Fluid secretion by the malpighian tubules of the tsetse fly Glossina morsitans: the effects of ouabain, ethacrynic acid and amiloride

1976 ◽  
Vol 65 (2) ◽  
pp. 323-332
Author(s):  
J. D. Gee
Keyword(s):  
Sodium Transport ◽  
Cardiac Glycoside ◽  
Ethacrynic Acid ◽  
Fluid Secretion ◽  
Sodium Concentration ◽  
Tsetse Fly ◽  
Malpighian Tubules ◽  
Sodium Ions ◽  
Glossina Morsitans ◽  
Sodium And Potassium

The effects of three inhibitors of sodium transport on the secretion of fluid by the Malpighian tubules of Glossina morsitans have been observed. The cardiac glycoside, ouabain, affects neither the rate of secretion nor the sodium concentration of the fluid secreted when isolated tubules are bathed by solutions containing a range of sodium and potassium concentrations. Secretion is inhibited, however, by ethacrynic acid and amiloride. The results confirm that fluid secretion by the Malpighian tubules of this insect is dependent on the active transport of sodium ions and show that Na+/k+ exchange pumps are not involved in this process.

Stimulation of sodium transport and fluid secretion by ouabain in an insect malpighian tubule

1988 ◽  
Vol 137 (1) ◽  
pp. 265-276 ◽  
Author(s):  
S. H. Maddrell ◽  
J. A. Overton
Keyword(s):  
Fluid Flow ◽  
Sodium Transport ◽  
Fluid Transport ◽  
Electrical Potential ◽  
Malpighian Tubule ◽  
Fluid Secretion ◽  
Malpighian Tubules ◽  
Sodium Ions ◽  
Tubule Cells ◽  
Stimulation Of

Ouabain, at all concentrations higher than 2 × 10(−7) mol l-1, stimulates the rate at which the Malpighian tubules of the insect, Rhodnius, transport sodium ions and fluid into the lumen. An effect on paracellular movement of sodium ions is unlikely because ouabain makes the electrical potential of the lumen more positive, which would slow diffusion of sodium into the lumen. Radioactive ouabain binds to the haemolymph-facing sides of the tubule cells but not to the luminal face. This binding is reduced in the presence of elevated levels of potassium or of non-radioactive ouabain. Bound ouabain is only slowly released on washing in ouabain-free saline. The evidence suggests that there is a Na+/K+-ATPase on the outer (serosal) membranes of the tubules. Such a pump would transport sodium in a direction opposed to the flow of ions and water involved in fluid transport; poisoning it with ouabain would remove this brake, and fluid flow and sodium transport would increase, as observed.

Active transport of sodium by the malpighian tubules of the tsetse fly Glossian morsitans

1976 ◽  
Vol 64 (2) ◽  
pp. 357-368
Author(s):  
J. D. Gee
Keyword(s):  
Cell Function ◽  
Malpighian Tubule ◽  
Active Role ◽  
Fluid Secretion ◽  
Sodium Concentration ◽  
Tsetse Fly ◽  
Malpighian Tubules ◽  
Bathing Solution ◽  
Bathing Medium

Isolated Malpighian tubules of Glossina morsitans are able to transport sodium against its concentration gradient. Their rate of secretion is dependent on the sodium concentration of the bathing medium. Potassium must be present in the bathing solution for rapid secretion to be maintained, but it does not play an active role in fluid secretion. Lithium and ammonium ions are able to substitute partially for sodium, other monovalent cations cannot. Ouabain does not affect rapid secretion by Glossina tubules in vitro. Conclusions drawn from the results are incorporated into a model of Malpighian tubule cell function in this insect.

scholarly journals Excretion in the House Cricket (Acheta Domesticus): Stimulation of Diuresis by Tissue Homogenates

1987 ◽  
Vol 129 (1) ◽  
pp. 63-81 ◽  
Author(s):  
JEFFREY H. SPRING ◽  
SHELIA R. HAZELTON
Keyword(s):  
Lethal Dose ◽  
Fluid Secretion ◽  
Sodium Concentration ◽  
Inhibitory Effect ◽  
Acheta Domesticus ◽  
Malpighian Tubules ◽  
Secretion Rate ◽  
Tissue Homogenates ◽  
Extreme Sensitivity

