Magnetic resonance perfusion of the myocardium: semiquantitative and quantitative evaluation in comparison with coronary angiography and fractional flow reserve.

PURPOSE: The aim of this study was to investigate if a quantitative evaluation of a magnetic resonance (MR) perfusion examination of the myocardium can achieve a comparable diagnostic accuracy as a semiquantitative evaluation. METHODS: A total of 31 patients with suspected coronary artery disease underwent MR imaging and conventional coronary angiography. Stenoses with a diameter reduction between 50% and 75% were evaluated by an intracoronary pressure wire examination (fractional flow reserve) for assessment of their hemodynamic relevance. A 0.05 mmol/kg contrast material bolus (gadopentetate dimeglumine) was applied during adenosine-induced stress (140 µg/kg/min) and at rest with a flow rate of 5 mL/s. Signal intensity time curves of the first-pass MR perfusion images, acquired at rest and under adenosine stress with a Saturation Recovery-turbo Fast Low Angle Shot Magnetic Resonance Imaging sequence, were analyzed by Argus Dynamic Signal Analysis (Siemens Healthcare, Erlangen, Germany). For the semiquantitative evaluation, the upslope value of a linear fit from the foot point to the signal maximum was calculated for 18 segments (signal intensity units per second). For the quantitative evaluation, a model-independent deconvolution was used to calculate coronary blood flow (MBF in mL/100 g/min). For each segment for the stress and rest examination, upslope value and MBF were determined. In addition, the ratio of the stress and rest value for each segment was determined (myocardial perfusion reserve index [MPRI]). The mean value of the 2 segments with the lowest value was calculated for each patient. Coronary artery stenosis greater than 75% or greater than 50% with positive fractional flow reserve less than 0.75 was considered as hemodynamically relevant. Receiver-operator-curves were calculated. RESULTS: The values of the area under the ROC curves were 0.74, 0.66, and 0.92 for the US(Stress), US(Rest), and US(MPRI) evaluations (semiquantitative evaluation). The values for the MBF(Stress), MBF(Rest), and MBF(MPRI) evaluations (quantitative evaluation) were 0.92, 0.68, and 0.84, respectively. Comparing US(MPRI) and MBF(Stress), identical values and no significant difference were found for the area under the ROC curves. CONCLUSION: A quantitative evaluation using a model-free deconvolution provides identical diagnostic performance when only a stress examination is used, much similar to a semiquantitative evaluation, if both stress and rest examinations are used.

Buffer-dependent regulation of aquaporin-1 expression and function in human peritoneal mesothelial cells.

BACKGROUND: Biocompatible peritoneal dialysis fluids (PDF) are buffered with lactate and/or bicarbonate. We hypothesized that the reduced toxicity of the biocompatible solutions might unmask specific effects of the buffer type on mesothelial cell functions. METHODS: Human peritoneal mesothelial cells (HPMC) were incubated with bicarbonate (B-)PDF or lactate-buffered (L-)PDF followed by messenger RNA (mRNA) and protein analysis. Gene silencing was achieved using small interfering RNA (siRNA), functional studies using Transwell culture systems, and monolayer wound-healing assays. RESULTS: Incubation with B-PDF increased HPMC migration in the Transwell and monolayer wound-healing assay to 245 ± 99 and 137 ± 11% compared with L-PDF. Gene silencing showed this effect to be entirely dependent on the expression of aquaporin-1 (AQP-1) and independent of AQP-3. Exposure of HPMC to B-PDF increased AQP-1 mRNA and protein abundance to 209 ± 80 and 197 ± 60% of medium control; the effect was pH dependent. L-PDF reduced AQP-1 mRNA. Addition of bicarbonate to L-PDF increased AQP-1 abundance by threefold; mRNA half-life remained unchanged. Immunocytochemistry confirmed opposite changes of AQP-1 cell-membrane abundance with B-PDF and L-PDF. CONCLUSIONS: Peritoneal mesothelial AQP-1 abundance and migration capacity is regulated by pH and buffer agents used in PD solutions. In vivo studies are required to delineate the impact with respect to long-term peritoneal membrane integrity and function.

Chloride and bicarbonate have similar affinities to the intestinal anion exchanger DRA (down regulated in adenoma).

DRA (down regulated in adenoma, SLC26A3) is an anion exchanger that mediates electroneutral NaCl absorption in the ileum and proximal colon together with NHE3 (Na/H exchanger isoform 3), and that is involved in duodenal and possibly pancreatic bicarbonate secretion. Thus, its chloride and bicarbonate affinities are important for both processes. [Cl]i and pHi transients were measured using MQAE and BCECF. HEK293 cells stably expressing DRA were exposed to 0 mM Cl at various [HCO3] (9 to 51 mM, at 5% CO2 or 15 to 57 mM, at pH 7.5) to determine the HCO3 affinity. After intracellular Cl depletion, 10, 30, and 90 mM Cl were readded at various [HCO3]s to determine the relative Cl and HCO3 affinities. The k0.5 for extracellular HCO3 is between 18.5 and 32.8 mM. Cl and HCO3 compete with similar affinities for transport by DRA. DRA activity is independent of pHo between 7.0 and 7.75. DRA is activated by alkaline pHi. Competition of Cl and HCO3 does not significantly impair NaCl absorption, because in the ileum and colon, luminal Cl is comparably high. Activation at alkaline pHi supports functional coupling of DRA and NHE3 by the subapical pHi. In the distal pancreatic ductal system, luminal HCO3 is high compared to luminal Cl. Under these conditions, competition of Cl and HCO3 is difficult to reconcile with a role of DRA in Cl reabsorption in exchange for HCO3. Our data, thus, provide indirect evidence against a role of DRA in pancreatic HCO3 secretion.

Molecular examination of the transmembrane requirements of the platelet-derived growth factor beta receptor for a productive interaction with the bovine papillomavirus E5 oncoprotein.

The small transmembrane E5 protein of bovine papillomavirus (BPV) transforms cells by forming a stable complex with and activating the platelet-derived growth factor beta receptor (PDGFbetaR). The E5/PDGFbetaR interaction is thought to involve specific physical contacts between the transmembrane domains of the two proteins. Lys(499) at the extracellular juxtamembrane position and Thr(513) within the transmembrane domain of the PDGFbetaR are required for the interaction and are predicted to contact analogously positioned residues in the E5 protein. Here, mutagenic analysis of the transmembrane region of the PDGFbetaR was performed to further characterize the nature of the E5/PDGFbetaR interaction. We show that the receptor transmembrane domain, with minimal extracellular and intracellular sequence, is sufficient for the interaction. In addition, we provide evidence that the polar nature of Thr(513) as well as its positioning along the transmembrane alpha-helix is important for the interaction. We also identify the receptor transmembrane amino acids Ile(506) and Leu(520) as additional requirements for the interaction. Because Lys(499), Thr(513), Ile(506), and Leu(520) all align along the same face of the predicted PDGFbetaR transmembrane alpha-helix, our data support the model that the PDGFbetaR contacts the E5 protein via multiple amino acids along a single alpha-helical interface.