The regulation of transepithelial water permeability in toad urinary bladder is believed to involve a cycling of endocytic vesicles containing water transporters between an intracellular compartment and the cell luminal membrane. Endocytic vesicles arising from luminal membrane were labeled selectively in the intact toad bladder with the impermeant fluid-phase markers 6-carboxyfluorescein (6CF) or fluorescein-dextran. A microsomal preparation containing labeled endocytic vesicles was prepared by cell scraping, homogenization, and differential centrifugation. Osmotic water permeability was measured by a stopped-flow fluorescence technique in which microsomes containing 50 mM mannitol, 5 mM K phosphate, pH 8.5 were subject to a 60-mM inwardly directed gradient of sucrose; the time course of endosome volume, representing osmotic water transport, was inferred from the time course of fluorescence self-quenching. Endocytic vesicles were prepared from toad bladders with hypoosmotic lumen solution treated with (group A) or without (group B) serosal vasopressin at 23 degrees C, and bladders in which endocytosis was inhibited by treatment with vasopressin at 0-2 degrees C (group C), or with vasopressin plus sodium azide at 23 degrees C (group D). Stopped-flow results in all four groups showed a slow rate of 6CF fluorescence decrease (time constants 1.0-1.7 s for exponential fit) indicating a component of nonendocytic 6CF entrapment into sealed vesicles. However, in vesicles from group A only, there was a very rapid 6CF fluorescence decrease (time constant 9.6 +/- 0.2 ms, SEM, 18 separate preparations) with an osmotic water permeability coefficient (Pf) of greater than 0.1 cm/s (18 degrees C) and activation energy of 3.9 +/- 0.8 kcal/mol (16 kJ/mol). Pf was inhibited reversibly by greater than 60% by 1 mM HgCl2. The rapid fluorescence decrease was absent in vesicles in groups B, C, and D. These results demonstrate the presence of functional water transporters in vasopressin-induced endocytic vesicles from toad bladder, supporting the hypothesis that water channels are cycled to and from the luminal membrane and providing a functional marker for the vasopressin-sensitive water channel. The calculated Pf in the vasopressin-induced endocytic vesicles is the highest Pf reported for any biological or artificial membrane.

Green's functions based on truncated periodicity play an important role in the efficient analysis of radiation from, or scattering by, phased-array antennas, frequency selective surfaces and related applications. Such Green's functions exploit the equivalence between summation over the contributions from individual elements in an array and their collective treatment via Poisson summation in terms of an infinite series of Floquet waves (FW). While numerous explorations have been carried out in the frequency domain (FD), much less has been done for transient excitation. In order to gain understanding of the FW critical parameters and phenomenologies governing time-domain (TD) periodicity, we consider the simple canonical problem of radiation from an infinite periodic line array of sequentially pulsed axial dipoles. This problem can be solved in closed form and also by a variety of alternative representations, which include inversion from the FD, spectral decomposition into TD plane waves, the complex space-time analytic signal formulation, and the Cagniard-de Hoop method. These alternatives, some of which apply traditionally only for nondispersive TD events, are shown to still work here because of the special character of the FW dispersion. Particular attention is given to evanescent TD-FW's and their transition through cutoff. Asymptotic techniques grant insight into the TD-FW behavior by identifying their instantaneous frequencies, wavenumbers, and other physics-based parameterizations. A basic question concerns the definition of what constitutes a physically 'observable' (causal, etc.) TD-FW. The proposed answer is based on consistency among models arrived at by alternative routes.

A study of pulsed radiation by a phased semi-infinite periodic planar array of dipoles was presented. The explanation of phenomenology associated with truncated time domain (TD)-floquet waves (FW) and truncation-induced diffraction was presented in terms of instantaneous frequencies aided by asymptotic parameterization. Total field expression was obtained by applying the infinite Poisson summation formula to the doubly-infinite sum over the radiation by each dipole.