1. A new method is described for maintaining cricket Malpighian tubules in vitro. Warmed, oxygenated saline is circulated rapidly past the tubules, while the secreted urine is collected under oil for analysis. This technique allows the cricket tubules to be observed and manipulated for extended periods (6 h), in contrast to their short life (>1 h) using conventional methods. 2. Cricket tubules show extreme sensitivity to oxygen deprivation, such that 15 min of anoxia represents the median lethal dose (LD50) for in vitro preparations. 3. Homogenates of corpus cardiacum (CC) cause the rate of fluid secretion by the tubules to double. The maximum stimulation is dose-dependent over the range 0.01 to 1.0 CC. Homogenates of brain and other ganglia show much smaller stimulatory effects (0.01-0.02 CC-equivalents). Cyclic AMP mimics the increase in secretion rate, but has an inhibitory effect on the smooth muscle of the ureter. 4. Control preparations maintain a urine osmotic pressure (OP) that is hyperosmotic to the bath by 5–10 mosmol l−1. CC homogenate produces a decrease in urine OP to 10–12 mosmol l−1 hypo-osmotic to the bath. This suggests that active solute reabsorption is occurring in the lower tubule or ampulla. 5. Stimulation by CC homogenate increases the urine potassium concentration slightly less than two-fold, whereas the sodium concentration increases by a maximum of five-fold and remains at a higher concentration than potassium throughout the experiment. Tubule secretion rate is drastically inhibited in nominally sodium-free saline.

Excretion of ouabain by Malpighian tubules of Oncopeltus fasciatus

1984 ◽  
Vol 246 (5) ◽  
pp. R705-R715 ◽  
Author(s):  
J. Meredith ◽  
L. Moore ◽  
G. G. Scudder
Keyword(s):  
Concentration Gradient ◽  
Cardiac Glycoside ◽  
Cardiac Glycosides ◽  
Fluid Secretion ◽  
Distal Segment ◽  
Malpighian Tubules ◽  
Oncopeltus Fasciatus ◽  
Strong Concentration ◽  
Fluid Reabsorption

An in vitro preparation of Malpighian tubules was used to investigate the excretion of the polar cardiac glycoside, ouabain, in Oncopeltus fasciatus. Tubules were found to consist of at least two morphologically and physiologically distinct segments, both of which metabolized ouabain. The distal segment (segment II) secreted primary urine and ouabain. Secretion of ouabain by segment II was not observed to occur against a concentration gradient and increased with increasing fluid secretion. The proximal segment (segment I) reabsorbed fluid and ouabain but not metabolites. Ouabain was reabsorbed against a strong concentration gradient (23-fold), was independent of fluid reabsorption, and increased with increasing fluid secretion by segment II. In rapidly secreting Malpighian tubules (a situation of high cardiac glycoside secretion by segment II), the presence of segment I reduced the excretion of ouabain by 84-93%, mainly by reducing ouabain concentration. It appears excretory loss of cardiac glycosides can be reduced in O fasciatus and thus may be a factor in the sequestration of cardiac glycosides in this insect.

scholarly journals Resolution of Pump and Leak Components of Sodium and Potassium Ion Transport in Human Erythrocytes

1967 ◽  
Vol 50 (5) ◽  
pp. 1201-1220 ◽  
Author(s):  
R. L. Post ◽  
C. D. Albright ◽  
K. Dayani
Keyword(s):  
Cardiac Glycoside ◽  
Potassium Ion ◽  
Sodium Ion ◽  
The Other ◽  
Potassium Ions ◽  
Sodium Ions ◽  
Passive Transport ◽  
Potassium Ion Transport ◽  
Pump Activity ◽  
Sodium And Potassium

Further support for the pump-leak concept was obtained. Net transport was resolved into pump and leak components with the cardiac glycoside, ouabain. The specificity of ouabain as a pump inhibitor was demonstrated by its ineffectiveness when the pump was already inhibited by lack of one of the three pump substrates, sodium ion, potassium ion, or adenosine triphosphate. In the presence of ouabain the rates of passive transport of sodium and potassium ions changed almost in proportion to changes in their extracellular concentrations when one ion was exchanged for the other. In the presence of ouabain and at the extracellular concentrations which produced zero net transport, the ratio of potassium ions to sodium ions was 1.2-fold higher inside the cells than outside. This finding was attributed to a residual pump activity of less than 2% of capacity. The permeability to potassium ions was 10% greater than the permeability to sodium ions. A test was made of the independence of pump and leak. Conditions were chosen to change the rate through each pathway separately or in combination. When both pathways were active, net transport was the sum of the rates observed when each acted separately. A ratio of three sodium ions pumped outward per two potassium ions pumped inward was confirmed.

