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E K Matthews

Publications and source records attributed to E K Matthews.

At least 37 records · Page 2Linked to original sources
PubMed1987

Particle motion in single acinar cells observed by microscope laser light scattering spectroscopy.

We report here the direct observation of the motion of cytoplasmic subcellular organelles and macromolecules within single, metabolically active, pancreatic acinar cells using microscope laser-light scattering spectroscopy (MLLSS). The relative amount and the "effective diffusion coefficient" of the mobile particles shows a marked difference in magnitude between the apical and basal regions of the cell. Secretory stimulation evoked by the cholinergic agonist bethanechol induces changes in the relative motion in the cytoplasm of approximately one fifth of the acinar cells. This study demonstrates the feasibility and utility of a novel technique, MLLSS, for the analysis of intracellular events in regions as small as (2 micron)3 in single, granule secreting cells. It also shows MLLSS to be a powerful tool for the detection and measurement of altered motion in discrete subcellular regions of small mammalian cells after biochemical and pharmacological manipulations.

Animals↗
PubMed1987

Control of secretory granule interaction and exocytosis in pancreatic cells.

Application of the laser-based technique of photon correlation spectroscopy to an in vitro study of the ionic stability and interaction kinetics of zymogen granules isolated from rat exocrine pancreas is described here. In addition the separation from pancreatic acinar cell cytosol of a factor which stabilizes isolated zymogen granules and inhibits cation-induced granule aggregation is outlined. The basis of this action and the significance of the cytosolic inhibitory factor in the regulation of granule mobility and exocytosis in vivo is discussed.

Animals↗
PubMed1987

Failure of the Bactec 460 radiometer to detect Cryptococcus neoformans fungemia in an AIDS patient.

Cryptococcus neoformans fungemia occurred in a patient with the acquired immunodeficiency syndrome (AIDS). The BACTEC 460 radiometer failed to detect Cryptococcus neoformans in eight aerobic BACTEC 6B culture bottles inoculated with the patient's blood. The diagnosis of cryptococcemia was established by terminal (seven-day) subculturing of 6B broth to chocolate agar, which was positive for all eight radiometrically negative blood culture bottles. It appears that radiometric measurement is not optimal for the laboratory detection of cryptococcal fungemia.

Acquired Immunodeficiency Syndrome↗
PubMed1984

The control of 86Rb efflux from rat isolated pancreatic islets by the sulphonylureas tolbutamide and glibenclamide.

The efflux of 86Rb from rat isolated pancreatic islets preloaded with the isotope and perifused in vitro, has been used to monitor the effects of sulphonylureas on the potassium permeability, Pk, of pancreatic beta-cells. Tolbutamide (5 microM to 5 mM) had a dual effect, causing initially a decrease in 86Rb efflux (the 'on' response) which was rapidly superseded on drug removal by a large phasic increase in 86Rb efflux (the 'off' response). Each kinetic response had a different dose-dependency: the 'on' response was half-maximal at tolbutamide concentrations of 0.02 mM, maximal at 0.2 mM and decreased by concentrations greater than 0.2 mM whereas the 'off' response was half-maximal at 0.07 mM, maximal at 0.7 mM, with further increases in concentration (up to 5 mM) causing no further change in magnitude. Analysis of the time- and concentration-dependency of tolbutamide action, by presenting increasing concentrations (0 to 1.4 mM) of tolbutamide as a ramp or step function, established a critical dependence of the kinetics of 86Rb efflux during and after exposure to tolbutamide upon the initial rate of increase of the tolbutamide concentration rather than its final steady state. In the presence of quinine (10 microM), D600 (50 microM), or tetraethylammonium (20 mM), the secondary increase in 86Rb following tolbutamide (0.7 mM) removal was totally inhibited. Co2+ (2.56 mM) not only blocked the secondary 'off' response but also potentiated the initial 'on' response of tolbutamide. Glibenclamide produced a rapid decrease in 86Rb efflux but at a much lower concentration (10 microM) than tolbutamide and with no 'off' response apparent over a wide range of concentration (1 to 100 microM); moreover the decrease in 86Rb efflux was sustained and only slowly reversible. It is concluded that tolbutamide has two opposing actions on islet beta-cell 86Rb efflux, and therefore PK: (i) a tendency to increase a calcium-sensitive PK by stimulating calcium entry into the cell and (ii) a decrease in PK that may be due to a direct effect on the calcium-sensitive PK itself. The more sustained pharmacological action of glibenclamide is explained by the longer-lasting decrease in PK that it produces.

