Late Glacial and Holocene environmental and climatic changes from a limnological transect through Colombia, northern South America

We present a synthesis of the palaeolimnological and palaeoclimatic reconstructions of four sites in Colombia. The record from Lake El Caimito, the westernmost site on the Pacific Coast, dates from the Late Holocene and shows lacustrine sedimentation frequently interrupted by fluvial pulses. These pulses probably reflect periods of increased precipitation related to La Niña phases. East of El Caimito site is the Patía swamp, situated between the Western and Central Andean Cordilleras. The Patía records the dynamics of forest expansion/reduction and changes in water levels. Although the climatic signal of the Patia core is difficult to reconstruct, there is a clear increase in humidity in the Mid-Holocene. The Fúquene Lake record, on the Eastern Andean Cordillera, records dry and cold conditions during the Late Pleistocene, very humid conditions for the early Mid-Holocene, and dry conditions during the mid-Late Holocene. Las Margaritas site, on the eastern savannas, records dry conditions during the Early Holocene and overall humid conditions for the Mid- and Late Holocene. Climate conditions from the Fuquene and Las Margaritas sites seem to reflect the Holocene movements of the Intertropical Convergence Zone (ITCZ); the latter site being more affected by humidity coming from the Amazon region.     

Fish population structuring in the North Sea: understanding processes and mechanisms from studies of the movements of adults

Few fish species form single, panmictic populations throughout their geographic range, most form subpopulations or 'stocks' with differing levels of interconnectivity. Different patterns of interconnectivity between subpopulations will give rise to different responses to exploitation and management, but they will also have different capacities to generate the genetic and phenotypic differences often used to discriminate between stocks. Consequently, knowledge of ontogenetic and seasonal patterns in the distribution, movement and behaviour of individuals is crucial to identifying population substructure. This paper considers the evidence gathered about movements and behaviour of adult fishes from mark-recapture and electronic tagging studies for a number of fish species in the North Sea and elsewhere in U.K. waters in an attempt to understand population structure and the processes that may give rise to it.     

Calcium regulates inositol 1,3,4,5-tetrakisphosphate production in lysed thymocytes and in intact cells stimulated with concanavalin A.

Lysed mouse thymocytes release [3H]inositol 1,4,5 trisphosphate from [3H]inositol-labelled phosphatidyl inositol 4,5-bisphosphate in response to GTP gamma S, and rapidly phosphorylate [3H]inositol 1,4,5-trisphosphate to [3H]inositol 1,3,4,5-tetrakisphosphate. The rate of phosphorylation is increased approximately 7-fold when the free [Ca2+] in the lysate is increased from 0.1 to 1 microM, the range in which the cytosolic free [Ca2+] increases in intact thymocytes in response to the mitogen concanavalin A. Stimulation of the intact cells with concanavalin A also results in a rapid and sustained increase in the amount of inositol 1,3,4,5-tetrakisphosphate, and a much smaller transient increase in 1,4,5-trisphosphate. Lowering [Ca2+] in the medium from 0.4 mM to 0.1 microM before addition of concanavalin A reduces accumulation of inositol 1,3,4,5-tetrakisphosphate by at least 3-fold whereas the increase in inositol 1,4,5-trisphosphate is sustained rather than transient. The data imply that in normal medium the activity of the inositol 1,4,5-trisphosphate kinase increases substantially in response to the rise in cytosolic free [Ca2+] generated by concanavalin A, accounting for both the transient accumulation of inositol 1,4,5-trisphosphate and the sustained high levels of inositol 1,3,4,5-tetrakisphosphate. Inositol 1,3,4,5-tetrakisphosphate is a strong candidate for the second messenger for Ca2+ entry across the plasma membrane. This would imply that the inositol polyphosphates regulate both Ca2+ entry and intracellular Ca2+ release, with feedback control of the inositol polyphosphate levels by Ca2+.     

Early axonal contacts during development of an identified dendrite in the brain of the zebrafish

We have identified the initial synaptic contacts made onto the Mauthner (M) cell, an identified neuron that arises during early development of the zebrafish hindbrain. The contacts are made by a small bundle of pioneering trigeminal sensory axons onto the M cell soma before it forms dendrites. The sensory bundle is then partially enveloped by the M cell. The lateral dendrite appears at about the site of the contact, and eventually the trigeminal inputs are shifted to its trunk. As the dendrite elongates, other sensory contacts are made on its distal regions, sequentially from the acoustico-vestibular nerve and the lateral line nerves. To learn whether the earliest inputs induce the initial outgrowth of the M cell dendrite, we ablated the trigeminal neurons by laser irradiation before they contacted the M cell. Morphogenesis of the M cell, including its dendrite, appeared normal.     

Design and properties of a fluorescent indicator of intracellular free Na+ concentration.

