Active Transport of Magnesium by the Malpighian Tubules of the Larvae of the Mosquito, Aedes Campestris

1974 ◽  
Vol 61 (3) ◽  
pp. 761-771
Author(s):  
J. E. PHILLIPS ◽  
S. H. P. MADDRELL
Keyword(s):  
Active Transport ◽  
Concentration Gradient ◽  
Fluid Transport ◽  
Electrical Potential ◽  
Malpighian Tubules ◽  
Mosquito Larvae ◽  
Electrical Potential Difference ◽  
Maximal Rate ◽  
Magnesium Ions ◽  
Saturation Kinetics

1. Larvae of Aedes campestris can survive in water containing up to 100 mM Mg even though they ingest and absorb into the haemolymph considerable amounts of magnesium-rich fluid. 2. Isolated Malpighian tubules, unlike those of Rhodnius and Carausius secreted fluid containing elevated concentrations of magnesium. This transport displayed saturation kinetics, the half-maximal rate being at approximately 2·5 mM Mg. 3. Active transport of magnesium was demonstrated by the secretion of this cation against a tenfold concentration gradient and an electrical potential difference of 15 mV. 4. Magnesium ions are not required for fluid transport, which proceeds independently of magnesium transport. As a result fluid which is secreted slowly contains higher concentrations of magnesium than that which is secreted more rapidly. 5. Magnesium is transported by isolated Malpighian tubules fast enough to account for the observed excretion of magnesium in living mosquito larvae.

Active Transport of Sulphate Ions by the Malpighian Tubules of Larvae of the Mosquito Aedes Campestris

1975 ◽  
Vol 62 (2) ◽  
pp. 367-378
Author(s):  
S. H. P. MADDRELL ◽  
J. E. PHILLIPS
Keyword(s):  
Active Transport ◽  
Concentration Gradient ◽  
Electrical Potential ◽  
Malpighian Tubules ◽  
Potential Difference ◽  
Electrical Potential Difference ◽  
Sulphate Content ◽  
Anal Papillae ◽  
Tracer Experiments

1. Larvae of Aedes campestris ingest and absorb into their haemolymph large quantities of the sulphate-rich water in which they live, yet they are able to maintain the sulphate content of the haemolymph well below that of the environment. 2. Tracer experiments showed that sulphate regulation was not achieved by deposition of precipitates in the tissues. 3. In vitro preparations of Malpighian tubules secrete sulphate ions actively against both a three times concentration gradient and an electrical potential difference of 20 mV. This transport is half saturated at about 10 mM. 4. The rate of sulphate secretion by the Malpighian tubules is sufficient to remove all of the sulphate ingested by larvae living in waters which contain less than 100 mM of this anion. At higher concentrations, sulphate ions are probably also excreted elsewhere, perhaps by the rectum or anal papillae.

Sodium and Water Transport Across the Jejunum of Fasted Rats

1973 ◽  
Vol 51 (6) ◽  
pp. 405-409 ◽  
Author(s):  
Ivan T. Beck ◽  
P. K. Dinda
Keyword(s):  
Sodium Transport ◽  
Fluid Transport ◽  
Electrical Potential ◽  
Electrical Potential Difference ◽  
Serosal Side ◽  
Concomitant Increase ◽  
Net Flux ◽  
Unidirectional Fluxes ◽  
Mucosal Side ◽  
Fasted Rats

The effect of 72 h fasting on the transmural electrical potential difference (P.D.), the unidirectional fluxes, and the net flux of sodium and the net transport of fluid across the jejunum of rats was investigated. Everted jejunal segments were incubated in 12 ml of Krebs–Ringer bicarbonate solution containing 5.55 mM glucose on either side for 1 h at 37 °C. Seventy-two hours fasting caused a 63% increase in the transmural P.D., a 60% increase in the flux of Na from the mucosal to the serosal side, and a 48% increase in the flux of Na from the serosal to the mucosal side. The net mucosal to serosal Na flux increased by 97%. There was also a 41% increase in fluid transport across the intestine of fasted rats. The concomitant increase in sodium and fluid transport and in transmural P.D. is consistent with the current hypotheses of fluid and sodium transport.

