On the structural organization of biological pumps and channels

1984 ◽  
Vol 42 ◽  
pp. 138-141
Author(s):  
G. Zampighi ◽  
M. Kreman
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Plasma Membranes ◽  
Transport Proteins ◽  
Molecular Organization ◽  
Passive Transport ◽  
Concentration Gradients ◽  
Cell Functions ◽  
Natural Concentration ◽  
Active Transport System

The plasma membranes of most animal cells contain transport proteins which function to provide passageways for the transported species across essentially impermeable lipid bilayers. The channel is a passive transport system which allows the movement of ions and low molecular weight molecules along their concentration gradients. The pump is an active transport system and can translocate cations against their natural concentration gradients. The actions and interplay of these two kinds of transport proteins control crucial cell functions such as active transport, excitability and cell communication. In this paper, we will describe and compare several features of the molecular organization of pumps and channels. As an example of an active transport system, we will discuss the structure of the sodium and potassium ion-activated triphosphatase [(Na+ +K+)-ATPase] and as an example of a passive transport system, the communicating channel of gap junctions and lens junctions.

Selectivity Mechanisms of Sethoxydim Absorption into Tissues of Corn (Zea mays) and Pea (Pisum sativum)

Weed Science ◽  
1987 ◽  
Vol 35 (5) ◽  
pp. 619-622 ◽  
Author(s):  
Hideo Hosaka ◽  
Masae (Kubota) Takagi
Keyword(s):  
Zea Mays ◽  
Pisum Sativum ◽  
Active Transport ◽  
Transport System ◽  
Hydroponic Culture ◽  
Passive Transport ◽  
Tolerant Plants ◽  
Active Transport System

The selectivity mechanisms of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were investigated by examining absorption of14C-sethoxydim into tissues of corn (Zea maysL. ‘Goldencrossbantam′) and pea (Pisum sativumL. ‘Alaska′). Greater absorption of14C-sethoxydim was observed only into the proliferative 2-mm terminals of the excised roots of susceptible corn, and the same result was obtained with corn seedlings in hydroponic culture. Absorption was not affected by 1 × 10−4M 2,4-dinitrophenol (DNP), which indicated that the absorption of14C-sethoxydim is probably mediated by a passive transport system rather than an active transport system. The selective herbicidal action of sethoxydim appeared to depend largely on the differential rates of absorption into meristematic regions by the susceptible and tolerant plants.

scholarly journals Actions of external hypertonic urea, ADH, and theophylline on transcellular and extracellular solute permeabilities in frog skin.

1975 ◽  
Vol 65 (5) ◽  
pp. 599-615 ◽  
Author(s):  
L J Mandel
Keyword(s):  
Linear Relationship ◽  
Active Transport ◽  
Transport System ◽  
Frog Skin ◽  
Open Circuit Potential ◽  
Open Circuit ◽  
Solute Permeability ◽  
Parallel Lines ◽  
Paracellular Pathways ◽  
Active Transport System

Increases in transepithelial solute permeability were elicited in the frog skin with external hypertonic urea, theophylline, and vasopressin (ADH). In external hypertonic urea, which is known to increase the permeability of the extracellular (paracellular) pathway, the unidirectional transepithelial fluxes of Na (passive), K, Cl, and urea increased substantially while preserving a linear relationship to each other. The same linear relationship was also observed for the passive Na and urea fluxes in regular Ringer and under stimulation with ADH or 10 mM theophylline, indicating that their permeation pathway was extracellular. A linear relationship between Cl and urea fluxes could be demonstrated if the skins were separated according to their open circuit potentials; parallel lines were obtained with increasing intercepts on the Cl axis as the open circuit potential decreased. The slopes of the Cl vs. urea lines were not different from that obtained in external hypertonic urea, indicating that this relationship described the extracellular movement of Cl. The intercept on the ordinate was interpreted as the contribution from the transcellular Cl movement. In the presence of 0.5 mM theophylline or 10 mU/ml of ADH, mainly the transcellular movement of Cl increased, whereas 10 mM theophylline caused increases in both transcellular and extracellular Cl fluxes. These and other data were interpreted in terms of a possible intracellular control of the theophylline-induced increase in extracellular fluxes. The changes in passive solute permeability were shown to be independent of active transport. The responses of the active transport system, the transcellular and paracellular pathways to theophylline and ADH could be explained in terms of the different resulting concentrations of cyclic 3'-5'-AMP produced by each of these substances in the tissue.

