PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 968203

Ternary gas diffusion - in vitro studies.

H I Modell·L E Farhi
View original source ↗Export metadata ↓

Abstract

The purpose of these experiments was to compare diffusive gas movement in a two-gas system with that in a three-gas system. Gas mixtures of different compositions were placed initially on either side of a removable partition dividing a cylindrical lucite diffusion chamber, filled with 3 mm glass beads. This served to slow diffusion, minimize convective currents generated by removing the partition, and stabilize temperature within the chamber. In two-gas systems, after the partition was removed, oxygen equilibrated between the two parts of the chamber more rapidly in a helium environment than in a nitrogen environment, conforming with predictions based on binary gas laws. Results obtained with a three-gas system differed significantly from those obtained with the binary system. With 21% oxygen in belium initially in one half of the chamber and 21% oxygen in nitrogen in the other, PO2 rose transiently in the He-O2 side of the chamber. Qualitatively, similar results were obtained when the O2-N2 mixture was replaced by 100% nitrogen. Pressure in the system remained essentially constant. The possible mechanisms responsible for the PO2 rise were studied using a computer model of the system. This showed that movement of a given gas may be affected significantly by movement of other gases in the system. Hence, application of binary gas diffusion laws to systems containing more than two gases may lead to significant errors.

Explore related subjects

DiffusionGasesHeliumModels, BiologicalNitrogenOxygenJournal ArticleResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

H I Modell, L E Farhi. 1976. Ternary gas diffusion - in vitro studies.. https://doi.org/10.1016/0034-5687(76)90018-9

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1999

Growing pollen tubes possess a constitutive alkaline band in the clear zone and a growth-dependent acidic tip.

Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H+) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 microM or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

Diffusion↗
PubMed1999

Kramers' diffusion theory applied to gating kinetics of voltage-dependent ion channels.

Kramers' diffusion theory of reaction rates in the condensed phase is considered as an alternative to the traditional discrete-state Markov (DSM) model in describing ion channel gating current kinetics. Diffusion theory can be expected to be particularly relevant in describing high-frequency (>100 kHz) events in channel activation. The generalized voltage sensor of a voltage-dependent ion channel is treated as a Brownian motion particle undergoing spatial diffusion along a one-dimensional energy landscape. Two classes of energy landscapes are considered. The first class contains large barriers, which give rise to gating currents with two distinct time scales: the usual low-frequency decay, which can modeled with a DSM scheme, and a high-frequency component arising from intrastate relaxation. Large depolarizations reduce potential barriers to such a degree that activation rates are diffusion limited, causing the two time scales to merge. Landscapes of the second class are either featureless or contain barriers that are small compared to kT; these are termed "drift landscapes." These landscapes require a larger friction coefficient to generate slow gating kinetics. The high-frequency component that appears with barrier models is not present in pure drift motion. The presence of a high-frequency component can be tested experimentally with large-bandwidth recordings of gating currents. Topics such as frequency domain analysis, spatial dependence of the friction coefficient, methods for determining the adequacy of a DSM model, and the development of physical models of gating are explored.

Diffusion↗
PubMed1998

Studies of the internal flow process in polymers by 1H NMR microscopy at 500 MHz.

Nuclear Magnetic Resonance (NMR) microscopy was used to study the dynamics and diffusion of the internal water flow in erodible Hydroxypropylmethylcellulose (HPMC) and Polyvinylalcohol (PVA) polymers of pharmaceutical interest. Polymers in the form of tablets were hydrated at 37 degreesC continuously and monitored at regular intervals with a 500 MHz NMR microscope. The diffusion and spin-spin relaxation time (T2)-weighted images revealed that the gel layer was strongly attached to the core of the tablet in both HPMC and PVA polymers. Spatial distribution of self diffusion coefficients (SDCs) and T2 of the hydrating polymers were calculated from NMR microscopic images.

Diffusion↗