Effects of dinitrophenol on active-transport processes and cell membranes in the Malpighian tubule of Formica

1994 ◽  
Vol 428 (2) ◽  
pp. 150-156 ◽  
Author(s):  
S. Dijkstra ◽  
E. Lohrmann ◽  
E. Van Kerkhove ◽  
P. Steels ◽  
R. Greger
Keyword(s):  
Active Transport ◽  
Cell Membranes ◽  
Malpighian Tubule ◽  
Transport Processes

scholarly journals The Transport of Salt and Water across Isolated Rat Ileum

1967 ◽  
Vol 50 (3) ◽  
pp. 695-727 ◽  
Author(s):  
T. W. Clarkson
Keyword(s):  
Active Transport ◽  
Transport Processes ◽  
Irreversible Processes ◽  
Pressure Gradients ◽  
Ion Flow ◽  
Chemical Gradients ◽  
In Series ◽  
Frictional Coefficients ◽  
The Relationship ◽  
Active Channel

The flows of sodium, potassium, and chloride under electrical and chemical gradients and of salt and water in the presence of osmotic pressure gradients are described by phenomenological equations based on the thermodynamics of irreversible processes. The aim was to give the simplest possible description, that is to postulate the least number of active transport processes and the least number of separate pathways across the intestine. On this basis, the results were consistent with the following picture of the intestine: Two channels exist across this tissue, one allowing only passive transport of ions and the other only active. In the passive channel, the predominant resistance to ion flow is friction with the water in the channel. The electroosmotic flow indicates that the passive channel is lined with negative fixed charged groups having a surface charge density of 3000 esu cm-2. The values of the ion-water frictional coefficients, and the relationship between ionic concentrations and flows indicate that the passive channel is extracellular. The active channel behaves as two membranes in series, the first membrane being semipermeable but allowing active transport of sodium, and the second membrane being similar to the passive channel. Friction with the ions in the second "membrane" is the predominant resistance to water flow.

scholarly journals AMP-Activated Protein Kinase (AMPK)-Dependent Regulation of Renal Transport

2018 ◽  
Vol 19 (11) ◽  
pp. 3481 ◽  
Author(s):  
Philipp Glosse ◽  
Michael Föller
Keyword(s):  
Membrane Transport ◽  
Active Transport ◽  
Collecting Duct ◽  
Distal Tubule ◽  
Transport Processes ◽  
Acid Oxidation ◽  
Serine Threonine Kinase ◽  
Energy Deficiency ◽  
Energy Consuming ◽  
Amp Activated Protein Kinase

AMP-activated kinase (AMPK) is a serine/threonine kinase that is expressed in most cells and activated by a high cellular AMP/ATP ratio (indicating energy deficiency) or by Ca2+. In general, AMPK turns on energy-generating pathways (e.g., glucose uptake, glycolysis, fatty acid oxidation) and stops energy-consuming processes (e.g., lipogenesis, glycogenesis), thereby helping cells survive low energy states. The functional element of the kidney, the nephron, consists of the glomerulus, where the primary urine is filtered, and the proximal tubule, Henle’s loop, the distal tubule, and the collecting duct. In the tubular system of the kidney, the composition of primary urine is modified by the reabsorption and secretion of ions and molecules to yield final excreted urine. The underlying membrane transport processes are mainly energy-consuming (active transport) and in some cases passive. Since active transport accounts for a large part of the cell’s ATP demands, it is an important target for AMPK. Here, we review the AMPK-dependent regulation of membrane transport along nephron segments and discuss physiological and pathophysiological implications.

Ion and water distribution in pig lenses incubated at 0 °C to disable ion transport pumps

1991 ◽  
Vol 69 (10-11) ◽  
pp. 742-746 ◽  
Author(s):  
Ivan L. Cameron ◽  
W. Elaine Hardman ◽  
Gary D. Fullerton ◽  
Miklos Kellermayer ◽  
Andrea Ludany ◽  
...  
Keyword(s):  
Water Content ◽  
Active Transport ◽  
Water Distribution ◽  
Content Volume ◽  
Cell Volume Regulation ◽  
Transport Processes ◽  
Water Volume ◽  
Bathing Solution ◽  
Ion Distribution ◽  
Lens Cell

This study was designed to test how extended exposure of lenses to sera with different ionic strengths influences the distribution of ions and water in the lens. Pig lenses were incubated in cold sera (0 °C), which were adjusted to variable concentrations of NaCl, and their K+, Na+, Cl−, and water contents were measured. Incubation at 0 °C inhibits active transport processes and thereby allows equilibration of the mobile ions and water. The hypothesis was that lens water content (volume) would follow the ion-induced protein changes predicted by a model derived from previous osmotic studies on proteins. As expected, exposure of the lens to cold caused a gain of sodium and a partial loss of potassium. However, the potassium concentration in the lens remained several fold higher than that in the bathing solution (about 41 vs. 1.8–4.6 mM/kg H2O), indicating that a portion of the potassium within the cold-exposed lens was not free to diffuse. That the water content of the lens showed a negative rather than a positive relationship with the concentration of NaCl within the lens was explained by the idea that an increase in NaCl within the lens (up to at least 250 mM/kg H2O) causes a decrease in the osmotically unresponsive water volume associated with lens proteins.Key words: pig lens, cell water, Na+, K+, Cl−, osmotic pressure, ion distribution, cell volume regulation, inhibition of active transport.

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