The molecular basis of chloride transport in shark rectal gland.

1994 ◽  
Vol 196 (1) ◽  
pp. 405-418 ◽  
Author(s):  
J R Riordan ◽  
B Forbush ◽  
J W Hanrahan
Keyword(s):  
Cyclic Amp ◽  
Chloride Transport ◽  
Direct Action ◽  
Chloride Concentration ◽  
K Channel ◽  
Rectal Gland ◽  
Cl Secretion ◽  
Cl Channel ◽  
The Individual ◽  
Active Transport Process

Transepithelial Cl- secretion in vertebrates is accomplished by a secondary active transport process brought about by the coordinated activity of apical and basolateral transport proteins. The principal basolateral components are the Na+/K(+)-ATPase pump, the Na+/K+/2Cl- cotransporter (symporter) and a K+ channel. The rate-limiting apical component is a cyclic-AMP-stimulated Cl- channel. As postulated nearly two decades ago, the net Cl- movement from the blood to the lumen involves entry into the epithelial cells with Na+ and K+, followed by active Na+ extrusion via the pump and passive K+ exit via a channel. Intracellular [Cl-] is raised above electrochemical equilibrium and exits into the lumen when the apical Cl- channel opens. Cl- secretion is accompanied by a passive paracellular flow of Na+. The tubules of the rectal glands of elasmobranchs are highly specialized for secreting concentrated NaCl by this mechanism and hence have served as an excellent experimental model in which to characterize the individual steps by electrophysiological and ion flux measurements. The recent molecular cloning and heterologous expression of the apical Cl- channel and basolateral cotransporter have enabled more detailed analyses of the mechanisms and their regulation. Not surprisingly, since hormones acting through kinases control secretion, both the Cl- channel, which is the shark counterpart of the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator), and the cotransporter are regulated by phosphorylation and dephosphorylation. The primary stimulation of secretion by hormones employing cyclic AMP as second messenger activates CFTR via the direct action of protein kinase A (PKA), which phosphorylates multiple sites on the R domain. In contrast, phosphorylation of the cotransporter by as yet unidentified kinases is apparently secondary to the decrease in intracellular chloride concentration caused by anion exit through CFTR.

Cyclic AMP regulation of active chloride transport in the rectal gland of marine elasmobranchs

1977 ◽  
Vol 199 (3) ◽  
pp. 443-448 ◽  
Author(s):  
Jeffrey S. Stoff ◽  
Patricio Silva ◽  
Michael Field ◽  
John Forrest ◽  
Arthur Stevens ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Chloride Transport ◽  
Rectal Gland

Stoichiometry of sodium chloride transport by rectal gland of Squalus acanthias

1986 ◽  
Vol 250 (3) ◽  
pp. F516-F519 ◽  
Author(s):  
P. Silva ◽  
M. A. Myers
Keyword(s):  
Sodium Chloride ◽  
Chloride Transport ◽  
Chloride Concentration ◽  
Squalus Acanthias ◽  
Salt Transport ◽  
Constant Infusion ◽  
Rectal Gland ◽  
Energetic Efficiency ◽  
Plasma Sodium ◽  
Normal Concentration

The stoichiometry of the sodium chloride cotransport system was examined in isolated perfused rectal glands of Squalus acanthias by kinetic analysis of the effect on chloride secretion of progressive substitutions of other ions for sodium and chloride in the perfusate. Secretion was stimulated by a constant infusion of dibutyryl cyclic AMP (5 X 10(-5) M) and theophylline (2.5 X 10(-4) M). Sodium was replaced by N-methyl-D-glucamine, whereas chloride was replaced by gluconate. The Km values for sodium, obtained using three different graphic methods, were close to or at the normal concentration of sodium in the plasma of the shark, suggesting that plasma sodium concentration regulates transport by the gland. The Km values for chloride were far below the normal concentration of chloride in the plasma, indicating that the chloride sites are normally saturated and therefore plasma chloride concentration cannot control transport by the gland. Hill plots revealed slopes of 1.06 for sodium and 1.6 for chloride, consistent with the hypothesis that 2 Cl- and 1 Na+ interact in the cotransport process. The cotransport linkage of 2 Cl- with 1 Na+ in the initial step of entry into the cell can be viewed as a device that doubles the energetic efficiency of salt transport, allowing 2 NaCl to be secreted for every 1 Na+ actively pumped.