This chapter outlines the history of the study of anaerobic metabolism during exercise. The emphasis is on the early origins and progression of studies on phosphagen and glycolytic metabolism. Although the topic is "anaerobic" metabolism, the interrelationship between oxygen and lactic acid production is considered to be of prime importance. The prelactic acid era (1808-1907) is responsible for the discovery of lactic acid and its relationship with the physical activity and hypoxia. The era between 1926 and 1932 is considered as "the revolution in muscle physiology" because of the experiments performed on the "phosphagens" and the discovery of muscle adenylic acid. In 1962, D.F. Cain and R.E. Davies provided proof that ATP (Adenosine Triphosphate) is the immediate energy donor for muscle contraction. In 1980, Glenn Gaesser and George Brooks utilized 14C-tracers, indirect calorimetry, and two-dimensional chromatography to trace the paths of lactate and glucose disposal during recovery from exhausting exercise. The year 1984 is recognized for the observation of lactate production in canine muscle in situ when intramuscular PO2 is apparently above the critical value for mitochondrial oxidative phosphorylation. In 1994, monocarboxylate transport protein (MCT)encoding gene was sequenced and cloned. In 1998, magnetic resonance spectroscopy (MRS) was utilized to show lactate production and the net release from fully aerobic, working human skeletal muscle, followed by the cloning and sequencing of four new MCT isoforms and the description of tissue variability in MCT isoform expression.

We have begun a systematic investigation of the time domain (TD) behavior of Green's functions which are relevant for the characterization of truncated planar periodic arrays, with emphasis on the TD Floquet waves (FW) in the propagating and evanescent parameter regimes. Our principal aim is to understand the TD wave physics and phenomenologies on simple prototypes, invoking various methods that synthesize the solution from different perspectives. The first prototype, an infinite phased periodic line array of axial dipole radiators arranged along the axis of a cylindrical (/spl rho/,z) coordinate system has been studied in Felsen and Capolino (1998). This prototype is a basic building block for transverse truncated plane arrays formed by a finite number of infinite line sources, which has so far been studied only in the frequency domain (Capolino et al. 1998). Truncation aIong the axis of a phased line array of dipoles is explored in this paper for the frequency domain (FD) and TD. This modification of the infinite line dipole array leads to a new set of FD and TD truncation phenomena.

Previous time domain (TD) studies are extended to an infinite periodic sequentially pulsed planar array. This canonical prototype is shown to be simple enough the admit closed form exact solutions. Preliminary numerical results demonstrate the efficiency of the TD-FW algorithms.

Biogenic volatile organic carbon (BVOC) emissions are an important component of the global BVOC budget, contributing more than 90%. Emissions vary with species and vegetation type; therefore to produce accurate global budgets data is required from different vegetation types. This study investigates BVOC emissions from savannas, Kalahari woodlands, Kalahari open shrublands and Mopane woodlands in southern Africa. BVOC emission samples from individual species were collected using leaf cuvettes and the BVOC concentrations were determined by GC-FID/MS. Ten of the 14 woodland species measured were high isoprene emitters, while two showed high monoterpene emission capacities. Landscape average isoprene emission capacities were estimated to be as high as 9, 8 and 1mg Cm-2h-1 for savannas, woodlands and shrub lands, respectively. The monoterpene emission capacity for Mopane woodlands were estimated at almost 3mg Cm-2h-1, while for other landscapes it varied between 0.04 and 3mg Cm-2h-1. Isoprene and monoterpene emissions at a savanna site in South Africa showed a seasonal variation, which is more pronounced for isoprene. During the winter (June-September) estimated emissions were <10mg Cm-2d-1, with peak emissions (ranging between 20 and 80mg Cm-2d-1) occurring during the summer months (December-March) when foliar density peaked. The total BVOC emission from southern African (south of the Equator) savannas was estimated to be in the range of 18-74Tg Cyr-1. Copyright © 2002 Elsevier Science Ltd.

