Vascular endothelial cells are constantly exposed to mechanical forces resulting from blood flow and transmural pressure. The goal of this study was to determine whether mechanical stimulation alters the properties of endothelial voltage-gated K+ channels. Cardiac microvascular endothelial cells (CMECs) were isolated from rat ventricular muscle and cultured on thin sheets of silastic membranes. Membrane currents were measured with the use of the whole-cell arrangement of the patch-clamp technique in endothelial cells subjected to static stretch for 24 hours and compared with measurements from control, nonstretched cells. Voltage steps positive to -30 mV resulted in the activation of a time-dependent, delayed rectifier K+current (IK) in the endothelial cells. Mechanically induced increases of 97%, 355%, and 106% at +30 mV were measured in the peak amplitude of IK in cells stretched for 24 hours by 5%, 10%, and 15%, respectively. In addition, the half-maximal voltage required for IK activation was shifted from +34 mV in the nonstretched cells to -5 mV in the stretched cells. Although IK in both groups of CMECs was blocked to a similar extent by tetraethylammonium, currents in the stretched endothelial cells displayed an enhanced sensitivity to inhibition by charybdotoxin. Preincubation of the CMECs with either pertussis toxin or phorbol 12-myristate 13-acetate during the 24 hours of cell stretch did not prevent the increase in IK. The application of phorbol 12-myristate 13-acetate and static stretch stimulated the proliferation of CMECs. Stretch-induced regulation of K+ channels may be important to control the resting potential of the endothelium and may contribute to capillary growth during periods of mechanical perturbation. (+info)
Validation of haemodialysis recirculation and access blood flow measured by thermodilution.
BACKGROUND: Recirculation (R) and access blood flow (Qac) measurements are considered useful indicators of adequate delivery of haemodialysis. It was the purpose of this study to compare measurements of R and Qac obtained by two different techniques which are based on the same principle of indicator dilution, but which differ because of the characteristics of the injection and detection of the different indicators used. METHODS: Recirculation measured by a thermal dilution technique using temperature sensors (BTM, Fresenius Medical Care) was compared with recirculation measured by a validated saline dilution technique using ultrasonic transducers placed on arterial and venous segments of the extracorporeal circulation (HDM, Transonic Systems, Inc.). Calculated access flows were compared by Bland Altman analysis. Data are given as mean +/- SD. RESULTS: A total of 104 measurements obtained in 52 treatments (17 patients, 18 accesses) were compared. Recirculation measured with correct placement of blood lines and corrected for the effect of cardiopulmonary recirculation using the 'double recirculation technique' was -0.02 +/- 0.14% by the BTM technique and not different from the 0% measured by the HDM technique. Recirculation measured with reversed placement of blood lines and corrected for the effect of cardiopulmonary recirculation was 19.66 +/- 10.77% measured by the BTM technique compared with 20.87 +/- 11.64% measured by the HDM technique. The difference between techniques was small (-1.21 +/- 2.44%) albeit significant. Access flow calculated from BTM recirculation was 1328 +/- 627 ml/min compared with 1390 +/- 657 ml/min calculated by the HDM technique. There was no bias between techniques. CONCLUSION: BTM thermodilution yields results which are consistent with the HDM ultrasound dilution technique with regard to both recirculation and access flow measurement. (+info)
Surfactant protein A enhances the binding and deacylation of E. coli LPS by alveolar macrophages.