Animals↗
PubMed1984

Efflux of 86Rb from rat and mouse pancreatic islets: the role of membrane depolarization.

The efflux of 86Rb from rat or mouse perifused islets preloaded with the isotope has been used as an index of the potassium permeability of the islet beta-cell membrane. Cellular transmembrane potentials were altered by changing [K]O or by direct electrical stimulation and the effects on potassium permeability examined. Omission of KCl from the medium perifusing rat islets induced a biphasic change in 86Rb efflux, a brief decline being superseded by a pronounced increase in efflux. Re-introduction of KCl, 4.7 mM, caused a further increase in 86Rb efflux preceding a return to control values. Increasing [K]O from 4.7 mM to 10 mM, 20 mM or 47 mM caused a phasic increase in 86Rb efflux with the magnitude of both the peak and average rate of efflux being dependent upon the extent of the change in [K]O. The increase in 86Rb efflux produced by [K]O, 47 mM, was attenuated by Co2+, 2.56 mM (51% inhibition) or quinine, 10 microM (47% inhibition), but efflux remained significantly (P less than 0.001) above control values. Electrical stimulation of single microdissected mouse pancreatic islets by currents of 0.1 to 0.5 mA evoked a rapid, phasic increase in 86Rb efflux. The magnitude of the response was unaffected by EGTA, 2 mM, or nupercaine, 100 microM. These observations are discussed in relation to the mechanisms controlling the potassium permeability, membrane potential and insulin secretion of the pancreatic islet beta-cell. It is concluded that beta-cell depolarization by a raised [K]0 increases potassium permeability and efflux by at least two mechanisms: (i) a calcium-dependent potassium efflux triggered by an increase in [Ca]i and (ii) an activation of voltage-sensitive potassium channels which occurs even when the calcium-dependent potassium permeability is blocked.

Animals↗
PubMed1984

Photodynamic effects of erythrosine on the smooth muscle cells of guinea-pig taenia coli.

Photon activation of the halogenated fluorescein derivative erythrosine caused a marked calcium-dependent contraction of the smooth muscle cells of the guinea-pig taenia coli superfused in vitro. Neither high intensity illumination alone (up to 5 X 10(4) lux) nor erythrosine alone (up to 2 X 10(-4) M) altered the tone of the taenia or its ability to respond to carbachol (5 X 10(-5) M); photo-irradiation of erythrosine before tissue contact was also ineffective. The magnitude of the photodynamic contraction was dependent upon the concentration of erythrosine, the intensity and wavelength of the incident light, and the presence of oxygen; indirect effects via neurotransmitter release or cyclo-oxygenase activation were specifically excluded. The photodynamic response was blocked by zero-[Ca]o and addition of EGTA (1 mM) but not by omission of [Mg]o or a decrease in [Cl]o or [Na]o. D600 (methoxyverapamil) 10(-5) M, or a ten fold increase in [Mg]o, to 11.3 mM, partly inhibited the photodynamic contraction at low, but not high, light intensities. These observations are consistent with the following sequence of events: (i) photo-activation of the erythrosine molecule, (ii) the generation of highly reactive singlet oxygen, (iii) local peroxidation of cell membrane proteolipid, (iv) increased membrane permeability to Ca2+, (v) the influx of Ca2+ and, (vi) muscle contraction. It is concluded that the photodynamic action of erythrosine presents a novel method for modulation of membrane calcium permeability, and hence [Ca]i, not only in smooth muscle but possibly in other cells as well, e.g., secretory, epithelial and myocardial cells.

Action Potentials↗
PubMed1982

Biochemical and biophysical characterization of insulin granules isolated from rat pancreatic islets by an iso-osmotic gradient.