The NaCl reflection coefficient in proximal tubule has important implications for the mechanisms of near isosmotic volume reabsorption. A new fluorescence method was developed and applied to measure the transepithelial (sigma NaClTE) and basolateral membrane (sigma NaClcl) NaCl reflection coefficients in the isolated proximal straight tubule from rabbit kidney. For sigma NaClTE measurement, tubules were perfused with buffers containing 0 Cl, the Cl-sensitive fluorescent indicator 6-methoxy-N-[3-sulfopropyl] quinolinium and a Cl-insensitive indicator fluorescein sulfonate, and bathed in buffers of differing cryoscopic osmolalities containing NaCl. The transepithelial Cl gradient along the length of the tubule was measured in the steady state by a quantitative ratio imaging technique. A mathematical model based on the Kedem-Katchalsky equations was developed to calculate the axial profile of [Cl] from tubule geometry, lumen flow, water (Pf) and NaCl (PNaCl) permeabilities, and sigma NaClTE. A fit of experimental results to the model gave PNaCl = (2.25 +/- 0.2) x 10(-5) cm/s and sigma NaClTE = 0.98 +/- 0.03 at 23 degrees C. For measurement of sigma NaClbl, tubule cells were loaded with SPQ in the absence of Cl. NaCl solvent drag was measured from the time course of NaCl influx in response to rapid (less than 1 s) Cl addition to the bath solution. With bath-to-cell cryoscopic osmotic gradients of 0, -60, and +30 mosmol, initial Cl influx was 1.23, 1.10, and 1.25 mM/s; a fit to a mathematical model gave sigma NaClbl = 0.97 +/- 0.04. These results indicate absence of NaCl solvent drag in rabbit proximal tubule. The implications of these findings for water and NaCl movement in proximal tubule are evaluated.

Osmotic water permeability (Pf) in toad bladder is regulated by the vasopressin (VP)-dependent movement of vesicles containing water channels between the cytoplasm and apical membrane of granular cells. Apical endosomes formed in the presence of serosal VP have the highest Pf of any biological or artificial membrane (Shi and Verkman. 1989. J. Gen. Physiol. 94:1101-1115). We examine here: (a) the influence of protein kinase A and C effectors on transepithelial Pf (Pfte) in intact bladders and on the number and Pf of labeled endosomes, and (b) whether endosome Pf can be modified physically or biochemically. In paired hemibladder studies, Pfte induced by maximal serosal VP (50 mU/ml, 0.03 cm/s) was not different than that induced by 8-Br-cAMP (1 mM), forskolin (50 microM), VP + 8-Br-cAMP, or VP + forskolin. Pf was measured in endosomes labeled in intact bladders with carboxyfluorescein by a stopped-flow, fluorescence-quenching assay using an isolated microsomal suspension; the number and Pf (0.08-0.11 cm/s, 18 degrees C) of labeled endosomes was not different in bladders treated with VP, forskolin, and 8-Br-cAMP. Protein kinase C activation by 1 microM mucosal phorbol myristate acetate (PMA) induced submaximal bladder Pfte (0.015 cm/s) and endosome Pf (0.022 cm/s) in the absence of VP, but had little effect on maximal Pfte and endosome Pf induced by VP. However, PMA increased by threefold the number of apical endosomes with high Pf formed in response to serosal VP. Pf of endosomes containing the VP-sensitive water channel decreased fourfold by increasing membrane fluidity with hexanol or chloroform (0-75 mM); Pf of phosphatidylcholine liposomes (0.002 cm/s) increased 2.5-fold under the same conditions. Endosome Pf was mildly pH dependent, strongly inhibited by HgCl2, but not significantly altered by GTP gamma S, Ca, ATP + protein kinase A, and phosphatase action. We conclude that: (a) water channels cycled in endocytic vesicles are functional and not subject to physiological regulation, (b) VP and forskolin do not have cAMP-independent cellular actions, (c) activation of protein kinase C stimulates trafficking of water channels, but does not increase the number of apical membrane water channels induced by maximal VP, and (d) water channel function is sensitive to membrane fluidity. By using VP and PMA together, large quantities of endosomes containing the VP-sensitive water channel are labeled with fluid-phase endocytic markers.