Surfactant protein (SP) A and SP-D are involved in multiple immunomodulatory functions of innate host defense partly via their interaction with alveolar macrophages (AMs). In addition, both SP-A and SP-D bind to bacterial lipopolysaccharide (LPS). To investigate the functional significance of this interaction, we first tested the ability of SP-A and SP-D to enhance the binding of tritium-labeled Escherichia coli LPS to AMs. In contrast to SP-D, SP-A enhanced the binding of LPS by AMs in a time-, temperature-, and concentration-dependent manner. Coincubation with surfactant-like lipids did not affect the SP-A-mediated enhancement of LPS binding. At SP-A-to-LPS molar ratios of 1:2-1:3, the LPS binding by AMs reached 270% of control values. Second, we investigated the role of SP-A in regulating the degradation of LPS by AMs. In the presence of SP-A, deacylation of LPS by AMs increased by approximately 2.3-fold. Pretreatment of AMs with phosphatidylinositol-specific phospholipase C had no effect on the SP-A-enhanced LPS binding but did reduce the amount of serum-enhanced LPS binding by 50%, suggesting that a cell surface molecule distinct from CD14 mediates the effect of SP-A. Together the results for the first time provide direct evidence that SP-A enhances LPS binding and degradation by AMs. (+info)
Long-term culture of human CD34(+) progenitors with FLT3-ligand, thrombopoietin, and stem cell factor induces extensive amplification of a CD34(-)CD14(-) and a CD34(-)CD14(+) dendritic cell precursor.
Current in vitro culture systems allow the generation of human dendritic cells (DCs), but the output of mature cells remains modest. This contrasts with the extensive amplification of hematopoietic progenitors achieved when culturing CD34(+) cells with FLT3-ligand and thrombopoietin. To test whether such cultures contained DC precursors, CD34(+) cord blood cells were incubated with the above cytokines, inducing on the mean a 250-fold and a 16,600-fold increase in total cell number after 4 and 8 weeks, respectively. The addition of stem cell factor induced a further fivefold increase in proliferation. The majority of the cells produced were CD34(-)CD1a- CD14(+) (p14(+)) and CD34(-)CD1a-CD14(-) (p14(-)) and did not display the morphology, surface markers, or allostimulatory capacity of DC. When cultured with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4), both subsets differentiated without further proliferation into immature (CD1a+, CD14(-), CD83(-)) macropinocytic DC. Mature (CD1a+, CD14(-), CD83(+)) DCs with high allostimulatory activity were generated if such cultures were supplemented with tumor necrosis factor-alpha (TNF). In addition, p14(-) cells generated CD14(+) cells with GM-CSF and TNF, which in turn, differentiated into DC when exposed to GM-CSF and IL-4. Similar results were obtained with frozen DC precursors and also when using pooled human serum AB+ instead of bovine serum, emphasizing that this system using CD34(+) cells may improve future prospects for immunotherapy. (+info)
Low-molecular weight heparin restores in-vitro trophoblast invasiveness and differentiation in presence of immunoglobulin G fractions obtained from patients with antiphospholipid syndrome.
The present study was designed to investigate the effects of immunoglobulin G obtained from patients with antiphospholipid syndrome (APS) on in-vitro models of trophoblast invasiveness and differentiation. We tested the binding of affinity-purified immunoglobulin G to human primary trophoblast cells. These antibodies affected the invasiveness and differentiation of cytotrophoblast cells after binding to the cell surface. In addition, we determined whether the drugs used to treat APS might be able to restore the trophoblast functions. Low-molecular weight heparin, in a dose-dependent manner, significantly reduced the immunoglobulin G binding to trophoblast cells and restored in-vitro placental invasiveness and differentiation. No effect was observed in the presence of acetylsalicylic acid. These observations may help in understanding the role of these treatments in women with APS. (+info)
Partial characterization of apoptotic factor in Alzheimer plasma.
We have previously demonstrated that a plasma natriuretic factor is present in Alzheimer's disease (AD), but not in multi-infarct dementia (MID) or normal controls (C). We postulated that the natriuretic factor might induce the increased cytosolic calcium reported in AD by inhibiting the sodium-calcium antiporter, thereby activating the apoptotic pathway. To test for a factor in AD plasma that induces apoptosis, we exposed nonconfluent cultured LLC-PK1 cells to plasma from AD, MID, and C for 2 h and performed a terminal transferase-dUTP-nick-end labeling (TUNEL) assay. The plasma from AD increased apoptosis nearly fourfold compared with MID and C. The effect was dose dependent and the peak effect was attained after a 2-h exposure. Additionally, apoptotic morphology was detected by electron microscopy, and internucleosomal DNA cleavage was found. We inhibited apoptosis by removing calcium from the medium, inhibiting protein synthesis with cycloheximide, alternately boiling or freezing and thawing the plasma, and digesting a partially purified fraction with trypsin. Heating AD plasma to 56 degrees C did not deactivate the apoptotic factor. These results demonstrate the presence of an apoptotic factor in the plasma of patients with AD. (+info)
Delayed ischemic preconditioning is mediated by opening of ATP-sensitive potassium channels in the rabbit heart.