An Investigation of the Role of Possible Neural Mechanisms in Cholera Toxin-Induced Secretion in Rabbit Ileal Mucosa in Vitro

1989 ◽  
Vol 77 (2) ◽  
pp. 161-166 ◽  
Author(s):  
K. J. Moriarty ◽  
N. B. Higgs ◽  
M. Woodford ◽  
L. A. Turnberg
Keyword(s):  
Cholera Toxin ◽  
Fluid Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Rabbit Ileum ◽  
Ileal Mucosa

1. Cholera toxin stimulates intestinal secretion in vitro by activation of mucosal adenylate cyclase. However, it has been proposed that cholera toxin promotes secretion in vivo mainly through an indirect mechanism involving enteric neural reflexes. 2. We examined this hypothesis further by studying the influence of neuronal blockade on cholera toxin-induced changes in fluid transport across rabbit ileum in vitro. Mucosa, stripped of muscle layers, was mounted in flux chambers and luminal application of crude cholera toxin (2 μg/ml) caused a delayed but sustained rise in the short-circuit current, electrical potential difference and Cl− secretion. Pretreatment with the nerve-blocking drug, tetrodotoxin (5 × 10−6 mol/l serosal side), failed to influence the secretory response to cholera toxin, and addition of tetrodotoxin at the peak response to cholera toxin also had no effect. 3. That tetrodotoxin could block neurally mediated secretagogues was confirmed by the demonstration that the electrical responses to neurotensin (10−7 mol/l and 10−8 mol/l) were blocked by tetrodotoxin (5 × 10−6 mol/l). Furthermore, the response to cholera toxin of segments of ileum, which included the myenteric, submucosal and mucosal nerve plexuses, was not inhibited by tetrodotoxin. 4. We conclude that cholera toxin-induced secretion in rabbit ileum in vitro is not mediated via a neurological mechanism.

Effect of furosemide on the electrical parameters of frog skin

1982 ◽  
Vol 243 (6) ◽  
pp. F581-F587 ◽  
Author(s):  
A. Corcia ◽  
S. R. Caplan
Keyword(s):  
Active Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Relative Increase ◽  
Electrical Potential Difference ◽  
Electrical Parameters ◽  
Active Conductance ◽  
Solution Bathing

When added to the mucosal solution bathing isolated frog skin at concentrations ranging from 5 X 10(-4) to 3 X 10(-3) M, the diuretic furosemide increased both the active transport of sodium and the electrical potential difference across the tissue in a dose-dependent way. The same effect was observed in chloride-free solutions. Mucosal furosemide also decreased the passive unidirectional fluxes of chloride. We believe that as far as electrical parameters are concerned mucosal furosemide has a double effect in frog skin: it increases the active conductance to sodium across the mucosal membrane, thus increasing active transport, and decreases the passive permeability to chloride, thus altering the passive conductance of the skin. The relative increase in short-circuit current was, however, invariably greater than the increase of the active conductance, suggesting the influence of yet a third effect. The effect of mucosal furosemide on active sodium transport was blocked by amiloride (5 X 1-(-5) M) and was independent of vasopressin. Qualitatively the effect was similar to the effect produced by triphenylmethylphosphonium ion.

scholarly journals Magnesium Regulation in Mosquito Larvae (Aedes Campestris) Living in Waters of High MgSO4 Content

1974 ◽  
Vol 61 (3) ◽  
pp. 749-760 ◽  
Author(s):  
J. KICENIUK ◽  
J. E. PHILLIPS
Keyword(s):  
Body Weight ◽  
Body Surface ◽  
Natural Waters ◽  
Magnesium Content ◽  
Malpighian Tubules ◽  
Urinary Concentration ◽  
Mosquito Larvae ◽  
Magnesium Ions ◽  
General Body ◽  
Magnesium Regulation

