Melittin and a chemically modified trichotoxin form alamethicin-type multi-state pores

The bee venom constituent, melittin, is structurally and functionally related to alamethicin. By forming solvent-free planar bilayers of small area (approx. 100 microns 2) on the tip of fire-polished glass pipettes we could observe single melittin pores in these membranes. An increase in the applied voltage induced further non-integral conductance levels. This indicates that melittin forms multi-level pores similar to those formed by alamethicin. Trichotoxin A40, an antibiotic analogue of alamethicin, also induces a voltage-dependent bilayer conductivity, but no stable pore states are resolved. However, chemical modification of the C-terminal molecule part by introduction of a dansyl group leads to a steeper voltage-dependence and pore state stabilization. Comparing structure and activity of several natural and synthetic amphiphilic polypeptides, we conclude that a lipophilic, N-terminal alpha-helical part of adequate length (dipole moment) and a large enough hydrophilic, C-terminal region are sufficient prerequisites for voltage-dependent formation of multi-state pores.     

Movement characteristics and acrosomal status of rabbit spermatozoa recovered at the site and time of fertilization

Rabbit spermatozoa were recovered from the oviductal ampullae 11 h postcoitus by an oil microflush technique. Their movement was evaluated in the ampullar fluid, or in ampullar fluid diluted with in vitro fertilization medium, in slide preparations which were approximately 25 micron or 100 micron deep. The movement of these sperm was compared with the movement of ejaculated sperm in diluted semen. Movement parameters measured from videotapes recorded by a high-speed camera were coded according to treatment and entered into a microcomputer for statistical analysis. A total of 157 spermatozoa were recovered from the oviducts of 16 does: 152 were motile and 126 were free-swimming. Nearly all of the free-swimming sperm swam in trajectories whose average paths were circular. The flagellar beat pattern of the circular swimmers was asymmetric and nearly planar, and the sperm did not roll. Spermatozoa observed in 25-micron slide preparations produced smaller flagellar bends than sperm swimming in 100-micron preparations and tended to swim in larger circles which were oriented in the plane of the slide. Spermatozoa observed within the cumulus matrix moved in a slow, erratic, sinuous manner, but resumed rapid circling upon leaving the matrix. It was concluded that the ampullar sperm were hyperactivated, retaining this physiological condition as they entered the cumulus. The movement qualitatively resembled that of hyperactivated guinea pig and hamster spermatozoa because these species effectively swim in circles. In contrast, 80% of the ejaculated spermatozoa swam in linear trajectories, resulting from relatively symmetrical, flagellar beat patterns. The percentage of rolling spermatozoa and the rolling frequencies were less in the 25-micron than the 100-micron slide preparations. Thus, the movement parameters of both ampullar and ejaculated spermatozoa were affected by the geometry of their observation chambers. This influence should be taken into account when observing sperm motility in vitro. It could also be important in vivo, where changes in sperm movement in response to epithelial surfaces might provide an advantage for reaching the cumulus mass. Ninety-eight percent of the motile ampullar sperm were observed to have acrosomes, including all spermatozoa found within the cumulus matrix.     

Experimental design for estimating integrals by numerical quadrature, with applications to pharmacokinetic studies

Many experimental situations, including bioavailability studies, require the estimation of integrals by numerical quadrature applied to dependent variable observations with measurement error. A strategy is described for selecting values for the independent variable (e.g. time). The strategy minimizes the expectation of the square of the difference between the exact integral and the quadrature approximation. This approach was applied to simulated pharmacokinetic problems, including the estimation of bioavailability. Results indicate that the procedure is potentially useful in reducing the variance of resulting estimates and that it appears to be robust with respect to prior assumptions about model parameter values.     

Immune response genes in inbred rats. II. Segregation studies of the GT and GA genes and their linkage to the major histocompatibility locus

Genetic analysis of the high responder-non-(or low) responder differences between WF and ACI rats to the synthetic copolymers GT and GA established singleIr-genes for both antigens and dominance for high responder status.Ir-GT andIr-GA are linked to the major histocompatibility locus. It could be demonstrated that only T cells carrying the high responderIr-GT gene undergo in vitro blast transformation to GT. The advantages of the rat systems for further studies of the regulatory role ofIr-genes on the cellular level are discussed.Abbreviations cpm counts per minute - DHR delayed hypersensitivity reaction - GA random synthetic copolymer of L-glutamic acid⁵⁰, L-alanine⁵⁰, M.W. 45,000 - GT random synthetic copolymer of L-glutamic acid⁵⁰, L-tyrosine⁵⁰, M.W. 22,000 - Ir gene immune response gene - MLC mixed lymphocyte cultures - LDH lactic dehydrogenase - (T,G)-A-L branched chain synthetic polymer of poly-L (tyrosine, glutamic acid)-poly-D, L-alanine-poly-L-lysine Rat Strains ACI ACI/MaI - WF Wistar Furth - AUG August 28807/Cr     

Flow through a Collapsible Tube: Experimental Analysis and Mathematical Model

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.     

Secretory IgA in Urinary Tract Infections

Secretory IgA, measured by radial immunodiffusion, was compared in the urine of children with chronic and recurrent non-obstructive urinary tract infections with that in normal children. IgA, IgG, and IgM were also measured. Absent and low levels of IgA(s) were found in both groups; however, the mean levels of IgA(s) were significantly higher in the infected group compared with normals—3·3 to 0·78 mg./24 hours, respectively. Secretory IgA was found to be locally produced in the bladder. It is suggested that IgA(s) levels reflect an antibody response to infection.