The size and polydispersity of insulin granules isolated from rat pancreatic islets by centrifugation on a linear iso-osmotic gradient (300 mosM) have been characterized by quasi-elastic light scattering and photon correlation spectroscopy. The separation of granules by the linear gradient technique was compared directly to isolation on discontinuous gradients of hypertonic sucrose (300-1950 mosM) and the greater efficiency of separation assessed by parallel measurements of protein, insulin, cytochrome oxidase and beta-glucuronidase. Granules isolated from pancreatic beta-cells had a mean particle diameter of 342 nm, buoyant density of 1.104, hydrated mass of 23 femtograms and maximal insulin content of 8-9.6 . 10(5) molecules per granule.

Animals↗
PubMed1982

Membrane potential changes of mouse adrenal zona fasciculata cells in response to adrenocorticotropin and adenosine 3',5'-monophosphate.

ACTH superfused onto mouse adrenal zona fasciculata tissue caused a transient, dose-dependent membrane depolarization. The log of the dose of ACTH was linearly related to the magnitude of depolarization. The onset of depolarization was rapid and dose dependent. Resting membrane potential changes observed after ACTH were blocked by CoCl2 but not tetrodotoxin or 4-aminopyridine, indicating that these depolarizations were dependent primarily on transmembrane Ca++ flux. CoCl2 also significantly blocked ACTH-stimulated adrenal steroid production; 4-aminopyridine had a much smaller and greatly delayed effect, whereas tetrodotoxin had no detectable effect on steroidogenesis. cAMP administration to adrenal zona fasciculata cells elicited transient, dose-dependent membrane depolarizations, which closely resembled those observed after ACTH treatment. In contrast to ACTH, CoCl2 did not block the cAMP-induced depolarization. These and other studies indicate that ACTH initiates a complex series of events by which steroidogenesis is stimulated. One mechanism may involve a change in membrane permeability to Ca++ independently of cAMP generation; a second mechanism may involve the activation of adenylate cyclase which subsequently influences the membrane conductance of the fasciculata cell membrane.

4-Aminopyridine↗
PubMed1981

The calcium antagonistic effects of cyproheptadine on contraction, membrane electrical events and calcium influx in the guinea-pig taenia coli.

1 The ability of cyproheptadine (Cph) to inhibit membrane translocation of calcium in smooth muscle was investigated by studying the drug's action on contraction, electrical activity and calcium influx in the guinea-pig taenia coli.2 Cph >/= 10(-6)M reduced the amplitude of normal spontaneous contractions and concurrently decreased the number of action potentials occurring with each slow-wave of depolarization (sucrose-gap recordings). These inhibitory effects of Cph were antagonized by increasing the medium [Ca] three fold to 7.68 mM.3 Intracellular recordings showed that Cph >/= 2 x 10(-6)M decreased the amplitude and extended the duration of the action potential. These effects were only partially reversible in normal medium whereas large overshooting action potentials were again seen in 7.68 mM Ca medium.4 High frequency mechanical activity was produced by inclusion of veratridine 5 x 10(-6)M in the perfusate. Low concentrations of Cph (>/= 10(-7)M) reduced the amplitude of such contractions at a faster rate than they did normal spontaneous contractions.5 At concentrations between 10(-7) and 10(-6)M, Cph fully reduced the tonic component of contractions elicited in 112 mM isotonic KCl whilst having little or no effect on either (i) the initial phasic KCl contraction or (ii) the ;repolarization contracture' normally produced on wash-out of the KCl or (iii) the spontaneous contractions before and after KCl treatment. In contrast, at Cph 2 x 10(-6)M, the repolarization contracture, as well as the isotonic KCl contraction, was totally blocked whereas spontaneous contractions were still unaffected. Progressively higher Cph concentrations inhibited all components of this contractile cycle.6 Dose-response curves for the rate of drug-induced relaxation of tonic contractures produced in hypertonic 42.7 mM high-potassium medium, showed the calcium antagonistic potency of Cph to be intermediate between that of chlorpromazine and D600. The minimum Cph concentration for effect lay between 1 and 5 x 10(-7)M, and the effects of Cph 2 x 10(-6)M (approximately the ID(50)) were totally antagonized by 12.8 mM Ca.7 By means of a lanthanum wash procedure, Cph >/= 2 x 10(-6)M was found to decrease the (45)Ca uptake occurring into strips of taenia coli in normal medium, although the maximum effect (at Cph 10(-5)M) amounted to only 25% inhibition of the uptake occurring into control strips (also found with D600). The increased uptake occurring in hypertonic 44.7 mM high-potassium medium was inhibited in a dose-dependent manner by Cph 1 x 10(-7)M.8 The results are consistent with an action of Cph in reducing the flow of Ca(2+) through voltage-dependent Ca channels in the smooth muscle cell membrane. It is suggested that the interaction of Cph molecules with such sites is dependent upon membrane potential as well as drug concentration.

