Specific binding and pharmacological interactions of apamin,the neurotoxin from bee venom,with guinea pig colon

This paper describes the interaction of apamin, the bee venom neurotoxin, with its receptor in the guinea pig colon. The pharmacological activity of the toxin was assayed by measuring its contracting effect on guinea pig colon preparations that had been previously relaxed by neurotensin. The IC₅₀ value of apamin in this $\text{in vitro}$ bioassay is 7 nM. These pharmacological data are compared to the binding properties of apamin to smooth muscle membranes prepared from guinea pig colon. The highly radiolabeled monoiododerivative of apamin binds to its colon receptor with a dissociation constant $\text{K}{}_{\mathrm{<mtext>d</mtext>}}{}^1\text{= 36}\text{pM}$. The maximal binding capacity of colonic membranes is 30^dfmol/mg of protein. The dissociation constant of the unmodified toxin is 23 pM. The difference between the toxin concentrations that produce half-maximal effects in the binding and pharmacological studies arises from the different experimental conditions used for the two assays.     

The Role of Estrogens as a Risk Factor for Stroke in Postmenopausal Women

The estrogen component in oral contraceptives is generally thought to increase the risk of stroke in users as compared with controls. If this were true, an increased risk for stroke also should be seen among postmenopausal women using estrogens as compared with nonusers. To test this hypothesis, the charts of 198 postmenopausal patients who had had strokes were compared with those of 396 controls for estrogen use and for the associated risk factors of diabetes, hypertension and coronary artery disease. The difference between estrogen use in the study population versus controls proved not significant, and the use of estrogens did not significantly influence the distribution of the above risk factors. We concluded that the use of estrogens in physiological replacement doses does not increase the risk of stroke in postmenopausal women.     

Thermophilic mycoflora of cigarettes and cured tobacco leaves

Nine species of thermophilic fungi were obtained from retailed packets of imported and locally manufactured brands of cigarettes and from cured tobacco leaves. They include known human pathogens such asThermoascus aurantiacus Miehesensu Apinis,Mucor pusillus Lindt andMucor miehei Cooney and Emerson. Chaetomium thermophile La Touche,Humicola insolens Cooney and Emerson,Thermoascus crustaeus (Apinis and Chesters) Stolk andMucor miehei have not been previously reported on tobacco products.Fewer species were obtained from foreign cigarettes than from locally manufactured brands. A mean moisture content of 19% was recorded for imported cigarettes and 37% for Nigerian brands. The potential health hazards posed to man by the unrestricted use of tobacco products are discussed.     

Comparison of pyloric ligation and pyloric cuff techniques for collecting gastric secretion in the rat.

A comparison was made between two methods for collecting gastric secretion in the rat. The two included a pyloric ligation technique and a snare-type pyloric cuff which was surgically implanted 2 weeks before the collection was initiated. It was hypothesized that the surgical trauma associated with pyloric ligation would inhibit gastric secretion and thus yield smaller gastric samples with this procedure as compared to the cuff technique. No differences in volume of gastric secretion or total acid output were observed between the two methods.     

Rapid physiological assays for nutrient demand by the plankton. I. Nitrogen

Three assays for nitrogen demand were compared on samples ofnatural plankton and on green and blue-green algal species inculture. The most reliable guide was selective luxury uptakeof nitrogen by the plankton after enrichment with a 10-to-1(wt/wt) mixture of inorganic N and P. Ammonium transport capacity,measured either directly (cultures) or by V_max for uptake ofthe NH₄⁺ analogue methylammonium (lakewaters), was generallyhigh in lakewaters with low dissolved inorganic N-to-P ratiosand in N-deficient cultures of green algae. By contrast, transportcapacity was much reduced in both natural and cultured populationsof heterocystous blue-green algae growing under conditions oflow combined inorganic nitrogen. Ammonium enhancement assays(heterotrophic CO₂, fixation after NH₄⁺ enrichment) were conductedat monthly intervals on eutrophic Lake Rotorua. There was astrong, negative correlation between this indicator of N deficiencyand dissolved inorganic N-to-P ratios below a threshold of 6:1.Ammonium enhancement was not, however, a reliable indicatorof combined inorganic N-demand by populations of heterocystousblue-green algae. All three assays provided strong evidenceof a persistent shortage of nitrogen relative to phosphorusfor algal production in Lake Rotorua.     

The Yale Affiliated Hospital Program in Internal Medicine

In July, 1975, the Departments of Internal Medicine at the Yale University School of Medicine and eight community hospitals in southern and western Connecticut formed the Yale Affiliated Hospital Program (YAHP) in Internal Medicine. The YAHP provides a planned and focused program of continuing education for medical staff and housestaff at the affiliated hospitals. Six formats for the over 1,000 rounds, lectures, and conferences given annually are used. The members of the YAHP also cooperate in housestaff and faculty recruiting, evaluation of quality of care and evaluation of the process of continuing medical education itself. This report summarizes the organization, goals and future plans of the YAHP.     

