Effect of loop diuretics on bullfrog cornea epithelium

1989 ◽  
Vol 256 (4) ◽  
pp. C750-C755 ◽  
Author(s):  
W. Nagel ◽  
G. Carrasquer
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Loop Diuretics ◽  
Cl Transport ◽  
Before And After ◽  
The Difference ◽  
Cornea Epithelium

The effect of loop diuretics on Cl transport was studied on an in vitro preparation of the bullfrog cornea. Bumetanide (10(-4) M) or furosemide (10(-3) M) added to the stromal solution decreased Cl transport measured as the short-circuit current (Isc) to values near zero. Concomitantly, transepithelial conductance (gt) decreased, whereas the intracellular potential (Vo) hyperpolarized and the fractional resistance of the apical membrane (fRo) increased. Substitution of SO4 for Cl in the tear-side solution led to prompt changes in Isc, gt, Vo, and fRo, characteristic of appreciable passive Cl movement across the apical membrane before and after inhibition. Epinephrine (10(-4) M) was similarly effective on apical membrane conductance in inhibited tissues as under control conditions, but the effective electromotive force for transepithelial Cl transport was reduced to approximately 25%. Intracellular Cl activity, measured with ion-selective microelectrodes, decreased so much that the difference in electrochemical Cl potential divided by the Faraday constant (delta mu Cl/F) was close to zero after inhibition of Isc by bumetanide. Apical Cl permeability remained essentially unchanged. Accordingly, loop diuretics inhibit Cl transport in the Cl-secreting cornea epithelium by blocking the Na-Cl symport without secondary apical effects, as believed for other Cl-reabsorbing epithelia.

Insulin action on electrophysiological properties of apical and basolateral membranes of frog skin

1987 ◽  
Vol 252 (4) ◽  
pp. C411-C417 ◽  
Author(s):  
H. F. Schoen ◽  
D. Erlij
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Electrophysiological Properties ◽  
Basolateral Membranes ◽  
Control Value ◽  
Intracellular Na Activity ◽  
Before And After

We measured the effects of insulin on the current-voltage (I-V) relations of frog skins impaled with an intracellular microelectrode. The current across the cell membranes was assumed to be equal to the amiloride-inhibitable current. Insulin increased short-circuit current (Isc) approximately 40% from the control value. The increase in Isc was associated with a depolarization of the cell membrane. In addition there was an increase in the value of the parameters that describe the ease of movement of Na+ across the apical membrane, namely, slope conductance (ga), chord conductance (Ga), and permeability (PNa). The values of these parameters show remarkable linear correlations with membrane current both before and after stimulation. Intracellular Na+ activity (acNa) was determined from the I-V relations of the apical membrane. Insulin did not significantly modify acNa. Insulin also increased the value of the basolateral membrane conductance, however, the relationship between this parameter and current was complex. These experiments show that the stimulatory effect of insulin on Isc is associated with an increase in the conductance of both the apical and basolateral membranes.

scholarly journals Temperature Acclimation of Intestinal Na Transport in the Carp (Cyprinus Carpio L.)

1985 ◽  
Vol 114 (1) ◽  
pp. 355-364
Author(s):  
J. S. Gibson ◽  
J. C. Ellory ◽  
A. R. Cossins
Keyword(s):  
Low Temperature ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Temperature Acclimation ◽  
Na Transport ◽  
Carp Cyprinus Carpio ◽  
The Difference

1. Carp intestine mounted in vitro has a positive serosal potential and a net Na absorption greater than the short-circuit current. 2. At 30°C in vitro, tissues from 10°C-acclimated fish are thought to show heat-damage. 3. When measured at 10°C in vitro, intestine from fish acclimated to 10°C shows a greater rate of sodium transport than that from 30°Cacclimated fish. 4. Mucosal application of amphotericin B, at 10°C in vitro, increases short-circuit current and net Na flux in both 10°C- and 30°C-acclimated fish but does not diminish the difference in Na transport between the two groups, under conditions when the apical membrane permeability is not limiting. 5. It is concluded that the principal acclimatization in carp intestine to low temperature is via an increased basolateral membrane Na pumping capacity.

