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Brij L. Gupta

Bio: Brij L. Gupta is an academic researcher from University of Cambridge. The author has contributed to research in topics: Electron microprobe & Microprobe. The author has an hindex of 21, co-authored 28 publications receiving 1354 citations.

Papers
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Journal ArticleDOI
18 Nov 1976-Nature
TL;DR: In this paper, the authors used electron-probe X-ray microanalysis to measure the intracellular ionic concentrations and found that Na, K and Cl are not uniformly distributed within the cells, and that the basal lamina is not entirely a passive membrane open to small ions.
Abstract: STUDIES of fluid transport in epithelia have in general been limited to measurements of the composition of the transported fluid and the electrochemical gradients against which transport occurs1–3. We have now used electron-probe X-ray microanalysis to measure the intracellular ionic concentrations. The data show that Na, K and Cl are not uniformly distributed within the cells; that the basal lamina is not entirely a passive membrane open to small ions, and that, in the particular epithelium studied, the stimulation of secretion greatly increases the intracellular Na concentration. In addition, the results do not support the standing gradient theory of fluid secretion.

111 citations

Journal ArticleDOI
02 Mar 1978-Nature
TL;DR: In this article, electron microprobe X-ray analysis was used to measure the concentration profiles of Na, K, Cl, Ca, S and P in the mucosal tissue of rabbit ileum.
Abstract: THE absorption of many solutes and water by the intestinal mucosa is linked passively to an active transport of Na+ to produce an absorbate which is isotonic with the capillary plasmal1,2. Since Curran3 first proposed a double membrane model with a hypertonic compartment within the tissue, it has generally been accepted that the primary sites of Na+ transport4,5 and solute–water coupling are the lateral intercellular spaces (LIS) within the epithelium (for reviews see refs 6 and 7). Several theoretical models have been proposed to explain how the secretion of Na+ into LIS generates flow of water, but the sites within the tissue where the final isotonicity of the absorbate is achieved remain controversial8–15. This is chiefly because it has not been possible directly to measure the profiles of ionic concentrations in the US and surrounding tissue compartments. Indirect evidence has suggested that the extracellular spaces in gall bladder16, feline intestine17 and rabbit ileum18 contain higher concentrations than those found in external bathing solutions. We have now used electron microprobe X-ray analysis19–22 of frozen-hydrated sections to measure the concentration profiles of Na, K, Cl, Ca, S and P in the mucosal tissue of rabbit ileum. The results establish the hypertonicity of the fluid in the LIS and the concentration gradients of Na, K and Cl in the cells and in the LIS.

107 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed the mass loss from biological tissue sections during electron microprobe irradiation was observed by means of a silicon semiconductor detector set to record continuum X radiation.
Abstract: SUMMARY The loss of mass from biological tissue sections during electron microprobe irradiation was observed by means of a silicon semiconductor detector set to record continuum X radiation. The rate of loss depended on several factors, conspicuously on specimen temperature. In accord with earlier observations with non-focused beams, most of the ‘immediate’ loss occurred within an electron dose of the order of 10−10 C/μm2.

102 citations

Journal ArticleDOI
TL;DR: The detailed structure of the cockroach spermatheca is described and discussed firstly as an example of an insect integumentary gland, and secondly, from the standpoint of its role in reproduction.
Abstract: . The detailed structure of the cockroach spermatheca is described and discussed firstly as an example of an insect integumentary gland, and secondly, from the standpoint of its role in reproduction. The gland comprises a cortical rank of separate secretory units, each associated with an epithelial duct cell responsible for receiving secreted materials and transporting them through the cuticular intima lining the reproductive tract. Secretory activity is cyclic, and the probable mode of elaboration and release of secretory material is described, together with the fine structure of the markedly differing intimas associated respectively with the glandular and conducting units.