Hormonal regulation of active chloride transport in the dogfish rectal gland

1979 ◽  
Vol 237 (2) ◽  
pp. F138-F144 ◽  
Author(s):  
J. S. Stoff ◽  
R. Rosa ◽  
R. Hallac ◽  
P. Silva ◽  
F. H. Epstein
Keyword(s):  
Cyclic Amp ◽  
Vasoactive Intestinal Peptide ◽  
Active Transport ◽  
Hormonal Regulation ◽  
Chloride Transport ◽  
Squalus Acanthias ◽  
Rectal Gland ◽  
Electrolyte Homeostasis ◽  
Dogfish Shark

Active transport of chloride is modulated by cyclic AMP in the rectal gland of Squalus acanthias. Vasoactive intestinal peptide (VIP) specifically activates the production of cyclic AMP by the gland and stimulates the secretion of chloride. Somatostatin inhibits VIP-induced secretion but has no effect alone. Both these peptides are present in the dogfish shark and may play an important role in electrolyte homeostasis.

scholarly journals Numerical Simulation of Non-Uniformly Distributed Corrosion in Reinforced Concrete Cross-Section

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3975
Author(s):  
Magdalena German ◽  
Jerzy Pamin
Keyword(s):  
Reinforced Concrete ◽  
Cross Section ◽  
Chloride Transport ◽  
Chloride Concentration ◽  
Corrosion Current ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Initiation Phase ◽  
Chloride Corrosion ◽  
Cover Thickness

Reinforced concrete structures can be strongly damaged by chloride corrosion of reinforcement. Rust accumulated around rebars involves a volumetric expansion, causing cracking of the surrounding concrete. To simulate the corrosion progress, the initiation phase of the corrosion process is first examined, taking into account the phenomena of oxygen and chloride transport as well as the corrosion current flow. This makes it possible to estimate the mass of produced rust, whereby a corrosion level is defined. A combination of three numerical methods is used to solve the coupled problem. The example object of the research is a beam cross-section with four reinforcement bars. The proposed methodology allows one to predict evolving chloride concentration and time to reinforcement depassivation, depending on the reinforcement position and on the location of a point on the bar surface. Moreover, the dependence of the corrosion initiation time on the chloride diffusion coefficient, chloride threshold, and reinforcement cover thickness is examined.

scholarly journals A cyclic AMP-activated K+ channel in Drosophila larval muscle is persistently activated in dunce.

1991 ◽  
Vol 88 (2) ◽  
pp. 557-560 ◽  
Author(s):  
R. Delgado ◽  
P. Hidalgo ◽  
F. Diaz ◽  
R. Latorre ◽  
P. Labarca
Keyword(s):  
Cyclic Amp ◽  
K Channel ◽  
Larval Muscle

Cyclic AMP stimulates ouabain-insensitive ion movement in shark rectal gland

1984 ◽  
Vol 154 (2) ◽  
pp. 139-144 ◽  
Author(s):  
Patricio Silva ◽  
Kate Spokes ◽  
Jonathan A. Epstein ◽  
Arthur Stevens ◽  
Franklin H. Epstein
Keyword(s):  
Cyclic Amp ◽  
Rectal Gland ◽  
Ion Movement ◽  
Shark Rectal Gland

Chloride channels in apical membrane patches of stellate cells of Malpighian tubules of Aedes aegypti

2001 ◽  
Vol 204 (2) ◽  
pp. 367-378 ◽  
Author(s):  
K.R. O'Connor ◽  
K.W. Beyenbach
Keyword(s):  
Aedes Aegypti ◽  
Apical Membrane ◽  
Stellate Cells ◽  
Malpighian Tubules ◽  
Type I ◽  
Open Probability ◽  
Cl Secretion ◽  
Cl Channel ◽  
Open Time ◽  
Channel Type

Stellate cells of Aedes aegypti Malpighian tubules were investigated using patch-clamp methods to probe the route of transepithelial Cl(−) secretion. Two types of Cl(−) channel were identified in excised, inside-out apical membrane patches. The first Cl(−) channel, type I, had a conductance of 24 pS, an open probability of 0.816+/−0.067, an open time of 867+/−114 ms (mean +/− s.e.m., four patches) and the selectivity sequence I(−)>Cl(−)(much greater than) isethionate>gluconate. The I(−)/Cl(−)>>isethionate>gluconate. The I(−)Cl(−) permeability ratio was 1.48, corresponding to Eisenman sequence I. The type I Cl(−) channel was blocked by 2,2′-iminodibenzoic acid (DPC) and niflumic acid (2-[3-(trifluoromethyl)anilo]nicotinic acid). The removal of Ca(2+) from the Ringer's solution on the cytoplasmic side had no effect on channel activity. The second Cl(−) channel, type II, had a conductance of 8 pS, an open probability of 0.066+/−0.021 and an open time of 7.53+/−1.46 ms (mean +/− s.e.m., four patches). The high density and halide selectivity sequence of the type I Cl(−) channel is consistent with a role in transepithelial Cl(−) secretion under control conditions, but it remains to be determined whether these Cl(−) channels also mediate transepithelial Cl(−) secretion under diuretic conditions in the presence of leucokinin.

scholarly journals Effect of ATP-sensitive K+ channel regulators on cystic fibrosis transmembrane conductance regulator chloride currents.