Na and Cl Transport across the Isolated Anterior Intestine of the Plaice Pleuronectes Platessa

1981 ◽  
Vol 90 (1) ◽  
pp. 123-142
Author(s):  
M. M. P. RAMOS ◽  
J. C. ELLORY
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Negative Potential ◽  
Loop Diuretics ◽  
Significant Part ◽  
Cl Transport ◽  
Anterior Intestine ◽  
Short Circuit Currents ◽  
Na Uptake

1. The tissue was found to have a serosa negative potential, and short-circuit currents equivalent to the net Cl transport. 2. A significant part of the Cl uptake was Na dependent and a similar fraction of the Na uptake was Cl dependent. 3. Short-circuit current and uptake of both ions were inhibited by loop diuretics and analogues. 4. I80 and P.D. were abolished by ouabain. 5. The observations are consistent with the idea of a coupled NaCl entry into the cell, using the energy inherent in the Na gradient; Na being pumped out of the cells by the Na pump and followed electrically by Cl−. Net chloride transport and the serosa negative potential would be a consequence of the permselective properties of the junctions allowing Na but not Cl to recycle back to the mucosal solution.

Role of alpha 1- and alpha 2-adrenergic receptors in Cl- transport across frog corneal epithelium

1988 ◽  
Vol 255 (6) ◽  
pp. C724-C730 ◽  
Author(s):  
T. C. Chu ◽  
O. A. Candia
Keyword(s):  
Adenylate Cyclase ◽  
Corneal Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Negative Influence ◽  
Adenylate Cyclase System ◽  
Positive Effects ◽  
Cl Transport ◽  
Beta Agonists

Norepinephrine, 10(-6) M, reduced Cl- transport by 26% in 75% of isolated frog corneal epithelia. This inhibition was not previously reported. Since beta-adrenergic agonists are known to only stimulate Cl- transport, the action of specific alpha 1- and alpha 2-agonists on Cl- transport and electrical parameters was investigated. Phenylephrine, an alpha 1-agonist always stimulated the Cl(-)-dependent short-circuit current (Isc), but less than the beta-agonists. UK-14,304-18 (UK), a selective alpha 2-agonist, reduced both the Isc (by 31% at 10(-5) M) and the stroma-to-tear unidirectional Cl- flux. UK hyperpolarized the apical membrane potential difference and increased the transepithelial resistance and apical-to-basolateral resistance ratio. UK reduced forskolin-stimulated adenylate cyclase activity by 36%. The electrophysiological effects of UK are consistent with a reduction of the Cl- permeability at the apical membrane. Pretreatment with UK sensitized the tissue for a greater effect by forskolin. Results show that the frog corneal epithelium also possesses alpha 1- and alpha 2-receptors, the latter negatively coupled to the adenylate cyclase system. Cl- transport is thus regulated by an interaction between the positive effects of beta- and alpha 1-stimulation and the negative influence of alpha 2-stimulation.

Electron probe X-ray microanalysis of the effects of Bacillus thuringiensis var kurstaki crystal protein insecticide on ions in an electrogenic K+-transporting epithelium of the larval midgut in the lepidopteran, Manduca sexta, in vitro

1985 ◽  
Vol 74 (1) ◽  
pp. 137-152
Author(s):  
B.L. Gupta ◽  
J.A. Dow ◽  
T.A. Hall ◽  
W.R. Harvey
Keyword(s):  
Bacillus Thuringiensis ◽  
Manduca Sexta ◽  
Goblet Cell ◽  
Electron Probe ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
X Ray ◽  
Elemental Concentrations

An alkaline hydrolysate of Bacillus thuringiensis var kurstaki HD1 (Btk) parasporal crystals was administered at 25 micrograms ml-1 (f.c.) to isolated, short-circuited, midguts of tobacco hornworm (Manduca sexta) larvae. The short-circuit current (s.c.c.), a precise measure of K+ active transport, was inhibited by 78% in 10 min in Btk-treated midguts as compared to controls. The elemental concentrations of K, together with Na, Mg, P, S, Cl and Ca, as well as the water content, were determined by electron probe X-ray microanalysis (EPXMA) in the muscle cells, columnar cells and goblet cells, as well as in the extracellular goblet cavity and the bathing media. The average K concentration in the goblet cell cavity was 129 mmol/kg wet wt in control midguts but only 37 mmol/kg wet wt in Btk-treated midguts. The elemental concentrations, including that of K, in other cell compartments were much less affected by Btk, but a rise in total cell calcium is suggested. It has been previously suggested that in vitro Btk acts specifically on limited regions of the apical membrane of the midgut epithelial cells. The simplest interpretation of the EPXMA results would be that initially Btk interacts specifically with the goblet cell apical membrane, which bounds the goblet cavity and contains the K+ pump responsible for the s.c.c. and high transepithelial potential difference (p.d.). Such interaction results in a rapid disruption of K+ transport across the goblet cell apical membrane, leading to dissipation of the K+ gradient and loss of p.d. The histopathological changes previously reported by other workers would then be a consequence of K+ pump inhibition causing changes in the intracellular pH, Ca2+ etc. Some possible molecular bases for these specific interactions between Btk and cell membrane are discussed.

