How to Compute Spectra with Error Control.

Computing the spectra of operators is a fundamental problem in the sciences, with wide-ranging applications in condensed-matter physics, quantum mechanics and chemistry, statistical mechanics, etc. While there are algorithms that in certain cases converge to the spectrum, no general procedure is known that (a) always converges, (b) provides bounds on the errors of approximation, and (c) provides approximate eigenvectors. This may lead to incorrect simulations.

Organotypic slice culture from human adult ventricular myocardium.

Aims: Cardiovascular research requires complex and functionally intact experimental models. Due to major differences in the cellular and subcellular composition of the myocardium between species, the use of human heart tissue is highly desirable. To enhance the experimental use of the human myocardium, we established methods for the preparation of vital tissue slices from the adult ventricular myocardium as well as conditions for their long-term preservation in organotypic culture.

Effect of dronedarone on Na+, Ca2+ and HCN channels.

Previous studies showed that amiodarone causes state-dependent inhibition of Na(+) channels thereby mediating an atrial-selective drug effect. The aim of the present study was to investigate the impact of the new antiarrhythmic compound dronedarone on Na(+), Ca(2+) and hyperpolarization-activated cyclic nucleotide-gated ion channels. Monophasic action potentials (MAP) and effective refractory period (ERP) were studied in arterially perfused left atria and ventricular wedge preparations of the pig.

Epithelial Na+ channels derived from human lung are activated by shear force.

During breathing the pulmonary epithelial cells are permanently exposed to physical forces and shear force (SF) in particular. In our present study we questioned whether the lung epithelial Na(+) channel (hENaC) responds to shear force. For this purpose ENaC was cloned from human lung tissue, expressed in Xenopus oocytes and functionally characterized by electrophysiological techniques.

Impact of mechanical stress on ion transport in native lung epithelium (Xenopus laevis): short-term activation of Na+, Cl (-) and K+ channels.

Epithelia, in general, and the lung epithelium, in particular, are exposed to mechanical forces, but little is known about their impact on pulmonary ion transport. In our present study, we employed transepithelial ion transport measurements on Xenopus lung preparations using custom-built Ussing chambers. Tissues were exposed to mechanical stress by increasing the water column (5 cm) at one side of the tissues.

CFTR-dependent Cl- secretion in Xenopus laevis lung epithelium.

In our present study we used preparations from Xenopus laevis lungs to perform electrophysiological Ussing chamber measurements, unidirectional flux measurements, and employed molecular approaches to elucidate the presence and function of a cystic fibrosis transmembrane conductance regulator (CFTR) homolog in this tissue. Application of different CFTR blockers (NPPB (5-nitro-2-(3-phenylpropylamino)benzoic acid), niflumic acid (NFA), glibenclamide, lonidamine, CFTR(inh)-172) to the apical side of the tissues was able to significantly decrease the measured short circuit current (I(SC)) indicating a Cl(-) secretion due to luminal located CFTR channels. This was further supported by a net (36)Cl(-) secretion determined by radioactive tracer flux experiments.

Mechano-sensitivity of epithelial sodium channels (ENaCs): laminar shear stress increases ion channel open probability.

Epithelial cells are exposed to a variety of mechanical forces, but little is known about the impact of these forces on epithelial ion channels. Here we show that mechanical activation of epithelial sodium channels (ENaCs), which are essential for electrolyte and water balance, occurs via an increased ion channel open probability. ENaC activity of heterologously expressed rat (rENaC) and Xenopus (xENaC) orthologs was measured by whole-cell as well as single-channel recordings.

Short-term exposure to waterborne free silver has acute effects on membrane current of Xenopus oocytes.

Waterborne free silver can cause osmo- and ionoregulatory disturbances in freshwater organisms. The effects of a short-term exposure to extracellular Ag+ ions on membrane currents were investigated in voltage-clamped defolliculated Xenopus oocytes. At a holding potential of -60 mV, ionic silver (1 microM Ag+) increased inward currents (=I(Ag)) from -8+/-2 nA to -665+/-41 nA (n=74; N=27).