Plasma membrane passive diffusion through

Formation of Na+, K+-ATPase carrier molecules in the basolateral membrane of the tubular epithelial cells (promotes extrusion of Na+ ions from the cells and their movement into plasma by way of peritubular capillaries enhances the concentration gradient for passive diffusion through Na+ channels in the luminal membrane)... 

The unbound drug in the systemic circulation is available to distribute extravascularly. The extent of distribution is mainly determined by lipid solubility and, for weak organic acids and bases, is influenced by the pK3/pH-dependent degree of ionization because only the more lipid-soluble non-ionized form can passively diffuse through cell membranes and penetrate cellular barriers such as those which separate blood from transcellular fluids (cerebrospinal and synovial fluids and aqueous humour). The milk-to-plasma equilibrium concentration ratio of an antimicrobial agent provides a reasonably... 

Distribution is the phase in which the compound is carried to tissues by the bloodstream or lymphatic system. Compounds are usually first absorbed into the portal venous system after oral administration directing them to the liver where they may be removed (extracted/metabolized) (first-pass effect). The blood (plasma) level reflects the concentration at the target/receptor and is governed by distribution. Distribution depends on passage through membranes (passive diffusion, carrier mediated transport etc.) and may be limited by binding to blood proteins. 

Boron enters plant roots as undissociated boric acid. Significant differences in boron uptake occur, even when plants are grown under identical conditions. Recent findings indicate that the lipid composition of the plasma membrane can affect total boron uptake by a plant. Evidence also has been obtained indicating that boron enters plant cells in part by passive diffusion through the lipid bilayer of the plasma membrane... 

Plasmid DNA must penetrate the nuclear envelope to be transcribed for gene expression. Like a plasma membrane or endosomal membrane, the nuclear envelope constitutes an impenetrable barrier to highly charged macromolecules. Passive diffusion through the NPC is possible, but only for short DNAs of below 310 base pairs [182]. Without any assistance, only 1-2% of DNA can be transported to the nucleoplasm between the narrow gateway and the cytosolic digestion [183]. The disruption of the nuclear envelope during mitotic division is the only chance for free pDNA to enter the nucleoplasm. 

Figure 1 General pathways through which molecules can actively or passively cross a monolayer of cells. (A) Endocytosis of solutes and fusion of the membrane vesicle with the opposite plasma membrane in an active process called transcytosis. (B) Similar to A, but the solute associates with the membrane via specific (e.g., receptor) or nonspecific (e.g., charge) interactions. (C) Passive diffusion between the cells through the paracellular space. (C, C") Passive diffusion (C ) through the cell membranes and cytoplasm or (C") via partitioning into and lateral diffusion within the cell membrane. (D) Active or carrier-mediated transport of an otherwise poorly membrane permeable solute into and/or out of a cellular barrier.

In aqueous solution around pH 7, WR 1065 is doubly protonated (net charge Z = 2). Its uptake by mammalian cells is kinetically of first-order and increases with [H+]-1/2. This has been taken as evidence that the transport through plasma membrane probably occurs by a passive diffusion of the uncharged diamine (Calabro-Jones et al. 1988). 

In more recent attempts to map the cellular distribution of cisplatin, Beretta et al. (50) incubated human ovarian cancer cells (A2780) with cisplatin concentrations of up to 100 xM for 30 minutes and observed electron dense spots, identified as large platinum deposits, distributed in the cell cytoplasm and nucleus. Additionally, it was observed that the platinum deposits made blunt contacts with the plasma membrane, which suggests that the cellular influx of cisplatin is through an endocytosis-independent manner that is consistent with the passive diffusion theory of cisplatin uptake (50). 

The simplest type of membrane transport is passive diffusion of a substance across the lipid bilayer from the region of higher concentration to that of lower concentration. Many metabolites are transported across biological membranes by permeases that form pores through the membrane. The conformation of the pore is complementary to that of the substrate to be transported. Cells use energy to transport molecules across the plasma membrane against their concentration gradients, a process known as active transport. 

Figure 19.5 Central role of the plasma membrane ATPase in the maintenance of proton homeostasis within the cytoplasm. Protons gain entry into the cytoplasm through passive proton diffusion, which can increase with increasing ethanol from the uptake of protonated acids from symport with amino acids or from metabolism. The cytoplasm and vacuole can buffer proton levels, but the main buffering activity is provided by the action of the ATPase. Saturation of the ATPase can lead to cell death thus metabolic activities are tightly coordinated with ATPase activity.

Continuous pH neutralization is necessary for optimal yields in fumaric acid fermentation. At low pH, excreted fumaric acid will passively diffuse back through the plasma membrane of the fungus and decrease its intracellular pH as a result, the fermentation will fail. In addition, free fumaric acid accumulated in the medium decreases the pH, which exerts a progressive inhibitory effect on fumaric acid production. O ... 

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