We have recently described a cryptand structure, FCryp-1, with appropriate properties for an indicator of intracellular free Na+ concentration using the 19F-n.m.r. chemical shift of the incorporated 5FBAPTA [1,2-bis-(2-amino-5-fluorophenoxy)ethane-NNN'N'-tetra-acetic acid] reporter group to measure the free cytosolic Na+ concentration [( Na+]i) [Smith, Morris, Hesketh and Metcalfe (1986) Biochim. Biophys. Acta 889, 82-83]. FCryp-1 carries four carboxylate groups to confer aqueous solubility and the indicator is membrane-permeant when the carboxyls are esterified with acetoxymethyl ester groups. Here we describe the synthesis of FCryp-2 to provide a fluorescent indicator of [Na+]i. FCryp-2 retains the parent tribenzo (2:2:1) cryptand structure of FCryp-1, in which the benzenoid ring at C-21 in FCryp-1 is replaced by an indole derivative which acts as the fluorophor in FCryp-2. With excitation at 340 nm, FCryp-2 gives an emission maximum at 460 nm in the absence of Na+ which shifts to 395 nm when FCryp-2 is saturated with Na+, with an isosbestic point at 455 nm. The apparent dissociation constant of FCryp-2 in a buffer solution of 100 mM-KCl/20 mM-KH2PO4/K2HPO4, pH 7.0, at 37 degrees C is 6.0 mM and the free Na+ concentration can be measured either from the calibrated fluorescence intensity at 395 nm, which increases 25-fold when Na+ is bound to FCryp-2, or from the ratio of fluorescence intensities at 395 nm and 455 nm. The measurement of free [Na+] by either method is unaffected by K+, Ca2+ or Mg2+ in the normal intracellular concentration ranges. Free [Na+] measurements by the ratio method are unaffected by pH from 6.6 to 7.6.     

Phosphoinositide metabolism and the calcium response to concanavalin A in S49 T-lymphoma cells. A comparison with thymocytes.

Comparisons were made between transformed S49 T-lymphoma cells and normal murine thymocytes in their polyphosphoinositides, inositol polyphosphates and cytosolic free calcium concentrations ([Ca2+]i), and the effects of the T-cell mitogen concanavalin A (Con A) on these properties. 1. The ratios of the polyphosphoinositides to phosphatidylinositol in both exponential-phase S49 cells and mitogen-stimulated thymocytes (G1 phase) were greater than in quiescent (G0-phase) thymocytes. 2. In response to Con A, the amount of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) in S49 cells decreased slightly (17% in 30 min), and this was sufficient to account for the small amounts of inositol phosphates that accumulated. In contrast, it has been shown previously that Con A stimulates a rapid resynthesis of PtdInsP2 in thymocytes and the amounts of inositol phosphates released rapidly exceed the steady-state amount of the PtdInsP2 precursor [Taylor, Metcalfe, Hesketh, Smith & Moore (1984) Nature (London) 312, 462-465]. 3. The [Ca2+]i did not differ significantly in S49 cells and thymocytes before the addition of Con A, and the increases in [Ca2+]i in response to Con A were similar in both types of cell. 4. The [Ca2+]i increase in response to Con A was inhibited by similar concentrations of intracellular cyclic AMP (2-10 microM) in S49 cells and thymocytes, suggesting that similar regulatory mechanisms act on this response in both types of cell. The data demonstrate that the basal [Ca2+]i and phosphoinositide metabolism is similar in both the normal cells and their transformed counterparts. In addition, they suggest that the activated Con A receptors generate very similar signals in the two cell types, and that any perturbations of primary signal transduction to the secondary phosphoinositide and [Ca2+]i responses in the S49 phenotype are quantitative rather than qualitative.     

Enhanced carrier-mediated lactate entry into isolated hepatocytes from starved and diabetic rats

Hepatic plasma membrane lactate transport was studied in isolated hepatocytes prepared from fed, starved, and streptozotocin diabetic rats. Carrier-mediated lactate entry was determined using the lactate transport inhibitors alpha-cyano-3-hydroxycinnamate and D-3-hydroxybutyrate and was significantly greater in hepatocytes from starved compared to fed rats and in hepatocytes from diabetic fed compared to fed rats. The saturable component of lactate entry which corresponds to carrier-mediated transport was higher in the starved than in the fed state with results from diabetic fed being intermediate between the two. Insulin treatment prevented the increment in carrier-mediated lactate transport observed in hepatocytes from diabetic fed rats. The data indicate that hepatic plasma membrane lactate transport is increased under conditions of starvation and diabetes mellitus. This may partly explain the increased gluconeogenic flux under these conditions.     

Design of an indicator of intracellular free Na+ concentration using 19F-NMR

The development is described of an Na+ chelator with appropriate properties for an indicator of intracellular free Na+ concentration ([Na+]i). The new indicator, FCryp-1, is a tribenzo derivative of the parent (2:2:1) cryptand structure, incorporating the same F-substituted dibenzo 19F-NMR reporter group as the free [Ca2+] indicator, 5FBAPTA (Smith, G.A., Hesketh, T.R., Metcalfe, J.C., Feeney, J. and Morris, P.G. (1983) Proc. Natl. Acad. Sci., USA 80, 7178-7182). FCryp-1 has appropriate affinity for Na+ (KNa = 10(1.3) M-1) and selectivity over other intracellular cations (KK; KCa; K Mg less than 10(-1) M(-1)) for a [Na]i indicator. There is an 19F-NMR chemical shift of 2.00 ppm between free FCryp-1 and the Na-FCryp-1 complex which provides a direct read out of free [Na+]. FCryp-1 carries four carboxylate groups to confer aqueous solubility which can be esterified with acetoxymethyl groups to render the indicator membrane permeant. Experiments on pig lymphocytes loaded with FCryp-1 gave an indicated [Na+]i of 13.8 +/- 1.8 mM (n = 4). The FCryp-1 structure can also be readily modified to provide fluorescent [Na+]i indicators.