patients with inactive diverticulitis. Expression of the intermediate-conductance K(Ca) channel (hIK1) was detected in non-cancer and CA patients. In whole-cell patch-clamp measurements, only ECs expressing hIK1 exhibited corresponding K(Ca) currents, whereas respective K(Ca) currents were missing in hIK1-negative ECs. This heterogeneity of hIK1 expression patterns is indicative of a specialized subset of ECs within the endothelial monolayer. In CA patients, compared with non-cancer patients, a 2.5-fold increase in hIK1-expressing ECs per MA was observed (P:<0.05). However, K(Ca) current densities in hIK1-expressing ECs of both groups were similar. In addition to hIK1, expression of the large-conductance K(Ca) channel (hSlo) was detected in single ECs from CA patients. The increased K(Ca) channel expression in CA patients resulted in a 2. 7-fold increase of bradykinin-induced endothelial hyperpolarization compared with controls (P:<0.05). This increased expression and function of K(Ca) channels might indicate an altered functional state of the endothelium in cancer patients and could play a role in tumor angiogenesis.

Adenocarcinoma↗
PubMed2000

Monitoring of anti-HLA class I and II antibodies by flow cytometry in patients after first cadaveric kidney transplantation.

While the relevance of pre-formed anti-human leukocyte antigen (HLA) antibodies has been studied extensively, the role of anti-HLA class I and II antibodies produced after cadaveric kidney transplantation is still a matter of discussion. As it has been proposed that they are involved in a considerable number of cases, it should be investigated whether a post-transplant monitoring is a sensitive parameter for the early diagnosis of acute rejection episodes. Additionally, it has been suggested that antibodies are a major cause for chronic rejection; thus, it would be of interest to correlate antibody detection and graft survival. We retrospectively investigated 59 patients after a first cadaveric kidney transplantation without known anti-HLA antibodies (complement-dependent cytotoxicity [CDC] testing). The panel reactivity was determined with a new highly sensitive and specific flow-cytometric technique (Flow-PRA Screening Test, One Lambda, Canoga Park, USA) in sequentially collected serum samples pre- and post-transplant. In patients with acute rejection episodes during the clinical course, the last sample prior to rejection, and in patients without rejection, the last sample prior to discharge, was analyzed. Furthermore, we analyzed 3-yr graft survival and several clinical parameters such as cold ischemia time (CIT). Twenty-four of 59 patients (41%) experienced acute rejections during the clinical course. Five of 59 died with a functioning graft within the first 3 yr. Seven of 54 patients, still alive after 3 yr, lost their graft. Anti-HLA antibodies were detectable in only 7/59 patients and a correlation between antibody positivity and acute rejections (p = 0.32 and 0.54 for anti-HLA class I and II, respectively) could not be identified (sensitivity 12.5 and 8.3%). However, we found a significant correlation between the detection of anti-HLA class II and graft loss within 3 yr (p = 0.005, specificity 97.9%). Additionally, anti-HLA class II positive patients had significantly longer CIT (p = 0.003). Whether the detection of anti-HLA class II antibodies in the early post-transplant phase is of great value for the identification of patients at high risk for early graft loss needs additional investigation. However, we found that anti-HLA antibodies are detectable only in a minority of unsensitized patients and we conclude that flow-cytometric monitoring with Flow PRA is not a sensitive parameter for the early diagnosis of acute rejection episodes in patients after first cadaveric kidney transplantation.

Acute Disease↗
PubMed2000

Self-reflection and well-being: is there a healthy amount of introspection?

Both extremely high and extremely low self-reflection have been considered as risk factors for psychological maladjustment. Therefore, from an integrating perspective medium amounts of self-reflection may constitute "healthy introspection." To test this hypothesis, self-reflection and psychological well-being were measured with self-report tests given a pooled sample of 647 subjects. A regressive relationship with self-reflection as a quadratic predictor of well-being was estimated using the LMS method for nonlinear structural equation modeling. No evidence for a curvilinear effect was detected in the total sample or in subgroups. Alternative theoretical assumptions are discussed on a psychological and operational level.