1992 ◽  
Vol 100 (4) ◽  
pp. 573-591 ◽  
Author(s):  
D N Sheppard ◽  
M J Welsh
Keyword(s):  
Cystic Fibrosis ◽  
Voltage Dependence ◽  
K Channel ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
K Channels ◽  
Intracellular Atp ◽  
Cl Channel ◽  
Cl Channels ◽  
Cystic Fibrosis Transmembrane

The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl- channel that is regulated by cAMP-dependent phosphorylation and by intracellular ATP. Intracellular ATP also regulates a class of K+ channels that have a distinct pharmacology: they are inhibited by sulfonylureas and activated by a novel class of drugs called K+ channel openers. In search of modulators of CFTR Cl- channels, we examined the effect of sulfonylureas and K+ channel openers on CFTR Cl- currents in cells expressing recombinant CFTR. The sulfonylureas, tolbutamide and glibenclamide, inhibited whole-cell CFTR Cl- currents at half-maximal concentrations of approximately 150 and 20 microM, respectively. Inhibition by both agents showed little voltage dependence and developed slowly; > 90% inhibition occurred 3 min after adding 1 mM tolbutamide or 100 microM glibenclamide. The effect of tolbutamide was reversible, while that of glibenclamide was not. In contrast to their activating effect on K+ channels, the K+ channel openers, diazoxide, BRL 38227, and minoxidil sulfate inhibited CFTR Cl- currents. Half-maximal inhibition was observed at approximately 250 microM diazoxide, 50 microM BRL 38227, and 40 microM minoxidil sulfate. The rank order of potency for inhibition of CFTR Cl- currents was: glibenclamide < BRL 38227 approximately equal to minoxidil sulfate > tolbutamide > diazoxide. Site-directed mutations of CFTR in the first membrane-spanning domain and second nucleotide-binding domain did not affect glibenclamide inhibition of CFTR Cl- currents. However, when part of the R domain was deleted, glibenclamide inhibition showed significant voltage dependence. These agents, especially glibenclamide, which was the most potent, may be of value in identifying CFTR Cl- channels. They or related analogues might also prove to be of value in treating diseases such as diarrhea, which may involve increased activity of the CFTR Cl- channel.

scholarly journals THE TUMOR-PROMOTER PHORBOL ESTER (12-0-TETRADECANOYL-PHORBOL-13-ACETATE), A POTENT AGGREGATING AGENT FOR BLOOD PLATELETS

1974 ◽  
Vol 60 (2) ◽  
pp. 325-336 ◽  
Author(s):  
Marjorie B. Zucker ◽  
Walter Troll ◽  
Sidney Belman
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Phorbol Ester ◽  
Platelet Rich Plasma ◽  
Direct Action ◽  
Blood Platelets ◽  
Tumor Promoter ◽  
Metabolic Inhibitors ◽  
Rapid Phase ◽  
Low Concentrations

The phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate, a potent tumor-promoting agent, caused irreversible platelet aggregation when more than 0.02 µM was stirred with human citrated or heparinized platelet-rich plasma (PRP). With washed platelets, 1 nM was effective. The alcohol phorbol, which has little tumor-promoting activity, failed to cause platelet aggregation. With all but low concentrations of phorbol ester, aggregation was succeeded by a rapid phase. The latter was prevented or reduced by enzymes which destroy ADP and by aspirin, was associated with a change in platelet shape, and was presumably due to released ADP. At higher concentrations, only a rapid phase was seen, and these inhibitors were not effective. Low concentrations did not aggregate platelets in PRP containing sufficient EDTA or EGTA to chelate ionized calcium or in PRP from thrombasthenic patients; higher concentrations caused slight aggregation. Both the primary, non-ADP-dependent aggregation and the rapid ADP-dependent aggregation were markedly inhibited by substances which increase cyclic AMP, metabolic inhibitors, and the sulfhydryl inhibitor N-ethylmaleimide. Phorbol ester reduced platelet cyclic AMP only when it had been previously elevated by prostaglandin E1. 1 µM did not release ß-glucuronidase, lactic dehydrogenase, or inflammatory material from platelets in 4–5 min despite marked aggregation, but liberated all three in 30 min. The possibility is discussed that low phorbol ester concentrations cause primary aggregation by a direct action on platelet actomyosin.

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