Relic pleistocene permafrost, Western arctic, Canada.

Icy layers and interbedded frozen sediments along the Arctic Coastal Plain of northwestern Canada have been subjected to glacial deformation. Radio-carbon dates indicate that the deformation took place more than 40,000 years ago.

Regulation of insulin secretion by cAMP in rat islets of Langerhans permeabilised by high-voltage discharge.

Adenosine 3',5-cyclic monophosphate (cAMP) was shown to stimulate insulin secretion from electrically permeabilised islets of Langerhans incubated in Ca2+/EGTA buffers. cAMP-induced insulin secretion occurred in the presence of either sub-stimulatory (50 nM) or stimulatory (greater than 100 nM) concentrations of Ca2+. Similar effects on secretion were obtained in response to 8-bromo-cAMP (8-Br-cAMP) or the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine. Forskolin (0.2-20 microM) increased adenylate cyclase activity and enhanced insulin secretion from the permeabilised islets. These results suggest that, in electrically permeabilised islets, cAMP-induced insulin secretion is not dependent on changes in cytosolic Ca2+.

Catecholamine inhibition of Ca2+-induced insulin secretion from electrically permeabilised islets of Langerhans.

Noradrenaline (1-10 microM) inhibited Ca2+-induced insulin secretion from electrically permeabilised islets of Langerhans with an efficacy similar to that for inhibition of glucose-induced insulin secretion from intact islets. The inhibition of insulin secretion from permeabilised islets was blocked by the alpha 2-adrenoreceptor antagonist, yohimbine. Adenosine 3',5'-cyclic monophosphate (cAMP) did not relieve the noradrenaline inhibition of Ca2+-induced secretion from the permeabilised islets, although noradrenaline did not affect the secretory responses to cAMP at substimulatory (50 nM) concentrations of Ca2+. These results suggest that catecholamines do not inhibit insulin secretion solely by reducing B-cell adenylate cyclase activity, and imply that one site of action of noradrenaline is at a late stage in the secretory process.

The characteristics of beta-adrenergic binding sites on pancreatic islets of Langerhans.

The sympathetic nervous system is believed to play a part in the control of insulin release from the pancreatic islets of Langerhans. Stimulation of alpha-adrenoceptors is thought to inhibit the release of insulin whereas stimulation of beta-adrenoceptors enhances insulin release. The present experiments were conducted to establish the existence of beta-adrenergic receptors on guinea-pig and rat islet cells and to quantify them using the selective beta-adrenergic ligands [3H]dihydroalprenolol (DHA) and [125I]cyanoiodopindolol (CYP). Guinea-pig islets had 62 fmol beta-adrenoceptors/mg protein using [3H]DHA, corresponding to 43,700 binding sites/cell and 25 fmol beta-adrenoceptors/mg protein using [125I]CYP, corresponding to 17,400 sites/cell. Rat islet cells were found to have 4.6 fmol beta-adrenoceptors/mg protein using [125I]CYP, corresponding to 7200 sites/cell. Adenylate cyclase activation exhibited a positive dose-response relationship when exposed to the beta-adrenoceptor agonist isoprenaline, with a maximum response (190 +/- 21% above basal) at 10 mumol isoprenaline/l. This response was abolished with 1 mumol/l of the beta-adrenergic antagonist l-alprenolol. Insulin secretion in the presence of 10 mmol glucose/l, but in the absence of the alpha-adrenoceptor blocker phentolamine, was not affected by 10 mumol isoprenaline/l. However, perifusion experiments showed that secretion of insulin from isolated rat islets in the presence of 10 mmol glucose/l was significantly increased (332%) by 10 mumol isoprenaline/l in the presence of 10 mumol phentolamine/l. These results suggest that binding of selective radiolabelled ligands occurs to beta-adrenergic receptors on the B cell surface of the islets of Langerhans, and that these receptors are functionally coupled to insulin secretion through modulation of adenylate cyclase activity.

The determination of alpha-adrenergic receptor concentration on rat pancreatic islet cells.