Animals↗
PubMed1980

Calcium exchangeability in subcellular fractions of pancreatic islet cells.

The distribution and exchangeability of calcium within subcellular compartments of rat pancreatic islet cells was determined in pulse-chase experiments following isotopic labelling with 45Ca2+. In unstimulated islets the mitochondrial fraction showed the greatest, and the insulin secretory granule fraction the least, uptake of 45Ca2+; subsequently the rate of loss from each compartment during 120 min was in the order mitochondrial greater than microsomal greater than secretory granule fraction. On exposure to D-glucose, 16.8 mM, the 45Ca labelling of all 3 subcellular compartments was increased after 5 and 30 min stimulation. In contrast, theophylline 10 mM caused a significant decrease in mitochondrial 45Ca content with little effect on other compartments. These results are discussed in relation to the importance of calcium disposition, exchangeability, and mobility for the initiation and control of insulin secretion.

Animals↗
PubMed1980

Correlations between chanelled Na+ entry, Ca2 + fluxes and insulin release in pancreatic beta-cells.

The results of ion flux measurements and insulin release studies performed on isolated rat islets of Langerhans using veratridine and tetrodotoxin show that Na+ channels exist in the outer membrane of pancreatic beta-cells. From a pharmacological point of view these channels appear very similar, if not identical, to those present in nerve. The consequences of opening such channels are described and their possible involvement in the physiological regulation of insulin release discussed.

Animals↗
PubMed1980

Membrane surface interactions involved in insulin secretion.

Laser light-scattering techniques have been used to study the effects of polyanions on the time-dependent interaction of (i) polystyrene particles and (ii) insulin-containing granules isolated from pancreatic islets. New evidence of a major effect of polyanions on secretory granule aggregation is presented. The possible importance of intracellular polyanions in restricting the aggregation and hence fusion of secretory granules, especially in the presence of Ca2+, is discussed.

Animals↗
PubMed1979

Dynamic oscillations in the membrane potential of pancreatic islet cells.

Glucose and other metabolizable sugars which elicit insulin release from the beta-cell of the pancreatic islet induce repetitive oscillations in the beta-cell transmembrane potential. Upon each phasic depolarization are superimposed rapid fluctuations in potentials, i.e. 'action potentials' or 'spikes' which occur as bursts of electrical activity; the duration and frequency of each burst is a function of glucose concentration. These established electrophysiological features of glucose-islet cell interaction are described in detail together with a consideration of their possible molecular and ionic basis. Based on these observations, a dynamic mathematical computer model of the beta-cell membrane electrical behaviour is presented which utilizes the Goldman equation extended to include divalent ions. The model illustrates how the ionic mechanisms deduced from experimental observations can account for the electrical patterns produced by the beta-cells in the presence of D-glucose; it also allows systematic changes to be made in a number of state variables in order to assess their relative importance and possible contribution to the integrated processes actually observed. Finally, distinction is made between aspects of the model which are well supported by experimental results and those areas which require further analysis.

Animals↗
PubMed1978

Developmental changes in rat adrenocortical cell membrane potential.

Resting membrane potentials of zona fasciculata-reticularis cells of the rat adrenal gland varied with age. The mean membrane potentials of newborn rat adrenal cells was -56.4 +/- 0.7 mV in the first week of life. The mean potential increased slightly to -61.9 +/- 0.8 mV in the second week and then decreased with age to a mean of -38.5 +/- 0.8 mV in 25--50 week old rats and of -25.9 +/- 1.9 mV in 100 week old rats. The changes in membrane potential may correlate with the indices of adrenocortical growth and activity.

Adrenal Cortex↗