Sub-cellular Electrical Heterogeneity Revealed by Loose Patch Recording Reflects Differential Localization of Sarcolemmal Ion Channels in Intact Rat Hearts.

The cardiac action potential (AP) is commonly recoded as an integral signal from isolated myocytes or ensembles of myocytes (with intracellular microelectrodes and extracellular macroelectrodes, respectively). These signals, however, do not provide a direct measure of activity of ion channels and transporters located in two major compartments of a cardiac myocyte: surface sarcolemma and the T-tubule system, which differentially contribute to impulse propagation and excitation-contraction (EC) coupling. In the present study we investigated electrical properties of myocytes within perfused intact rat heart employing loose patch recording with narrow-tip (2 µm diameter) extracellular electrodes. Using this approach, we demonstrated two distinct types of electric signals with distinct waveforms (single peak and multi-peak AP; AP1 and AP2, respectively) during intrinsic pacemaker activity. These two types of waveforms depend on the position of the electrode tip on the myocyte surface. Such heterogeneity of electrical signals was lost when electrodes of larger pipette diameter were used (5 or 10 µm), which indicates that the electric signal was assessed from a region of <5 µm. Importantly, both pharmacological and mathematical simulation based on transverse (T)-tubular distribution suggested that while the AP1 and the initial peak of AP2 are predominantly attributable to the fast, inward Na+ current in myocyte's surface sarcolemma, the late components of AP2 are likely representative of currents associated with L-type Ca2+ channel and Na+/Ca2+ exchanger (NCX) currents which are predominantly located in T-tubules. Thus, loose patch recording with narrow-tip pipette provides a valuable tool for studying cardiac electric activity on the subcellular level in the intact heart.

Serum Albumin Binding and Esterase Activity: Mechanistic Interactions with Organophosphates.

The albumin molecule, in contrast to many other plasma proteins, is not covered with a carbohydrate moiety and can bind and transport various molecules of endogenous and exogenous origin. The enzymatic activity of albumin, the existence of which many scientists perceive skeptically, is much less studied. In toxicology, understanding the mechanistic interactions of organophosphates with albumin is a special problem, and its solution could help in the development of new types of antidotes. In the present work, the history of the issue is briefly examined, then our in silico data on the interaction of human serum albumin with soman, as well as comparative in silico data of human and bovine serum albumin activities in relation to paraoxon, are presented. Information is given on the substrate specificity of albumin and we consider the possibility of its affiliation to certain classes in the nomenclature of enzymes.

A novel strategy for the synthesis of thermally stable and apoptosis-inducing 2,3-dihydroazetes.

A general and concise approach to thermally and hydrolytically stable alkyl 2,3-dihydroazete-2,3-di-/2,2,3-tricarboxylates from alkyl 2-bromoazirine-2-carboxylates or 4-bromo-5-alkoxyisoxazoles is reported. The synthesis involves the formation of 2-azabuta-1,3-diene by the reaction of rhodium carbenoid with isoxazole or azirine followed by cyclization/hydrodebromination cascade. The latter reaction is the first example of the selective hydrodehalogenation of a valence isomer under equilibrium conditions. In vitro cytotoxicity tests on THP-1 cell line revealed that the 2,3-dihydroazetes greatly differ in their ability to induce apoptosis and/or necrosis. To adequately describe and quantitatively assess these properties, the difference between the two areas under the curves of concentration dependency of apoptosis/necrosis induction within the concentration range was used. Trimethyl 4-phenyl-2,3-dihydroazete-2,2,3-tricarboxylate was found to display the maximal apoptotic potential coupled with high cytotoxic and minimal necrotic potential.