David Jesús Palma López

Accumulated Bending Energy Elicits Neutral Sphingomyelinase Activity in Human Red Blood Cells

We propose that accumulated membrane bending energy elicits a neutral sphingomyelinase (SMase) activity in human erythrocytes. Membrane bending was achieved by osmotic or chemical processes, and SMase activity was assessed by quantitative thin-layer chromatography, high-performance liquid chromatography, and electrospray ionization-mass spectrometry. The activity induced by hypotonic stress in erythrocyte membranes had the pH dependence, ion dependence, and inhibitor sensitivity of mammalian neutral SMases. The activity caused a decrease in SM contents, with a minimum at 6 min after onset of the hypotonic conditions, and then the SM contents were recovered. We also elicited SMase activity by adding lysophosphatidylcholine externally or by generating it with phospholipase A(2). The same effect was observed upon addition of chlorpromazine or sodium deoxycholate at concentrations below the critical micellar concentration, and even under hypertonic conditions. A unifying factor of the various agents that elicit this SMase activity is the accumulated membrane bending energy. Both hypo-and hypertonic conditions impose an increased curvature, whereas the addition of surfactants or phospholipase A(2) activation increases the outer monolayer area, thus leading to an increased bending energy. The fact that this latent SMase activity is tightly coupled to the membrane bending properties suggests that it may be related to the general phenomenon of stress-induced ceramide synthesis and apoptosis.

Chemical Characteristics Of Several Vermicomposts In México

Wastes were collected (cocoa husk, sugarcane bagasse, sugarcane filter cake and bovine manure) in Tabasco State, México. These were vermicomposted, mixed and pretreated for temperature stabilization. The wastes were then vermicomposted with earthworms of the specie Eisenia andrei. Data were collected 60 days after the earthworms were inoculated. The vermicompost obtained was also chemically characterized. The objectives of this study were to evaluate the survival of earthworms (Sv) in several wastes and to assess the capacity of the earthworms to produce vermicompost (Vp). Waste with high C/N ratio had lower Vp, although the Sv was not affected. The C/N ratio was closely associated with the quality of organic matter (OM); when wastes had high content of nitrogen compounds, the C/N ratio decreased. The integration of cocoa husk in the treatment improved Sv, while the mixture of filter cake and bovine manure (1:1) was the optimum treatment for Vp. Important changes concerning the chemical characteristics of the vermicompost due to the influence of earthworms were not observed.