Flexibility of the pyrrolidine ring in proline peptides

A survey of over 50 crystal structures indicates that both imino acid and peptide derivatives of proline populate ring conformers consistent with the torsional potentials about single bonds. In both cases, lower barriers for rotation about C? N bonds relative to those about C? C bonds favor smaller values for dihedral angles about the former bonds. In peptides a minimum in the torsional potential about C? N bonds occurs at zero dihedral angle, further favoring small angles. The pyrrolidine-ring dihedral angles of the proline compounds in the solid state obey a cyclopentane-type pseudorotation function. Thus the puckering of the five-membered ring can be quantitatively described by two parameters. Consistent with small dihedral angles about C? N bonds, C^β and/or C^γ are puckered out of the mean plane of the ring in nearly all of the nonstrained compounds. Utilizing the consistent force-field method of Lifson and coworkers [see A. Warshel, M. Levitt, and S. Lifson (1970) J. Mol. Spectrosc. 33 , 84] the intramolecular energy of five proline peptides was minimized with respect to all internal coordinates. In addition, the energy surface near minima was explored by constraining a particular dihedral angle and reminimizing the energy with respect to all remaining variables. In linear peptides two types of pyrrolidine-ring conformers have identical predicted energies. In the cyclic dipeptide cyclo (Pro-Gly) one of the ring conformers is favored by about 3 kcal/mol, while the cyclic tripeptide cyclo(Pro-Gly-Gly) favors the other conformer by a comparable margin. In agreement with observations in the solid state and in solution, C^β and/or C^γ are puckered in the predicted conformers. A correlation between proline Φ and the details of the puckered conformation was predicted and found to match precisely conformers observed in crystals. For the diamides N-acetyl-L -proline-N′-methyl-amide and N-acetyl-L -proline-N′,N′-dimethylamide (AcProMe₂A) 30% and 60% cis acetyl peptide bonds were predicted in good agreement with observations in nonpolar solvents for the respective compounds. The conformational distributions with respect to proline Ψ are also in accord with experimental observations. For AcProMe₂A, a model for a -Pro-Pro-sequence in a peptide chain, this study is the first to predict stable conformers for proline Ψ either ca. ?50° or 140° for both cis and trans peptides.     

Quinine-induced agranulocytosis: toxic effect of quinine bisulphate on bone marrow cultures in vitro.

In a case of quinine-induced agranulocytosis marrow culture studies confirmed the inhibitory effect on the patient''s cells of equivalent therapeutic plasma concentrations of quinine. Similar concentrations had no effect on normal marrow cells. Quinidine, the stereoisomer of quinine, had no effect on either cells from the patient or normal cells. The results encourage the use of in-vitro bone marrow cultures for identifying drugs responsible for agranulocytosis.     

Structural changes of isolated hepatocytes during treatment with digitonin

The structural changes accompanying digitonin-induced release of enzymes and metabolites from isolated hepatocytes have been studied by scanning and transmission electron microscopy. In the initial phase, characterized by total release of the cytosolic marker enzyme, lactate dehydrogenase, the plasma membrane was immediately damaged, rapidly followed by extensive damage to the endoplasmic reticulum. The shape of the cell, however, was maintained, and the mitochondria and nucleus remained tightly held together by the cytoskeleton. Mitochondria remained intact initially, whereas the cytosol became less electron dense and the nuclear chromatin was more dispersed. An intermediate phase was characterized by total release of adenylate kinase and most of the glucose-6-phosphatase, marker enzymes for the mitochondrial intermembrane space and the endoplasmic reticulum, respectively. The outer mitochondrial membrane was ruptured, but mitochondria maintained their normal matrix electron density. In the final phase, characterized by the beginning of citrate synthase release from the mitochondrial matrix space, the mitochondria became swollen, and only the nucleus, inner and outer mitochondrial membranes, and the cytoskeleton could be clearly distinguished. Although the plasma membrane could not be readily discerned in electron micrographs after the initial phase, the plasma membrane marker enzyme 5′-nucleotidase remained associated with digitonin-treated hepatocytes. Acetyl-CoA carboxylase was released much more slowly than lactate dehydrogenase, indicating some severe restriction on its release. The release of acetyl-CoA carboxylase closely paralleled the release of glucose-6-phosphatase. The controlled exposure of hepatocytes to digitonin, therefore, leads to the sequential release of soluble, compartmentalized cellular components and some membrane-bound components, but the mitochondrial membrane, cytoskeleton and the nucleoskeleton survive even long-term digitonin treatment.