Cardioprotection from preconditioning reappears 24 h after the initial stimulus. This phenomenon is called the second window of protection (SWOP). We hypothesized that opening of the ATP-sensitive potassium (KATP) channel mediates the protective effect of SWOP. Rabbits were preconditioned (PC) with four cycles of 5-min regional ischemia each followed by 10 min of reperfusion. Twenty-four hours later, the animals were subjected to sustained ischemia for 30 min followed by 180 min of reperfusion (I/R). Glibenclamide (Glib, 0.3 mg/kg ip) or 5-hydroxydecanoate (5-HD, 5 mg/kg iv) was used to block the KATP channel function. Infarct size was reduced from 41.2 +/- 2. 6% in sham-operated rabbits to 11.6 +/- 1.0% in PC rabbits, a 71% reduction (n = 11, P < 0.01). Treatment with Glib or 5-HD before I/R increased the infarct size to 43.4 +/- 2.6 and 37.8 +/- 1.9%, respectively (P < 0.01 vs. PC group, n = 12/group). Sham animals treated with either Glib or 5-HD had an infarct size of 39.0 +/- 3.4 and 37.8 +/- 1.5%, respectively, which was not different from control (40.0 +/- 3.8%) or sham (41.2 +/- 2.6%) I/R hearts. Monophasic action potential duration (APD) at 50% repolarization significantly shortened by 28.7, 26.6, and 23.3% in sham animals during 10, 20, and 30 min of ischemia. However, no further augmentation in the shortening of APD was observed in PC hearts. Glib and 5-HD significantly suppressed ischemia-induced epicardial APD shortening, suggesting that 5-HD may not be a selective blocker of the mitochondrial KATP channel in vivo. We conclude that SWOP is mediated by a KATP channel-sensitive mechanism that may have occurred because of the opening of the sarcolemmal KATP channel in vivo. (+info)
Evidence of splanchnic-brain signaling in inhibition of ingestive behavior by middle molecules.
Anorexia, nausea, and vomiting are common symptoms of uremic intoxication. Fractions in the middle molecule weight range, isolated from normal urine and uremic plasma ultrafiltrate, inhibit ingestive behavior in the rat. To investigate their site of action and specificity, male rats were injected intraperitoneally, intravenously, or intracerebroventricularly with concentrated fractions of uremic plasma ultrafiltrate or normal urine (molecular weight range: 1.0 to 5.0 kD) and tested for ingestive and sexual behavior. An intraperitoneal injection of 0.5 ml of urine fraction (10:1) or 2.0 ml of uremic plasma ultrafiltrate fraction (25:1) inhibited carbohydrate intake by 76.3 and 45.9%, respectively, but an intravenous injection had no effect. However, intravenous injection of higher doses inhibited carbohydrate ingestion. An intracerebroventricular injection of 5 or 10 microl of urine (20:1) middle molecule fraction inhibited carbohydrate intake by 13.4 and 41.6%, respectively. An injection of 5 or 10 microl of uremic plasma ultrafiltrate (125:1) middle molecule fraction inhibited carbohydrate intake by 22.6 and 49.5%, respectively. Injections of the corresponding fraction from normal plasma ultrafiltrate had no effect. Injection of urine or uremic plasma ultrafiltrate middle molecule fractions did not affect the display of sexual behavior. These results suggest that middle molecule fractions from uremic plasma ultrafiltrate or normal urine act in the splanchnic region and/or brain to inhibit food intake and that the effect is specific for ingestive behavior. (+info)