Platinum for neural stimulation: voltammetry considerations.

The underlying cause of electrical stimulation-induced tissue trauma is debated. Our focus has been to study effects of generating electrochemical by-products at the electrode-electrolyte interface, using the pulse-clamp technique coupled with voltammetry to analyze charge transfer. The platinum-H(2)SO(4) system has been a standard for analyzing electrochemistry on platinum-stimulating electrodes, even though the chemical differences between H(2)SO(4) and the living body are obvious. Experiments were designed to determine whether phosphate-buffered saline (PBS) could serve as a more accurate emulation of living tissue. It had been rumored that platinum's performance in PBS deviates from that in H(2)SO(4) at larger potentials. Voltammetry in PBS was performed in two potential ranges. In a conventional potential range (-0.6 V to +0.9 V versus Ag/AgCl), characteristic peaks appear very similar to published voltammograms of platinum in H(2)SO(4). However, in an extended range (-1.0 V to +1.7 V versus Ag/AgCl), platinum exhibited additional electrochemical activity: one oxidation peak and two reduction peaks. Therefore, voltammetry was performed in NaCl and a sodium phosphate mixture (i.e. PBS components) to separate their activity. The altered electrochemical performance of platinum in PBS suggests that certain reactions on platinum at potentials outside the water window will not reflect what happens in vivo.

Kavain inhibits murine airway smooth muscle contraction.

This study examined the effect of kavain, the principle biologically active component of kava, on murine airway smooth muscle. In isolated isometrically contracted tracheal ring preparations, kavain was noted to diminish the maximal contractile response to both muscarinic receptor activation and voltage-operated calcium channel activation. The IC50 for kavain in rings precontracted with carbachol was found to be 177 microM +/- 53.1, and, in rings precontracted with KCl, it was found to be 59.6 microM +/- 10.1. In addition, pretreatment with kavain attenuated airway smooth muscle contraction evoked with either carbachol or KCl. The EC50 for KCl was not affected by kavain pretreatment. However, the EC50 for carbachol was significantly affected by a high kavain pretreatment dose. Nitric oxide mediated relaxation was not observed to play a role in kavain's smooth muscle relaxing properties. Similarly, prostaglandin pathways are not likely involved in these effects since pretreatment of tracheal rings with indomethacin before carbachol contraction did not reduce the relaxant effect of kavain. The mechanism of kavain-induced relaxation and inhibition of contraction is likely due to a mechanism common to both contractile agonists that were employed in our study.

Chagas' disease in an obstetrical patient.

We report a case of a parturient with documented chronic Chagas' disease with cardiac manifestations presenting for labor management and complicated by the need for emergent hysterectomy after delivery. Chagas' disease is a common human hematogenous trypanosomiasis in Central and South America which is now, because of population migration, appearing in the USA. This disease predominantly affects the heart and the gastrointestinal system. This report discusses the parasite, the acute and chronic phases of Chagas' disease and highlights its medical implications, including maternal-fetal transfer of Trypanosoma cruzi.

Arming alpha 2-macroglobulin with ricin A chain forms a cytotoxic conjugate that inhibits protein synthesis and kills human fibroblasts.

A conjugate containing alpha 2-macroglobulin and highly purified ricin A chain was made using N-succinimidyl-3-(2-pyridyldithio)propionate. Radioimmunoassay indicated that it contained 1.2 mol A chain per mol alpha 2-macroglobulin. The conjugate inhibited polyuridylic-acid directed translation by rat liver ribosomes and protein synthesis in human fibroblasts. There was a 90 min lag period before the beginning of inhibition in fibroblasts, but complete inhibition could be achieved. By measuring protein synthesis as a function of protein concentration, it was demonstrated that 8.25 X 10(-9) M conjugate was required to inhibit 50% of protein synthesis in 6 h. To achieve the same level of inhibition, 165-times more (1.3 X 10(-6) M) unconjugated A chain was required, and 180-times less ricin (4.6 X 10(-11) M). Ricin was more than 28 000 times more inhibitory than A chain alone. The presence of alpha 2-macroglobulin did not increase the cytotoxicity of unconjugated A chain, and it even protected the cells to a slight extent. The inhibitory action of the conjugate was blocked by antibodies specific for alpha 2-macroglobulin or ricin, and it was not prevented by galactose or antibodies specific for ricin B chain. Electron microscopy of the conjugate indirectly labelled with ferritin demonstrated that it was internalized by receptor mediated endocytosis through coated pits. These data indicate that the A chain portion of the conjugate survives the conditions in the lysosomes to the extent that it retains its ability to inactivate cytoplasmic ribosomes.

An alternative approach to teaching statistics to dental students.

From a review of the literature, instruction in statistics appears to be common in dental schools but beset with problems. Based, in part, on several surveys of the statistics content of dental literature, there is some general agreement that dentists-in-training need to acquire a working knowledge of statistics. Content guidelines developed for health science statistics courses are available and are considered entirely appropriate for dental education. Several authors have suggested that computer-assisted instruction is ideally suited to minimize the problems encountered in teaching statistics to dental students. Computer-assisted instruction is expensive, however, and self-instruction using a programmed text was found, on the basis of preliminary evaluation, to be an effective and inexpensive alternative.