Adolescent↗
PubMed2000

Endothelial K(+) channel lacks the Ca(2+) sensitivity-regulating beta subunit.

Hyperpolarizing large-conductance, Ca(2+)-activated K(+) channels (BK) are important modulators of vascular smooth muscle and endothelial cell function. In vascular smooth muscle cells, BK are composed of pore-forming alpha subunits and modulatory beta subunits. However, expression, composition, and function of BK subunits in endothelium have not been studied so far. In patch-clamp experiments we identified BK (283 pS) in intact endothelium of porcine aortic tissue slices. The BK opener DHS-I (0.05-0.3 micromol/l), stimulating BK activity only in the presence of beta subunits, had no effect on BK in endothelium whereas the alpha subunit selective BK opener NS1619 (20 micromol/l) markedly increased channel activity. Correspondingly, mRNA expression of the beta subunit was undetectable in endothelium, whereas alpha subunit expression was demonstrated. To investigate the functional role of beta subunits, we transfected the beta subunit into a human endothelial cell line (EA.hy 926). beta subunit expression resulted in an increased Ca(2+) sensitivity of BK activity: the potential of half-maximal activation (V(1/2)) shifted from 73.4 mV to 49.6 mV at 1 micromol/l [Ca(2+)](i) and an decrease of the EC(50) value for [Ca(2+)](i) by 1 microM at +60 mV was observed. This study demonstrates that BK channels in endothelium are composed of alpha subunits without association to beta subunits. The lack of the beta subunit indicates a substantially different channel regulation in endothelial cells compared to vascular smooth muscle cells.

Animals↗
PubMed1999

The IL-4 receptor alpha-chain variant Q576R is strongly associated with decreased kidney allograft survival.

The involvement of the interleukin-4 (IL-4) pathway in B-lymphocyte activation and induction of a T helper 2 (Th2) cell response prompted us to investigate the influence of a recently described gain-of function mutation in the IL-4 receptor alpha-chain gene (IL-4R alpha; CD 124) on renal allograft survival. We developed a genotyping assay for the IL-4R alpha variant Q576R and investigated 203 renal transplant patients, all of whom underwent transplantation surgery at a single institution. The overall frequency of the IL-4R alpha variant Q576R in this group was 38.9% (79/203). The Kaplan-Meier method was used to estimate the graft survival of 156 patients with complete follow-up time of 24 months. Significantly higher graft survival rates (P=0.012, log-rank test) were found in patients with the wild-type IL-4 receptor (2-year graft survival 78.8%) as compared to patients with the IL-4R alpha variant Q576R (2-year graft survival 60.6%). Multifactorial cox regression analysis showed that this effect was independent of HLA matching, sex of donor and recipient, age of recipient, year of transplantation and preformed antibodies (P=0.017). These results indicate a strong association of the IL-4R alpha variant Q576R with kidney allograft loss. Genotyping of kidney allograft recipients for the IL-4R alpha variant may offer a simple method to identify high-risk patients in the post-transplantation period.

B-Lymphocytes↗
PubMed1999

Increased mechanosensitive currents in aortic endothelial cells from genetically hypertensive rats.

OBJECTIVE: To characterize and compare mechanosensitive cell currents in rat aortic endothelial cells from spontaneously hypertensive and Wistar-Kyoto rats. METHODS AND RESULTS: By use of the patch-clamp technique, we investigated whole-cell currents of native rat aortic endothelial cells in the presence of mechanical stimulation elicited by hyposmotic cell swelling. In rat aortic endothelial cells, this hypotonic cell swelling induced a fourfold increase in outward-directed whole-cell currents carried by K+, leading to cell hyperpolarization and a small increase in inward-directed currents. Gadolinium, a blocker of stretch-activated cation channels, completely blocked hypotonic cell swelling-induced outward- and inward-directed whole-cell currents. Charybdotoxin, a blocker of Ca(2+)-dependent K+ channels, decreased hypotonic cell swelling-induced outward-directed currents by up to 85%. Disruption of actin filaments by cytochalasin B and of microtubuli by nocodazole reduced the activation of hypotonic cell swelling-induced whole-cell currents by 91 and 71%, respectively. In experimental hypertension, hypotonic cell swelling-induced whole-cell conductance was significantly increased in spontaneously hypertensive rats (331 +/- 20 pS/pF) compared with normotensive controls (167 +/- 7 pS/pF, P < 0.01), whereas basal and agonist-induced cell conductances were not altered. CONCLUSIONS: Increased hypotonic swelling-induced currents in aortic endothelial cells from spontaneously hypertensive rats presumably reflect an increased density or mechanosensitivity of stretch-activated ion channels in experimental hypertension. The increased mechanosensitive whole-cell currents might indicate an altered endothelial mechanotransduction in experimental hypertension.