The selective alpha 2 adrenergic antagonist yohimbine has been shown to prevent the noradrenaline induced inhibition of insulin secretion from isolated rat islets of Langerhans. Binding studies utilizing [3H]yohimbine showed specific binding to dispersed rat islet cells with a Kd of 2.9 nM and receptor concentration of 645 fmols/mg protein. The use of chloroquine to inhibit receptor recycling did not affect binding of the ligand. Binding studies and secretion data are consistent with the suggestion that adrenergic receptors of the alpha 2 sub-type may play a dominant role in the regulation of insulin secretion.

Polymerase chain reaction-mediated gene synthesis: synthesis of a gene coding for isozyme c of horseradish peroxidase.

The synthesis of a gene coding for horseradish peroxidase (HRP, isozyme c; EC 1.11.1.7) is described using a polymerase chain reaction (PCR)-mediated gene synthesis approach developed in our laboratory. In this approach, all the oligonucleotides making up the gene are ligated in a single step by using the two outer oligonucleotides as PCR primers and the crude ligation mixture as the target. The PCR facilitates synthesis and purification of the gene simultaneously. The gene for HRP was synthesized by ligating all 40 oligonucleotides in a single step followed by PCR amplification. The gene was also synthesized from its fragments by using an overlap extension method similar to the procedure as described [Horton, R. M., Hunt, H. D., Ho, S. N., Pullen, J. K. & Pease, L. R. (1989) Gene 77, 61-68]. A method for combining different DNA fragments, in-frame, by using the PCR was also developed and used to synthesize the HRP gene from its gene fragments. This method is applicable to the synthesis of even larger genes and to combine any DNA fragments in-frame. After the synthesis, preliminary characterization of the HRP gene was also carried out by the PCR to confirm the arrangement of oligonucleotides in the gene. This was done by carrying out the PCR with several sets of primers along the gene and comparing the product sizes with the expected sizes. The gene and the fragments generated by PCR were cloned in Escherichia coli and the sequence was confirmed by manual and automated DNA sequencing.

Effects of calcium on light-activated GTP-binding proteins in squid photoreceptor membranes.

1. At least two distinct G-proteins are activated by light in squid photoreceptor membranes, a 45,000 mol. wt cholera toxin substrate and a 40,000 mol. wt pertussis toxin substrate. 2. The light-stimulated GTPase activity is partially inhibited by pretreatment with either toxin and abolished by treatment with both toxins. 3. At 24 degrees C, a free calcium ion concentration of 1 microM inhibits GTPase activity of both toxin substrates and ADP ribosylation by pertussis toxin. 4. This calcium sensitivity of squid G-proteins may be important in interpretation of experimental results on the phosphoinositide or other signalling pathways in squid visual transduction.

Fluctuations of climatic conditions, elemental cycling and forest growth at the watershed scale.

The relationships between fluctuations in climatic conditions, forest productivity and elemental cycling were studied from 1994 to 1997 in a headwater catchment of the southern Laurentians dominated by sugar maple (Acer saccharum Marsh.) growing on podzolic soils. Annual budgets show that H+, K, and NO3 were retained in the watershed while Ca, Mg and Na were lost. The magnitude of the net annual budget for Ca, Mg and Na was correlated to annual variations in precipitation with the absolute budget value decreasing during dry years. Stemwood (r2 = 0.85) and total tree biomass production (r2 = 0.99) were correlated with mean annual temperature but fine roots and leaf litter were not. During the growing season, the pH of the organic horizons (FH) decreased as the volumetric water content of soil decreased. A positive association was also found between air temperature and H2O-soluble (r2 = 0.88) and PO4-extractable (r2 = 0.99) SO4 in the upper B horizon. On a multiyear scale, we suspect that the decrease in the storage of inorganic SO4 in the soil results from the cumulative effects of annual variations in climatic conditions superimposed on the long-term decrease in SO4 deposition from the atmosphere. These soil changes were reflected by a decline in SO4, Ca and Mg concentrations in the stream. The generalisation of the observed short-term patterns to longer time scales must be approached with caution. Yet, our results indicate that the associations between climatic variations and the biogeochemistry of the ecosystem occur at different spatial and temporal scales and integrate a broad range of chemical components and ecosystem compartments. This reflects the inherent complexity of natural systems and offers a vast palette of indicators of the response of terrestrial ecosystems to variations in the intensity of environmental factors such as climatic conditions.