Coupling biological detection to liquid chromatography: a new tool in drug discovery.

Procedures to characterize drugs that can be obtained from plant extracts or combinatorial chemistry are tedious, and they consume considerable resources (e.g., animals) and time. Thus, we have looked for a way to streamline this process. We describe here a novel system for the pre-characterization of drugs based on liquid chromatography coupled to biological detection using perifused or perfused organs. This novel system allows the on-line detection of pharmacologically active substances in hydrosoluble mixtures from vegetal extracts or combinatorial chemistry libraries. Depending on the volume of drug solution and concentration of the samples, the procedure can work through either medium pressure liquid chromatography or HPLC, and it enables the fingerprints of drugs to be assessed based on their contractile activity on combinations of different isolated tissues. As an example, we show how the system can identify active fractions from an extract of Stevia rebaudiana Bertoni, an activity that was later associated with rebaudioside N. Coupling liquid chromatography to biological detection offers a rapid way to focus attention on active products in complex samples, mostly from hydrosoluble species, helping to considerably reduce the time and cost of the pre-characterization of drugs.

[Exocytosis as the mechanism for neural communication. A view from chromaffin cells]. / La exocitosis como mecanismo de comunicación neuronal. Una visión desde la célula cromafín.

Exocytosis constitutes the main cellular mechanism for secreting neurotransmitters. It entails the fusion of a secretory vesicle with plasma membrane, thus promoting the release of its soluble content. Among the cell models that have provided insight into molecular machinery underlying the succesive steps of exocytosis, adrenal chromaffin cells have taken a prominent place. Exocytosis gave support to the classical quantal theory, which maintains that neurotransmitters are released as discrete packages from the nerve terminals towards the postsynaptic cell. We present here a brief review of the estate of our knowlegments about the secretory vesicle traffic towards the cell membrane and how exocytosis takes place through the so called SNARE hypothesis. We also review the novel mechanisms implicated in the regulation of the late steps of exocytosis as well as their possible role as target for drug therapy