Adenosine Triphosphate↗
PubMed1998

Pressure-activated cation channel in intact rat endocardial endothelium.

OBJECTIVE: The endocardial endothelium (EE) regulates myocardial performance in response to humoral and mechanical stimuli. In vascular endothelium mechanosensitive ion channels (MSC) act as mechanosensors for hemodynamic changes. In the present study we examined whether MSC are present in intact EE of rat papillary muscle segments and characteristics of MSC are altered in experimental hypertension. METHODS: MSC were investigated by the use of standard patch-clamp technique. For a comparative study, ion channel characteristics were determined in EE of two-kidney-one-clip rats and sham-operated controls. RESULTS: We identified a new class of MSC with a mean conductance of 21.8 +/- 4.4 (s.d.) pS for K+ and Na+ and of 4.1 +/- 1.5 pS for Ca2+. Channel activity was initiated by positive pipette pressure and blocked by negative pipette pressure. Channel open probability (Po) was characterized by its pressure sensitivity. Po increased from 0.06 at 10 mmHg to 0.37 and 0.55 at 20 mmHg and 30 mmHg, respectively. Gadolinium (20 microM), a blocker of MSC, completely inhibited channel activity. In some experiments activation of this pressure-activated channel (PAC) was followed by the opening of a Ca2(+)-dependent non-selective cation channel (NSC). This indicates that Ca2+ influx through PAC may be sufficient to increase intracellular Ca2+ concentration and thereby to activate neighboring NSC. In renovascular hypertension (2K1C), channel density of PAC was significantly increased compared to sham-operated controls. Channel density of NSC was not changed in 2K1C compared to sham-operated controls. CONCLUSION: A novel type of Ca2+ permeable MSC in intact EE of rat ventricular papillary muscle was identified, which is regulated by membrane pressure. PAC might be implicated in EE mechanotransduction by inducing an intracellular Ca2+ signal. Up-regulation of PAC density in EE from 2K1C might contribute to an altered mechanotransduction in hypertension.

Animals↗
PubMed1998

Mechanosensitive Ca2+ oscillations and STOC activation in endothelial cells.

Activation of ion channels and the increase in intracellular Ca2+ concentration [Ca2+]i play a key role in endothelial responses to hemodynamic forces and subsequent vasoregulation. In bovine aortic endothelial cells subjected to shear stress in a parallel flow chamber, we demonstrate shear stress activation of hyperpolarizing K+ currents that occur simultaneously with oscillating increases of [Ca2+]i. Oscillating K+ currents, also known as spontaneous transient outward currents (STOC), were regulated in frequency and amplitude by the rate of shear stress in a range from 5 to 18 dyn/cm2. Activation of STOC depended on Ca2+ influx; current depended on the extracellular Ca2+ concentration and was blocked by 50 microM Gd3+. Emptying of Ca2+ stores by BHQ abolished current responses to shear stress. STOC activation was significantly reduced by cell dialysis with ryanodine (20 microM), but not heparin (200 microg/ml). Shear stress-induced STOC activation was also observed in the intact endothelium. The endothelial response to shear stress involves oscillating [Ca2+]i increase and STOC activation, which depend on Ca2+ influx-induced Ca2+ release from ryanodine-sensitive stores, demonstrating a new signaling pathway in endothelial mechanotransduction.

Animals↗
PubMed1998

Stretch-activated cation channel in human umbilical vein endothelium in normal pregnancy and in preeclampsia.