Apical nonspecific cation conductances in rabbit cecum

1994 ◽  
Vol 266 (3) ◽  
pp. G475-G484 ◽  
Author(s):  
J. H. Sellin ◽  
W. P. Dubinsky
Keyword(s):  
Epithelial Transport ◽  
Apical Membrane ◽  
Divalent Cations ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Na Channel ◽  
Similar Response ◽  
Electrogenic Transport

Rabbit cecum exhibits electrogenic Na absorption in vitro. However, because this transport process is not inhibited by amiloride nor does it demonstrate saturation kinetics typical of the amiloride-inhibitable Na channel, we considered whether the cecal transporter represented one of a recently described family of nonselective cation conductances or channels (NSCC). Both transepithelial and vesicle studies demonstrated that K, Cs, and Rb were transported via an apical conductance. Electrogenic transport was inhibited by divalent cations including Ca, Mg, and Ba but was unaffected by either lanthanum or gadolinium. Parallel studies in distal colon did not exhibit a similar response to either K substitution or Ba inhibition. Phenamil, verapamil, and nicardipine significantly inhibited the short-circuit current (Isc). stimulated by nominal Ca- and Mg-free conditions. Flux studies demonstrated a correlation between changes in Isc and Na transport. Microelectrode impalement studies suggested that there may be both NSCC and K conductance in the apical membrane. Planar bilayer studies identified a 190-pS cation channel that may correlate with the macroscopic transport properties of this epithelium. These studies are consistent with a model of cecal Na absorption mediated by a NSCC in the apical membrane; this may be the mechanism underlying the distinct epithelial transport characteristics of this intestinal segment.

scholarly journals Transport Properties of Locust Ileum in vitro: Effects of Cyclic Amp

1988 ◽  
Vol 137 (1) ◽  
pp. 361-385 ◽  
Author(s):  
B. Irvine ◽  
N. Audsley ◽  
R. Lechleitner ◽  
J. Meredith ◽  
B. Thomson ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Active Absorption ◽  
Rate Of Absorption ◽  
The Difference ◽  
In Vitro Effects ◽  
Resistance Decrease

1. Short-circuited locust ilea exhibited electrical properties remarkably similar to those of recta. The large short-circuit current (Isc) and transepithelial potential, both indicating net active absorption of anions, initially began to decline to zero but could be fully restored by adding cyclic AMP or extracts of corpus cardiacum and ventral abdominal ganglia to the haemocoel side. 2. Ion substitutions and radiotracer flux studies indicated that cyclic AMP-induced ΔIsc was due to electrogenic Cl− transport with kinetics identical to those of the rectum. Concurrent decreases in transileal resistance were due to increases in both Cl− and K+ (PK) permeabilities, most evident as a resistance decrease at the apical membrane. The ΔPK was blocked by basolateral addition of Ba2+, as observed for recta. 3. Everted ileal sacs under open-circuit conditions absorbed a slightly hyperosmotic NaCl-rich fluid and the rate of absorption was increased more than twofold by cyclic AMP. This contrasts with stimulated recta which absorb primarily KCl and a hyposmotic absorbate. Flux studies with short-circuited ilea demonstrated active absorption of Na+ (JnetNa), which was stimulated twofold by cyclic AMP. Removal of external Na+ had little effect on Isc, suggesting that JnetNa involves exchange for another cation, e.g. NH4+. 4. Ilea actively secreted acid at lower rates than do recta under open-circuit conditions. Under short-circuit conditions, cyclic AMP addition led to active alkalinization of the ileal lumen at high rates, and the large Isc represented the difference between active secretion of base equivalents and net absorption of Cl−. 5. The transport capacities of locust ilea and recta are compared in relation to their ultrastructure.

L-glutamine with D-glucose stimulates oxidative metabolism and NaCl absorption in piglet jejunum

1992 ◽  
Vol 263 (6) ◽  
pp. G960-G966 ◽  
Author(s):  
J. M. Rhoads ◽  
E. O. Keku ◽  
J. P. Woodard ◽  
S. I. Bangdiwala ◽  
J. G. Lecce ◽  
...  
Keyword(s):  
Oxidative Metabolism ◽  
Carbonic Acid ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Glutamine Metabolism ◽  
Nacl Absorption ◽  
The Relationship ◽  
Stimulation Of