101 citations

Journal ArticleDOI
TL;DR: The lepidopteran midgut is a model for the oxygendependent, electrogenic K+ transport found in both alimentary and sensory tissues of many economically important insects and it is concluded that the K+ pump is sited on the goblet cell apical membrane and that K+ follows a nonmixing pathway via only part of the goblt cell cytoplasm.
Abstract: The lepidopteran midgut is a model for the oxygendependent, electrogenic K+ transport found in both alimentary and sensory tissues of many economically important insects. Structural and biochemical evidence places the K+ pump on the portasome-studded apical plasma membrane which borders the extracellular goblet cavity. However, electrochemical evidence implies that the goblet cell K+ concentration is less than 50mm. We used electron probe X-ray microanalysis of frozenhydrated cryosections to measure the concentration of Na, Mg, P, S, Cl, K, Ca and H2O in several subcellular sites in the larval midgut ofManduca sexta under several experimental regimes. Na is undetectable at any site. K is at least 100mm in the cytoplasm of all cells. Typicalin vivo values (mm) for K were: blood, 25; goblet and columnar cytoplasm, 120; goblet cavity, 190; and gut lumen, 180. The high K concentration in the apically located goblet cavity declined by 100mm under anoxia. Both cavity and gut fluid are Cl deficient, but fixed negative charges may be present in the cavity. We conclude that the K+ pump is sited on the goblet cell apical membrane and that K+ follows a nonmixing pathway via only part of the goblet cell cytoplasm. The cavity appears to be electrically isolated in alimentary tissues, as it is in sensory sensilla, thereby allowing a PD exceeding 180 mV (lumen positive) to develop across the apical plasma membrane. This PD appears to couple K+ pump energy to nutrient absorption and pH regulation.

96 citations


Cited by
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Journal ArticleDOI
TL;DR: Water is the most abundant component of biological material, but it is systematically excluded from conventional electron microscopy, because water evaporates rapidly under the vacuum conditions of an electron microscope.
Abstract: Water is the most abundant component of biological material, but it is systematically excluded from conventional electron microscopy. This is because water evaporates rapidly under the vacuum conditions of an electron microscope. Cryoelectron microscopy has long been seen as a possible avenue to overcome this limitation, but until recently the direct observation of frozen-hydrated specimens was relatively unsuccessful because of a number of serious difficulties. These were, in particular, due to the absence of a good cryospecimen holder, the inherently low contrast of hydrated specimens and the structural damage due to ice crystals formed during freezing. As a consequence, the cryomethods which have flourished in electron microscopy during the last 20 years were not aimed at preserving the hydration of the specimen in the electron microscope. Freezing was only used as an aid to preparation. The objects ultimately observed in the electron microscope were dry and at room temperature. Such cryomethods have recently been reviewed in detail (Robards and Sleytr 1985).

2,137 citations

Journal ArticleDOI
TL;DR: The use of synthetic organic insecticides developed during the last half of this century may pose risks to human health and can cause environmental damage, Consequently, interest has developed in using alternative strategies for insect pest management, including Bacillus thuringiensis toxins as insecticides.
Abstract: The use of synthetic organic insecticides developed during the last half of this century may pose risks to human health and can cause environmental prob­ lems. Consequently, interest has developed in using alternative strategies for insect pest management. One contemporary approach that has received atten­ tion is the development of Bacillus thuringiensis (Bt) toxins as insecticides. B. thuringiensis, a gram-positive bacteria, produces a proteinaceous paraspor­ al crystalline inclusion during sporulation. Upon ingestion by insects, this crystalline inclusion is solubilized in the midgut, releasing proteins called S-endotoxins. These proteins (protoxins) are activated by midgut proteases, and the activated toxins interact with the larval midgut epithelium causing a disruption in membrane integrity and ultimately leading to insect death. In spite of significant efforts directed towards the study of Bt, its use in pest control is restricted, in part because of the selectivity of Bt and in part because of its moderate efficacy. Attempts to improve these two qualities have met with only moderate success because inadequate effort has been devoted to understanding the molecular basis of selectivity and insecticidal properties of these toxins.

827 citations

Journal ArticleDOI
TL;DR: The principles of microscopy principles in light microscopy scanning techniques in electron microscopy and their applications in transmission/scanning and digital holographic microscopy are explained.
Abstract: principles and techniques of electron microscopy principles and techniques of electron microscopy electron microscopy and optics: general textbooks principles and techniques of electron microscopy principles and techniques of electron microscopy principles and techniques of digital holographic microscopy scanning electron microscopy cathodoluminescence of quartz introduction to transmission/scanning transmission principles and technique of fluorescence microscopy by m principles and techniques of electron microscopy: volume 1 principles of the phase contrast (electron) microscopy principles and techniques of electron microscopy lecture 1 the principles of microscopy principles in light microscopy scanning techniques in electron microscopy

677 citations

Book
14 Jul 1975

644 citations

Journal ArticleDOI
17 Jul 1981-Science
TL;DR: The existence of a symbiotic association between vestimentiferan tube worms from deep-sea hydrothermal vents and chemoautotrophic sulfur-oxidizing prokaryotes, based on histological and enzymatic evidence, is suggested.
Abstract: The existence of a symbiotic association between vestimentiferan tube worms from deep-sea hydrothermal vents and chemoautotrophic sulfur-oxidizing prokaryotes, based on histological and enzymatic evidence, is suggested.

631 citations