OBJECTIVE: To determine whether stretch-activated cation channels (SAC) are present in intact human umbilical vein endothelium (HUVE) and in an endothelial cell line (EA.hy) and whether they act as endothelial mechanosensors, and to determine whether endothelial SAC in HUVE from women with pregnancies complicated by preeclampsia undergo functional changes compared with those in HUVE from women with normotensive pregnancies. METHODS AND RESULTS: By use of the patch-clamp technique we identified a SAC in intact HUVE and in an endothelial cell line. The SAC had mean conductances of 29+/-5 pS (n = 38) for K+ and 12+/-2 pS (n = 4) for Ca2+. Administration of 50 micromol/I gadolinium, a blocker of mechanosensitive ion channels, completely blocked activity of this channel. We found from single-channel recordings that influx of Ca2+ through SAC directly activated high-conductance Ca2+-dependent potassium channels, proving that a significant influx of Ca2+ through SAC occurs at physiologic concentrations of Ca2+. In a comparative study, apparent channel density of SAC (percentage of patches with SAC activity) in HUVE from women with pregnancies complicated by preeclampsia (36.2 +/- 4.3%) was twofold higher than that in HUVE from women with normal pregnancies (17.9+/-2.9%, P< 0.01). Channel conductance and sensitivity to stretching of SAC were not altered by preeclampsia. CONCLUSIONS: Since SAC are capable of acting as endothelial mechanosensors, the greater than normal density of SAC associated with preeclampsia might reflect an alteration of mechanotransduction.

Adult↗
PubMed1997

Prospective evaluation of pretransplant blood transfusions in cadaver kidney recipients.

BACKGROUND: A beneficial effect of pretransplant transfusions on graft survival was demonstrated in the early 1970s. In the mid-1980s, however, retrospective studies showed that transfusions had lost their graft-protective effect in the cyclosporine era. During the last 10 years, deliberate transfusion pretreatment of transplant patients has been discontinued. METHODS: Within a collaborative project of 14 transplant centers, prospective recipients of cadaver kidney grafts were randomized to receive either three pretransplant transfusions or transplants without transfusions. RESULTS; The graft survival rate was significantly higher in the 205 transfusion recipients than in the 218 patients who did not receive transfusions (at 1 year: 90+/-2% vs. 82+/-3%, P=0.020; at 5 years: 79+/-3% vs. 70+/-4%, P=0.025). Cox regression analysis showed that this effect was independent of age, gender, underlying disease, prophylaxis with antilymphocyte antibodies, and preformed lymphocytotoxins. CONCLUSIONS; Transfusion pretreatment improves the outcome of cadaver kidney transplants even with the use of modern immunosuppressive regimens.

Blood Transfusion↗
PubMed1997

Laparoscopy in renal transplant patients.

OBJECTIVES: To evaluate the use of laparoscopic techniques in patients with a renal transplant. METHODS: Since 1992, 358 patients have undergone urologic laparoscopy at our hospital. Among these, 37 procedures (10.4%) were performed in patients with a renal transplant: 14 bilateral nephrectomies for severe drug-resistant hypertension, 9 marsupializations of symptomatic lymphoceles, 6 renal allograft biopsies in patients with clotting abnormalities, 6 unilateral nephrectomies, and 2 nephroureterectomies for recurrent episodes of pyelonephritis and symptomatic vesicoureteral reflux, respectively. RESULTS: Five complications (14%) and three conversions (8%) occurred. Patients who underwent successful laparoscopic operations began mobilization and oral intake on the day after the operation. The hospital stay ranged from 1 to 6 days. In the nephrectomy groups, perioperative urine outputs remained stable and post-operative urine outputs were increased as compared with those in the perioperative period (P < 0.05). Post-operatively, serum creatinine remained stable or improved in patients who underwent nephrectomy or marsupialization of lymphocele. CONCLUSIONS: Our results indicate that laparoscopic techniques are safe and effective in the treatment of patients with a renal transplant. Renal allograft function apparently is not affected by laparoscopic procedures.

Adult↗
PubMed1997

Mechanosensitive cation channels in aortic endothelium of normotensive and hypertensive rats.

