Regulation of pancreatic exocrine secretion in vitro: the action of secretagogues

Pancreatic acinar cells possess two functionally distinct mechanisms by which secretagogues can increase enzyme secretion. One mechanism is mediated by mobilization of cellular calcium and can be activated by any one of four different classes of receptors. The other mechanism is mediated by cyclic AMP and can be activated by either of two different classes of receptors. In addition to stimulating enzyme secretion, a secretagogue can cause potentiation of secretion, desensitization to the subsequent stimulation caused by the same or other secretagogues as well as residual stimulation of enzyme secretion. Although each class of secretagogue receptors can cause the same final effect, stimulation of enzyme secretion, the existence of multiple classes of receptors and the different mechanisms of action endow the acinar cell with a wide range of patterns of response depending on which of the several classes of receptors are activated.     

The absorption of protons with alpha-methyl glucoside and alpha-thioethyl glucoside by the yeast N.C.Y.C. 240. Evidence against the phosphorylation hypothesis.

1. When yeast N.C.Y.C. 240 was grown with maltose in a complex medium based on yeast extract and peptone, washed cell preparations fermented alpha-methyl glucoside much more slowly than maltose. 2. The yeast absorbed alpha-methyl[14C]glucoside from a 10mM solution in the presence of antimycin and iodoacetamide, producing [14C]glucose, which accumulated outside the cells. The yeast itself contained hexose phosphates, trehalose, alpha-methyl glucoside and other products labelled with 14C, but no alpha-methyl glucoside phosphate. 3. About 1 equiv. of protons was absorbed with each equivalent of alpha-methylglucoside, and 1 equiv. of K+ ions left the yeast. 4. alpha-Thioethyl glucoside was also absorbed along with protons. Studies by g.l.c. showed that the yeast concentrated the compound without metabolizing it. 5. The presence of trehalose, sucrose, maltose, L-sorbose, glucose or alpha-phenyl glucoside in each case immediately stimulated proton uptake, whereas fructose, 3-O-methylglucose and 2-deoxyglucose failed to do so. 6. The observations support the conclusion that alpha-thioethyl glucoside, alpha-methyl glucoside and maltose are substrates of one or more proton symports, whereas they seem inconsistent with the notion that the absorption of alpha-methyl glucoside involves the phosphorylation of the carbohydrate [Van Stevenick (1970) Biochim. Biophys. Acta 203, 376-384].     

Defluorination of fluoroacetate in the rat

Rats given 5 ppm F as FAc (equivalent to 26 ppm of NaFac) in the drinking water for approximately four months deposited as much fluoride in the skeletal system as did rats receiving 5 ppm F as NaF in the water. Little evidence could be found for the presence of organically bound fluoride in bone after ingesting FAc, though an appreciable proportion of skeletal fluoride deposited when NaF was ingested was shown not to respond to the fluoride ion electrode. The daily urinary excretion of total fluoride after FAc was somewhat greater than after NaF; about two thirds of this fluoride responded to the electrode, whereas more than 90 percent of the total fluoride after NaF was ionic in nature. The data are interpreted as showing that the rat is capable of splitting the C-F bond in FAc and/or in its fluoride-containing metabolites, with subsequent skeletal storage and renal excretion of the released fluoride ion. The chronic administration of this low level of FAc caused an early but temporary retardation of growth. The Krebs cycle was interfered with, as evidenced by increased concentrations of citrate in the kidney and urine. At termination of the experiment, histological examination of the testes showed that the FAc had induced severe damage characterized by massive disorganization of the tubules, nearly total loss of functional cells, absence of sperm, and damage to the Sertoli cells.     

Identification and restriction endonuclease mapping of the threonine operon regulatory region.

A DNA fragment carrying the thrP region of Escherichia coli has been identified and characterized. Starting from a secondary site lysogen of bacteriophage λ, where the position of the prophage is either within thrP or between thrP and thrP structural genes (Gardner et al., 1974; Gardner &; Smith, 1975) it has been possible to isolate transducing phages which carry bacterial DNA from either side of the prophage. By Int-Xis mediated site-specific recombination we have generated recombinant transducing phages which carry an intact thrP region. A phage carrying a regulatory mutation, which maps in the thrP region, has also been constructed.Mapping with several restriction endonucleases has allowed us to construct a map of the cleavage sites of the thrP region. A 1700 base-pair HaeIII fragment carrying the secondary attachment site (attΔOΔ′) was isolated and its position was localized within a 180 base-pair TaqI-HhaI restriction fragment. The location of attΔOΔ′ in the HaeIII fragment suggests that the entire thrP region is carried by this fragment.     