Secretion by the Malpighian Tubules of Rhodnius. The Movements of Ions and Water

1969 ◽  
Vol 51 (1) ◽  
pp. 71-97 ◽  
Author(s):  
S. H. P. MADDRELL
Keyword(s):  
Chloride Concentration ◽  
Fluid Secretion ◽  
Chloride Ions ◽  
Malpighian Tubules ◽  
Minor Role ◽  
Special Role ◽  
Sodium Ions ◽  
Bathing Medium ◽  
Rapid Flow ◽  
Bathing Fluid

1. The Malpighian tubules of Rhodnius will secrete at a normal rate in solutions containing no potassium ions and the rate is unaffected by changes in the potassium concentration, when the balance of cationic concentration is made up by sodium ions. 2. In the absence of sodium ions the rate of secretion is much reduced. The addition of very small amounts of sodium-containing solution brings about an abrupt recovery in the rate and thereafter the rate is unaffected by further increases in the sodium concentration. 3. In solutions containing either sodium or potassium with choline making up the balance of monovalent cations, the rate of fluid secretion depends linearly on the concentration of either sodium or potassium. 4. The tubules will concentrate either sodium or potassium when they are present at low concentration in the bathing fluid, even in the face of a very much larger concentration of the other cation. This suggests that there are separate mechanisms for the handling of these two ions. 5. Secretion can be supported by a solution containing ammonium ions in place of sodium and potassium. The tubules behave, at least in the short term, as if they were unable to distinguish ammonium from potassium. 6. Chloride ions appear to play a special role in that only bromide ions and, to a limited extent, nitrate ions will substitute for them. The rate of secretion depends linearly on the chloride concentration. 7. The tubules secrete a fluid which is practically iso-osmotic to the bathing fluid. The rate of secretion depends inversely on the osmolarity of the bathing fluid. The rate of movement of solute is little affected by these changes of osmolarity. It appears that water movements follow, and are closely linked with, solute movements. 8. Copper, cyanide, iodoacetate and azide ions and 2,4-dinitrophenol all stop secretion when added to the bathing medium. Ouabain, acetazolamide and mammalian ADH all have no effect on the rate of secretion and ouabain has no effect on the composition of the secreted fluid. 5-Hydroxytryptamine (serotonin) will stimulate a rapid flow of secretion. 9. Apparent neurosecretory axons have been found which supply the tubules. They do not contain enough diuretic activity to do more than play a minor role in diuresis. They may contribute to the rapid onset of diuresis or may affect the Malpighian tubules in some other way. 10. The evidence suggests that the tubules function by secreting chloride, potassium and sodium ions into the lumen (it is speculated that this may conceivably involve the active transport of all three ions) and that water movements closely follow these ion movements so that a rapid flow of iso-osmotic fluid is achieved.

Generation of transepithelial potentials by isolated perfused reptilian distal tubules

1978 ◽  
Vol 234 (3) ◽  
pp. F238-F246 ◽  
Author(s):  
K. W. Beyenbach ◽  
W. H. Dantzler
Keyword(s):  
Sodium Transport ◽  
Ethacrynic Acid ◽  
Potassium Concentration ◽  
Sodium Concentration ◽  
Garter Snake ◽  
High Sodium ◽  
Distal Tubules

Transepithelial potentials were measured in the most distal segments of garter snake (Thamnophis spp.) distal tubles perfused in vitro. The segments generated high lumen-negative potentials when sodium was in the lumen. The size of the potentials was a saturable function of luminal sodium concentrations between 0 and 32 mM. The potentials were stable with time only when sodium concentrations in the lumen were less than 30 mM. Perfusion with high sodium concentrations resulted in transient potentials. Stable potentials changed markedly when the lumen sodium concentration or the bath potassium concentration was altered suddenly, but they were independent of lumen potassium concentrations and bath sodium concentrations. Amiloride stimulated or inhibited the potentials, ouabain partially depressed them, and ethacrynic acid and cyanide inhibited them slowly and often irreversibly. We conclude that distal transepithelial potentials reflect sodium transport from lumen to bath across a tight asymmetric epithelium which differs from other sodium-transporting epithelia in that stable transepithelial potentials are maintained only with luminal sodium concentrations less than 30 mM.

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