In response to humoral and hemodynamic stimuli, vascular endothelium regulates vascular tone by releasing endothelium-derived vasoactive factors. Stretch-activated cation channels have been postulated to act as endothelial mechanosensors that respond to changes in hemodynamic forces. We report the presence of a nonselective (n=98) and K+-selective (n=53) stretch-activated channel in rat intact aortic endothelium and isolated aortic endothelial cells. The nonselective channel showed a permeability ratio for Na+, K+, and Ca2+ of 1:0.95:0.23 and was completely blocked by 50 micromol/L gadolinium, a blocker of stretch-activated channels. The K+-selective channel was selectively permeable for K+, with a K+-Na+ permeability ratio of 10.9:1. In whole-cell current recordings, hyposmotic cell swelling induced an increase in cell conductance. The swelling-induced current was completely blocked by 50 micromol/L gadolinium, showing that stretch-activated channels were activated by cell swelling and carry macroscopic cell currents. In a comparative study with normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), the K+-selective stretch-activated channel was observed in a 4.4-fold higher density in adult SHR compared with WKY. Also, in adult SHR, the stretch sensitivity of the nonselective channel was nearly twice as high as in WKY. In contrast, channel properties were unchanged in young SHR (5 to 6 weeks old) compared with age-matched WKY. These data suggest that stretch-activated channels are regulated in their sensitivity and density when subjected to increased hemodynamic forces such as in hypertension. Since the channels are capable of acting as endothelial mechanosensors, the altered channel properties might contribute to an altered mechanoreception in hypertension.

Age Factors↗
PubMed1997

[Does preoperative corticoid administration reduce the incidence of acute rejections after kidney transplantation?].

Primary immunosuppressive therapy in renal transplantation is mediated by glucocorticosteroids with a delay of several hours. Consequence of the common practice of using first dose of steroids intraoperatively is a first contact of antigens with an unaltered immune system. In a prospective study on 111 renal transplant patients, we could show by the parameters of in vitro cytokine generation and acute rejection episodes that immunological responsiveness can be altered by early (5 h) preoperative use of glucocorticosteroids.

Adult↗
PubMed1997

[Laparoscopic staged lavage in CAPD catheter peritonitis--an alternative to open treatment?].

Three patients suffering from severe CAPD peritonitis underwent laparoscopically programmed lavage after removal of the catheter. After an average of four laparoscopic lavage operations all patients had to be treated using conventional open procedures; a mean of ten programmed lavage procedures were carried out because of increasing peritoneal inflammation and worsening of the clinical situation during minimal invasive therapy. One patient did not survive. Laparoscopic treatment is thus not recommended for diffuse peritonitis.

Adult↗
PubMed1996

Up-regulation of pressure-activated Ca(2+)-permeable cation channel in intact vascular endothelium of hypertensive rats.

In endothelial cells, stretch-activated cation channels have been proposed to act as mechanosensors for changes in hemodynamic forces. We have identified a novel mechanosensitive pressure-activated channel in intact endothelium from rat aorta and mesenteric artery. The 18-pS cation channel responded with a multifold increase in channel activity when positive pressure was applied to the luminal cell surface with the patch pipette and inactivated at negative pipette pressure. Channel permeability ratio for K+, Na+, and Ca2+ ions was 1:0.98:0.23. Ca2+ influx through the channel was sufficient to activate a neighboring Ca2(+)-dependent K+ channel. Hemodynamic forces are chronically disturbed in arterial hypertension. Endothelial cell dysfunction has been implicated in the pathogenesis of arterial hypertension. In two comparative studies, density of the pressure-activated channel was found to be significantly higher in spontaneously hypertensive rats and renovascular hypertensive rats compared with their respective normotensive controls. Channel activity presumably leads to mechanosensitive Ca2+ influx and induces cell hyperpolarization by K+ channel activity. Both Ca2+ influx and hyperpolarization are known to induce a vasodilatory endothelial response by stimulating endothelial nitric oxide (NO) production. Up-regulation of channel density in hypertension could, therefore, represent a counterregulatory mechanism of vascular endothelium.

Animals↗