In vitro cytokinin binding to a particulate cell fraction from protonemata of Funaria hygrometrica

Cytokinin-induced bud formation in moss protonemata is specific for cytokinin bases, their ribosides being relatively inactive. Binding of [³H]benzyladenine (BA) to a 13,000–80,000 x g subcellular fraction from extracts of Funaria hygrometrica (L.) Sibth. was measured by a centrifugation assay. Increasing concentrations of non-radioactive BA decreased the binding proportionally to the logarithm of the BA concentration between 3×10^-8 and 10^-4M. [³H]Zeatin also bound to these fractions, although the extent of binding was not as great as with [³H]BA. Biologically active cytokinins, including BA, zeatin, 6-(3-methyl-2-enylamino)purine (IPA) and kinetin, competed for the binding of [³H]BA, whereas the ribosides of BA, zeatin and IPA competed poorly. Other biologically inactive compounds, such as adenine and 9-methyl-BA, were also ineffective as competitors. The ability to bind BA by the 13,000–80,000 x g fraction was greatly reduced by treatment with 1% Triton X-100, and heat treatment eliminated more than one-half of the binding activity. Competitive binding appeared to be pH-dependent, with maximal activity between pH 6.0 and 6.5. After fractionation by differential centrifugation, the ability to bind cytokinins was not correlated with the RNA content of the fraction and thus probably did not represent binding to ribosomes which has been reported in other plant tissues. Cytokinins also exhibited competitive binding to non-biological materials, e.g., talc. The detailed characteristics of the binding of BA to talc were different from those to the biological fractions. However, the problem remains, in all studies of cytokinin binding, to distinguish between binding that is biologically meaningful, and biological (biologically) non-meaningful physical adsorption.Abbreviations BA N⁶-benzyladenine - IPA 6-(3-methyl-2-enylamino)purine - 9-MeBA N⁶-benzyl-9-methyladenine     

Paget's disease of bone in 14 British towns.

The radiological prevalence of Paget''s disease was studied in 14 towns. Routine radiographs showed that the disease was present in 5.4% of people aged 55 years and over. The disease was more prevalent in men than in women at all ages, and the prevalence increased with age. The three Lancashire towns studied (Preston, Bolton, and Blackburn) had higher rates than elsewhere. This probably reflects a real geographical variation in the prevalence of Paget''s disease in England and Wales.     

Action of cholera toxin on dispersed acini from rat pancreas. Post-receptor modulation involving cyclic AMP and calcium

In dispersed acini from rat pancreas, cholera toxin caused a significant increase in cellular cyclic AMP but little or no change in amylase secretion. The presence of a secretagogue that causes mobilization of cellular calcium (e.g., cholecystokinin, carbamylcholine, bombesin or ionophore A23187) caused a substantial increase in the effect of cholera toxin on enzyme secretion. Cholera toxin did not alter calcium transport or the changes in calcium transport caused by other secretagogues, and secretagogues that mobilize cellular calcium did not alter cellular cyclic AMP or the increase in cyclic AMP caused by cholera toxin. These results indicate that in dispersed acini from rat pancreas there is post-receptor modulation of the action of cholera toxin by secretagogues that mobilize cellular calcium and that this modulation is a major determinant of the effect of the toxin on enzyme secretion.     

Fixing coccidian oocysts is not an adequate solution to the problem of preserving protozoan type material

Fresh (36 days old) sporulated oocysts of Eimeria nieschulzi were divided into 7 groups. Control oocysts were maintained at 23 C in 2% aqueous (w/v) K2Cr2O7. The 6 experimental groups were mixed with either Bouin's solution, 10% aqueous (v/v) buffered formalin, Karnovsky's solution, glutaraldehyde, paraformaldehyde, or 70% aqueous (v/v) ethanol (EtOH). After 115 days, oocysts from all 7 groups were examined under oil immersion to determine the effect of fixation on their structural integrity. The parameters examined were lengths and widths of oocysts and sporocysts, percent sporulation (%S), and percent crenation (%C) of oocysts and sporocysts. The highest destruction (%S and %C) occurred in oocysts exposed to glutaraldehyde and Karnovsky's fixatives where 100% of both oocysts and sporocysts crenated and only 8% and 48%, respectively, remained sporulated. Of the oocysts in paraformaldehyde, 93% remained sporulated, but 95%of these oocysts and 100% of the sporocyst crenated. In Bouin's solution, 75% of the oocysts were intact structurally, but of these, only 60% were still sporulated with 70% of their sporocysts crenated. Oocysts preserved in 70% EtOH were 80% intact and 70% remained sporulated, but nearly 60% of their sporocysts collapsed even though the oocyst walls were intact. Oocysts preserved in 10% buffered formalin maintained structural integrity but had lower numbers of sporulated oocysts (84%) and greater numbers of crenated oocysts (18%) than control oocysts maintained in the dichromate solution (95% and 0%, respectively).     

Plankton ecology in an ice-covered bay of Lake Michigan: utilization of a winter phytoplankton bloom by reproducing copepods

Plankton ecology was examined during the 1986 winter in Grand Traverse Bay, a 190 m deep, fjordlike bay on Lake Michigan. Before ice cover, algal concentration was low and uniformly distributed with depth, as it is in open Lake Michigan. During ice cover (February and March), a bloom of a typical winter-spring phytoplankton community developed in the upper 40 m, resulting in a 4 to 7-fold increase in feeding rate of adult Diaptomus spp. High algal concentration and zooplankton feeding persisted after ice melt (April). During and after ice cover, lipid concentrations of Diaptomus dropped rapidly from 34% of dry weight to 17 % because of egg production. High incident photosynthetically active radiation (PAR), high (45–50%) PAR transmittance of the ice due to little snow on the ice, and water column stability were probably responsible for the bloom. High ice transparency may be a common feature of large lakes and bays, where strong winds blow snow cover off the ice, or at low latitudes where snowmelt due to occasional rains and warm temperature is common. Winter reproducing calanoid copepods use these blooms to increase their reproductive output.