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The early steps of the Mg(2+)-ATPase activity of relaxed rabbit psoas myofibrils were studied in a buffer of near-physiological ionic strength at 4 degrees C by the rapid flow quench technique. The initial ATP binding steps were studied by the ATP chase, and the cleavage and release of product steps by the Pi burst method. The data obtained were interpreted(More)
2,3-Butanedione monoxime (BDM) reversibly inhibits force production in muscle. At least part of its action appears to be directly on the contractile apparatus. To understand better its mechanism of action, we studied the effect of BDM on the steps of myosin subfragment 1 Mg(2+)-ATPase in 0.1 M potassium acetate, pH 7.4. Because of the rapidity of certain(More)
In previous work, we studied the early steps of the Mg(2+)-ATPase activity of Ca(2+)-activated myofibrils [Houadjeto, M., Travers, F., & Barman, T. (1992) Biochemistry 31, 1564-1569]. The myofibrils were free to contract, and the results obtained refer to the ATPase cycle of myofibrils contracting with no external load. Here we studied the ATPase of(More)
Our objective was to determine a good in vitro model for muscle fiber ATPase, and we compared the kinetics of Ca(2+)-activated myofibrils and cross-linked actoS1 in a buffer of physiological ionic strength. The myofibrils were cross-linked chemically to mimic the isometric condition of fibers or were un-cross-linked (the isotonic condition), and temperature(More)
A number of agents that inhibit oxidative phosphorylation by different mechanisms (carbonyl cyanide mchlorophenylhydrazone [CCCP], sodium azide, oligomycin) induced an increase of cytoplasmic Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells, as measured by microfluorimetry with digital imaging. All three agents are known inhibitors of insulin(More)
We present a method for obtaining lab-quality measurements of pointing performance from unobtrusive observations of natural in situ interactions. Specifically, we have developed a set of user-independent classifiers for discriminating between deliberate, targeted mouse pointer movements and those movements that were affected by any extraneous factors. To(More)
Experiments with inside-out patches excised from pancreatic B-cells have yielded evidence that mitochondria are often contained in the cytoplasmic plug protruding into the tip of patch pipette. When intact B-cells were loaded with the fluorescent mitochondrial stain, rhodamine 123, and membrane patches excised from these cells, a green fluorescence could be(More)
To elucidate the beta-cytotropic effect of imidazoline compounds their inhibitory effect on ATP-dependent K+ channels (K(ATP) channels) in pancreatic B-cells was compared with their binding to membranes from insulin-secreting HIT T15 cells. K(ATP) channels in inside-out patches from B-cells were closed with the following rank order of efficacy at 10 microM:(More)
Phentolamine, an alpha-adrenoceptor-blocking agent with an imidazoline structure, induces an increase in the cytoplasmic Ca2+ concentration of pancreatic B-cells. This effect occurs at a concentration (32 microM) at which phentolamine is able to enhance glucose-induced insulin secretion. The increase in cytoplasmic Ca2+ concentration caused by phentolamine(More)
The inhibitory effect of P3-[1-(2-nitrophenyl)ethyl]adenosine 5'-triphosphate (caged ATP) on the binding of Mg2+-ATP to myofibrils was investigated. The most sensitive method was found to be the monitoring of single turnovers of [gamma-32P] ATP hydrolysis using the quench flow technique. The method was tested using ADP, which was found to have an inhibition(More)