Neural control exploits changing mechanical advantage and context dependence to generate different feeding responses in <Emphasis Type="Italic">Aplysia</Emphasis>

How does neural control reflect changes in mechanical advantage and muscle function? In the Aplysia feeding system a protractor muscle's mechanical advantage decreases as it moves the structure that grasps food (the radula/odontophore) in an anterior direction. In contrast, as the radula/odontophore is moved forward, the jaw musculature's mechanical advantage shifts so that it may act to assist forward movement of the radula/odontophore instead of pushing it posteriorly. To test whether the jaw musculature's context-dependent function can compensate for the falling mechanical advantage of the protractor muscle, we created a kinetic model of Aplysia's feeding apparatus. During biting, the model predicts that the reduction of the force in the protractor muscle I2 will prevent it from overcoming passive forces that resist the large anterior radula/odontophore displacements observed during biting. To produce protractions of the magnitude observed during biting behaviors, the nervous system could increase I2's contractile strength by neuromodulating I2, or it could recruit the I1/I3 jaw muscle complex. Driving the kinetic model with in vivo EMG and ENG predicts that, during biting, early activation of the context-dependent jaw muscle I1/I3 may assist in moving the radula/odontophore anteriorly during the final phase of protraction. In contrast, during swallowing, later activation of I1/I3 causes it to act purely as a retractor. Shifting the timing of onset of I1/I3 activation allows the nervous system to use a mechanical equilibrium point that allows I1/I3 to act as a protractor rather than an equilibrium point that allows I1/I3 to act as a retractor. This use of equilibrium points may be similar to that proposed for vertebrate control of movement.     

Cystathionine pathway-dependent cytotoxicities of diethyl maleate and diamide in rat and human hepatoma-derived cell cultures

Glutathione (GSH) plays a role in many toxicologically important metabolic processes. It was previously established that L-buthionine S,R-sulphoximine (BSO), a specific inhibitor of (- glutamylcysteine synthetase, reduces the GSH content more efficiently in rat (Fa32) than in human (HEp-G2) hepatoma-derived cells. We therefore investigated whether the cystathionase inhibitor propargylglycine (PPG) could further decrease the BSO-induced GSH depletion in HEp-G2 cells. The influence of the cystathionine precursors N-acetylmethionine, methionine and homocysteine on the cytotoxicity of diethyl maleate (DEM) and diamide [1,1'-azobis(N,N-dimethylformamide)] was also investigated. PPG reduced the GSH content in both cell lines. A further GSH decrease in HEp-G2 was obtained when using a BSO + PPG combination containing relatively high concentrations of PPG. BSO diminished the toxicity of PPG. Homocysteine was the most efficacious of the tested cystathionine precursors in increasing the GSH content and reducing the cytotoxicity of DEM and diamide in Fa32 and HEp-G2 cells.     

A New Formulation of Calcitriol (DN-101) for High-Dose Pulse Administration in Prostate Cancer Therapy

Although the antineoplastic activity of calcitriol in prostate cancer has been known for many years, the agent's use in oncology has been prevented because of the occurrence of hypercalcemia with daily administration. High-dose pulse administration of calcitriol has the potential to improve the therapeutic index of calcitriol. Results of a phase II study of calcitriol and docetaxel (Taxotere(R)) suggest that this combination may have utility in androgen-independent prostate cancer (AIPC). DN-101, a high-dose (15 mug) formulation of calcitriol suitable for use in oncology, is now being tested in a randomized trial (AIPC Study of Calcitriol Enhancing Taxotere). This formulation of calcitriol could become an important new tool for improving the efficacy of docetaxel in the treatment of AIPC and would join the ranks of other nuclear receptor ligands in cancer treatment. Investigations of DN-101 in the treatment of a broad range of tumor types and in combination with a variety of agents are an exciting new area of research.     

Overexpression of secretory phospholipase A(2) causes rapid catabolism and altered tissue uptake of high density lipoprotein cholesteryl ester and apolipoprotein A-I

Plasma levels of high density lipoprotein (HDL) cholesterol and its major protein component apolipoprotein (apo) A-I are significantly reduced in both acute and chronic inflammatory conditions, but the basis for this phenomenon is not well understood. We hypothesized that secretory phospholipase A(2) (sPLA(2)), an acute phase protein that has been found in association with HDL, promotes HDL catabolism. A series of HDL metabolic studies were performed in transgenic mice that specifically overexpress human sPLA(2) but have no evidence of local or systemic inflammation. We found that HDL isolated from these mice have a significantly lower phospholipid and cholesteryl ester and significantly greater triglyceride content. The fractional catabolic rate (FCR) of (125)I-HDL was significantly faster in sPLA(2) transgenic mice (4.08 +/- 0.01 pools/day) compared with control wild-type littermates (2.16 +/- 0.48 pools/day). (125)I-HDL isolated from sPLA(2) transgenic mice was catabolized significantly faster than (131)I-HDL isolated from wild-type mice after injection in wild-type mice (p < 0.001). Injection of (125)I-tyramine-cellobiose-HDL demonstrated significantly greater degradation of HDL apolipoproteins in the kidneys of sPLA(2) transgenic mice compared with control mice (p < 0.05). The fractional catabolic rate of [(3)H]cholesteryl ether HDL was significantly faster in sPLA(2)-overexpressing mice (6.48 +/- 0.24 pools/day) compared with controls (4.80 +/- 0.72 pools/day). Uptake of [(3)H] cholesteryl ether into the livers and adrenals of sPLA(2) transgenic mice was significantly enhanced compared with control mice. In summary, these data demonstrate that overexpression of sPLA(2) alone in the absence of inflammation causes profound alterations of HDL metabolism in vivo and are consistent with the hypothesis that sPLA(2) may promote HDL catabolism in acute and chronic inflammatory conditions.     

Preparation and characterization of 'heparinocytes': erythrocytes with covalently bound low molecular weight heparin

In an attempt to create the possibility of stable, long acting, intravascular anticoagulation, low molecular weight heparin was modified by introducing a sulfhydryl group into the molecule (LMWH-SH). Human erythrocytes were covalently grafted with LMWH-SH by the use of a heterobifunctional coupling reagent which reacts with the SH group of LMWH-SH and surface exposed amino groups of erythrocytes now called 'heparinocytes' (HC). HC were morphologically indistinguishable from untreated erythrocytes and displayed identical osmotic resistance. The functionality of HC was analyzed by classical coagulation tests in which they dose dependently inhibited clot formation. HC were also functional in recalcified whole blood inhibiting thrombin formation as assessed by the cleavage of the chromogenic substrate S-2238. The system appears applicable as a potential autologous, long-term anticoagulant treatment or prophylaxis.     

Microsensors as a tool to determine chemical microgradients and bacterial activity in wastewater biofilms and flocs

Microsensors used in microbial ecology are reviewed with emphasis on new sensor developments (NO₃ ^-, NO₂ ^-, NH₄ ⁺, CO₂, H₂, H₂S and CH₄ microsensors as well as fiberoptical microsensors for O₂, temperature and pH). Examples of microsensor applications in biofilms and activated sludge flocs are presented, where sulfate reduction and denitrification were studied.     

Gene expression in Xenopus oocytes

1. Gene expression in Xenopus oocytes is now an integral part of many molecular cloning strategies. 2. For some genes, such as those encoding the ion channels, this system has emerged as the only available means to authenticate and examine the biological activities of the cloned DNA. 3. This review discusses some of the current applications of Xenopus oocytes in modern molecular biology.