A linked active transport system for Na+ and K+ in a glial cell line

1976 ◽  
Vol 104 (1) ◽  
pp. 93-105 ◽  
Author(s):  
Gary Kukes ◽  
Jean De Vellis ◽  
Rafael Elul
Keyword(s):  
Cell Line ◽  
Glial Cell ◽  
Active Transport ◽  
Transport System ◽  
Active Transport System

The pH-dependent uptake of putrescine by Pseudomonas acidovorans and its incorporation into bacteriophage DNA

1983 ◽  
Vol 29 (7) ◽  
pp. 827-829 ◽  
Author(s):  
D. L. Bruce ◽  
R. A. J. Warren
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Normal Condition ◽  
Intracellular Pool ◽  
Pseudomonas Acidovorans ◽  
Ph Dependent ◽  
Active Transport System

Lack of an active transport system prevents Pseudomonas acidovorans taking up putrescine under normal condition of growth. At pH 9.5, however, putrescine does enter the cell. That putrescine enters the intracellular pool is shown by its conversion to 2-hydroxyputrescine and spermidine after the cells are returned to pH 7.0. The accumulated putrescine can be used to label specifically the α-putrescinylthymine residues of bacteriophage [Formula: see text] DNA.

Participation of an active transport system in berberine-secreting cultured cells of Thalictrum minus

1987 ◽  
Vol 6 (5) ◽  
pp. 356-359 ◽  
Author(s):  
H. Yamamoto ◽  
M. Suzuki ◽  
Y. Suga ◽  
H. Fukui ◽  
M. Tabata
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Cultured Cells ◽  
Thalictrum Minus ◽  
Active Transport System

scholarly journals The Active Transport of Sodium by Ghosts of Human Red Blood Cells

1962 ◽  
Vol 45 (5) ◽  
pp. 837-859 ◽  
Author(s):  
Joseph F. Hoffman
Keyword(s):  
Active Transport ◽  
Blood Cells ◽  
Total Population ◽  
Passive Transport ◽  
Intact Cells ◽  
Exchange Diffusion ◽  
Human Red Blood Cells ◽  
Hypotonic Hemolysis ◽  
Active Transport System ◽  
External K

The outflux of Na24 from prelabeled ghosts was measured under various conditions. Prelabeling was accomplished by hypotonic hemolysis of intact human cells in the presence of tracer Na24. The resultant ghosts when subsequently washed were found to retain 10 to 20 per cent of the initial Na24. Separate experiments indicated that this trapped amount resides in only a portion of ghosts comprising the total population. The characteristics of the outflux of this residual Na24 indicated that the ghost system closely resembles intact red cells. The outflux of Na from ghosts could be divided into three components: active and passive transport and exchange diffusion. The active transport system, necessarily driven by metabolism, required the presence of K in the extracellular phase and was blocked by strophanthidin. The concentration dependence of the Na pump flux on the external K and internal Na appeared the same in ghosts as in intact cells. Certain other features of this ghost system are also discussed.

Reconstitution of an ATP-mediated Active Transport System across Black Lipid Membranes

Nature ◽  
1969 ◽  
Vol 222 (5196) ◽  
pp. 871-872 ◽  
Author(s):  
MAHENDRA K. JAIN ◽  
ALFRED STRICKHOLM ◽  
E. H. CORDES
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Lipid Membranes ◽  
Black Lipid Membranes ◽  
Active Transport System
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