PubMed Health⌕ Search

PubMed · 6534092

Microcirculatory mass transfer.

Abstract

The dynamics of Krogh tissue cylinders and related structures are critically reviewed to determine the roles of underlying transport and reaction processes, and the interactions between them. Emphasis is put on the gaining of insight through efficient scaling procedures, and discussion is organized about the time constants characteristic of these structures and the processes occurring in them. The basis of discussion is a new analytic solution technique which provides a formal description of indefinitely large arrays of parallel interacting elements and which includes both axial diffusion and uniform convection as well as first or zero order reaction within each element. The solution has the form of an expansion in the eigenfunctions of a non-self-adjoint differential operator. Comparison of model predictions with previously available results identifies the useful parameter ranges of analytic approximations and determines the accuracy of existing numerical procedures.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

E N Lightfoot, A M Lenhoff. 1984. Microcirculatory mass transfer.. https://doi.org/10.1007/978-1-4684-4895-5_2

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

KEEP EXPLORING

Related citations

Identification of a novel Na+- and Cl--coupled transport system for endogenous opioid peptides in retinal pigment epithelium and induction of the transport system by HIV-1 Tat.

The endogenous opioid peptides enkephalins, dynorphins and endorphins consist of five or more amino acids. These peptides participate in a multitude of biological functions in mammalian cells by interacting with different subtypes of opiate receptors located on the plasma membrane and in the nucleus. Here we report on the identification of a new peptide transport system in the human retinal pigment epithelial (RPE) cells that transports a variety of endogenous opioid peptides with high affinity. We identified this novel, hitherto unrecognized, transport system when we were analysing the differential effects of Tat, the transacting factor encoded by HIV-1, on various transport processes in RPE cells. This transport system is markedly induced by Tat. This opioid transport system is energized by transmembrane Na+ and Cl- gradients and is distinct from any of the previously identified transport systems for opioid peptides in mammalian cells. Free amino acids, dipeptides, tripeptides and non-peptide opiate receptor antagonists are excluded by this newly identified transport system. The affinities of endogenous opioid peptides for this system are in the range of 0.4-40 microM. The identification of the high-affinity Na+- and Cl--coupled transport system in mammalian cells that is specific for endogenous opioid peptides and is induced by HIV-1 Tat is of significance not only to the biology of opioid peptides but also to the pathology of HIV-1 infection in humans.

Biological Transport, Active↗

Iron uptake by Escherichia coli.

Ferric iron is transported into Escherichia coli by a number of chelating compounds. Iron transport through the outer membrane by citrate, ferrichrome, enterobactin, aerobactin, yersiniabactin, and heme is catalyzed by highly specific proteins and across the cytoplasmic membrane by ABC transport systems with lower specificity. Transport across the outer membrane requires energy, which is provided by the proton motive force of the cytoplasmic membrane and transmitted to the outer membrane via the TonB-ExbB-ExbD proteins. Binding of substrates induces large long-range structural changes in the transport proteins, but does not open the channel. It is thought that the channel is opened by energy input from the cytoplasmic membrane. Although a basic understanding of how the transport proteins might function has been obtained from the crystal structures of three outer membrane proteins of E. coli and from many genetic and biochemical experiments, numerous fundamental questions still remain open. Transcription of the transport protein genes is regulated by the Fur protein, which when loaded with ferrous iron functions as a repressor. Fur also positively regulates genes of iron-containing proteins by repressing synthesis of an anti-sense RNA. Regulation of ferric citrate transport genes via a transmembrane device has become the paradigm of the regulation of a variety of systems, including the hypersensitivity response of plants to bacterial infections.

Biological Transport, Active↗

Spontaneous membrane transfer through homotypic synapses between lymphoma cells.

Formation of an immunological synapse by T, B, or NK cells is associated with an intercellular transfer of some membrane fragments from their respective target cells. This capture is thought to require effector cell activation by surface recognition of stimulatory ligand(s). However, spontaneous synaptic transfers between homotypic lymphoid cells has never been described. In this study, we show that without adding Ag, resting healthy lymphoid cells and several tumor cell lines are inactive. Conversely, however, some leukemia cell lines including the Burkitt's lymphoma Daudi continuously uptake patches of autologous cell membranes. This intercellular transfer does not involve cytosol molecules or exosomes, but requires cell contact. In homotypic Daudi cell conjugates, this occurs through immunological synapses, involves constitutive protein kinase C and mitogen-activated protein/extracellular signal-regulated kinase kinase activity and strongly increases upon B cell receptor activation. Thus, spontaneous homosynaptic transfer may reflect the hitherto unsuspected autoreactivity of some leukemia cell lines.

Biological Transport, Active↗