To explore the relationship between intestinal fluid absorption and oxidative metabolism, we measured the effects of amino acids and glucose on piglet jejunal ion transport and oxygen consumption (QO2) in vitro. Jejunal QO2 was stimulated by L-glutamine and D-glucose but not by the nonmetabolizable organic solutes methyl beta-D-glucoside or L-phenylalanine. QO2 was maximally enhanced by the combination of D-glucose and L-glutamine (5 mM). Even though 5 mM L-glutamine was previously found to be insufficient to stimulate NaCl absorption, 5 mM L-glutamine enhanced jejunal NaCl flux when combined with equimolar mucosal D-glucose. Either D-glucose or methyl beta-D-glucoside caused an increase in short-circuit current (Isc), an increase in Na+ absorption in excess of Isc, and a decrease in Cl- secretion, when L-glutamine was substituted for D-glucose (10 mM) on the serosal side. This relationship suggests that mucosal sugars, if combined with L-glutamine, enhance neutral NaCl absorption as well as electrogenic Na+ flow. (Aminooxy)acetate, an inhibitor of alanine aminotransferase, abolished the stimulation of QO2 and the NaCl-absorptive response to L-glutamine. We conclude that the oxidative metabolism fueled by L-glutamine is linked to a NaCl-absorptive mechanism in the intestine. We propose that the CO2 produced by glutamine metabolism yields carbonic acid, which dissociates to H+ and HCO3-, which may stimulate parallel antiports in the apical membrane.

Diluting segment in kidney of dogfish shark. II. Electrophysiology of apical membranes and cellular resistances

1990 ◽  
Vol 258 (2) ◽  
pp. R409-R417 ◽  
Author(s):  
S. C. Hebert ◽  
P. A. Friedman
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Membrane Voltage ◽  
Primary Resistance ◽  
Diluting Segment ◽  
Dogfish Shark

Diluting segments from the bundle zone of the dogfish shark kidney were perfused in vitro and the electrophysiological characteristics of this segment investigated using conventional microelectrodes and cable analysis. In 21 tubules perfused with symmetrical Ringer solutions the average transepithelial voltage (Vte), transepithelial conductance (Gte), and equivalent short circuit current (Isc) were 8.7 +/- 0.6 mV, 91.3 +/- 10.2 mS/cm2, and 641 +/- 48 microA/cm2, respectively. Microelectrode impalements in 52 cells yielded values for the basolateral membrane voltage (Vb) and an estimated apical membrane fractional resistance (fRa) of -57.5 +/- 1.3 mV and 0.896 +/- 0.008, respectively. All of these parameters were distributed in a Gaussian manner. Liminal furosemide (10(-4) M) abolished Isc, hyperpolarized apical membrane voltage (Va) and Vb, increased Gte, and reduced fRa. The apical membrane was predominantly conductive to K+: increasing luminal K+ from 5 to 49.7 mM resulted in an apical depolarization of 41.2 mV and a fall in fRa and luminal Ba2+ (1 mM) depolarized Va by 14.3 mV and increased fRa. The apical transference number for K+ was 0.74 +/- 0.07. The cellular and paracellular resistances were estimated from the effects of luminal Ba2+ on fRa and Gte. The cell conductance represented approximately 45% of Gte, with the primary resistance barrier located at the apical membrane: apical membrane resistance was 59.7 +/- 16.0 and basolateral membrane resistance was 5.9 +/- 2.3 omega.cm2. From these resistance values together with the passive permeability (PNa/PCl) of 2.5 determined previously, the ratio of net Cl- absorption to net transcellular Na+ absorption was determined to be 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of "loop" diuretics on ion transport by dog tracheal epithelium

1983 ◽  
Vol 245 (5) ◽  
pp. C388-C396 ◽  
Author(s):  
J. H. Widdicombe ◽  
I. T. Nathanson ◽  
E. Highland
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Loop Diuretics ◽  
Tracheal Epithelium ◽  
Isolated Cells ◽  
Significant Fall ◽  
Cl Transport ◽  
Site Of Action ◽  
Net Flux

The "loop" diuretics MK-196, bumetanide, piretanide, and furosemide are all potent inhibitors of Cl transport by the dog's tracheal epithelium. In short-circuited tissues, the drugs caused significant decreases in both unidirectional Cl fluxes and in the net flux of Cl toward the lumen; the change in net Cl flux was not significantly different from the change in short-circuit current. The drugs had no effect on active Na absorption. All drugs caused a significant fall in tissue conductance. All drugs, except MK-196, were more potent from the serosal bath; MK-196 was equipotent from either side of the tissue. In experiments with isolated cells, the diuretics caused no significant changes in intracellular Na and K concentrations, a fall in intracellular Cl concentration, and approximately equal falls in Na and Cl influxes. These results suggest that the site of action of these drugs is on a basolateral linked Na-Cl entry process. Additional evidence for such a linked entry process was provided by experiments in which removal of Cl reduced Na influx and removal of Na reduced Cl influx.

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