1. Although larvae of A. campestris can live in natural waters in which the magnesium content may vary seasonally from extremes of 1 to more than 100 mM, the haemolymph levels of magnesium vary only from 1·5 to 4 mM. 2. Larvae survive in water containing 90 mM-Mg and drink their own body weight every few hours, the ingested fluid and the magnesium ions being largely absorbed into the haemolymph via the midgut. 3. The urinary concentration of Mg2+ ions was always substantially higher than that of the external media and up to 23 times that of the haemolymph. 4. It is suggested that magnesium is not excreted across the general body surface, the Malpighian tubules and hindgut being largely responsible for removing magnesium from the haemolymph. 5. These physiological observations are discussed in relation to the environmental conditions under which larvae are naturally found.

scholarly journals Active Transport of Potassium by the Malpighian Tubules of Insects

1953 ◽  
Vol 30 (3) ◽  
pp. 358-369 ◽  
Author(s):  
J. A. RAMSAY
Keyword(s):  
Active Transport ◽  
Electrical Potential ◽  
Passive Diffusion ◽  
Malpighian Tubules ◽  
The Difference ◽  
Sodium And Potassium

1. The concentrations of sodium and potassium in the haemolymph and in the urine have been measured in eight species of insect. 2. The concentration of potassium in the urine is always greater than in the haemolymph. The concentration of sodium in the urine is generally less than in the haemolymph. 3. In seven of the species the difference of electrical potential across the wall of the tubule has also been measured. 4. In these seven species the results lead to the conclusion that potassium is actively secreted into the tubule. It is very probable that the same is true in the eighth case. 5. It seems likely that the excretion of sodium can be brought about by passive diffusion into the tubule.

Transport of electrolytes and water across wall of rabbit gall bladder

1963 ◽  
Vol 205 (3) ◽  
pp. 427-438 ◽  
Author(s):  
Henry O. Wheeler
Keyword(s):  
Solute Transport ◽  
Active Transport ◽  
Water Movement ◽  
Water Flux ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Coupling Mechanism ◽  
Electrical Potential Difference ◽  
Net Flux

Gall bladders of rabbits were studied in vitro in an apparatus which permitted measurement of electrical potential difference, net flux of water, and changes in electrolyte concentrations in mucosal and serosal fluid. Net water flux (mucosa to serosa) was directly proportional to net solute transport (measured as sodium flux) and the transported solution was slightly hypertonic. When mannitol was added to the mucosal fluid, water movement occurred against osmotic gradients often exceeding 80 mosmol/kg. Electrical potential differences were small, but the lumen was invariably positive. Flux ratio determinations indicated active transport of both chloride and sodium but not potassium. When isethionate was substituted for chloride, active bicarbonate absorption was also evident. Anion and cation transport were not independent and no transport occurred when choline was substituted for sodium. The evidence suggests coupled active transport of sodium and the major anions. Water movement is dependent upon active solute transport by means of an undetermined coupling mechanism.

Hepatic uptake of 3,5,3'-triiodothyronine: electrochemical driving forces

1992 ◽  
Vol 262 (6) ◽  
pp. G1104-G1112
Author(s):  
R. A. Weisiger ◽  
B. A. Luxon ◽  
R. R. Cavalieri
Keyword(s):  
Plasma Membrane ◽  
Active Transport ◽  
Driving Forces ◽  
Electrical Potential ◽  
Hepatic Uptake ◽  
Electrical Potential Difference ◽  
Multiple Indicator Dilution ◽  
Multiple Indicator ◽  
Basolateral Plasma Membrane ◽  
Uptake Process

We used the multiple indicator dilution technique to assess the electrochemical forces driving uptake of 3,5,3'-triiodo-L-thyronine (T3) across the basolateral plasma membrane in the single-pass perfused rat liver. With the use of 4 g/dl albumin solutions, the influx and efflux clearances were 0.020 +/- 0.005 and 0.0049 +/- 0.0017 (SE) ml.s-1.g liver-1, respectively, indicating that the total T3 concentration at equilibrium should be about four times greater in cytoplasm than in plasma. However, when the influx and efflux clearances were divided by the unbound (free) T3 concentration in the perfusate and cytosol, they were not different (3.76 +/- 0.26 vs. 4.30 +/- 0.38 ml.s-1.g liver-1), indicating that the uptake process does not generate a gradient of unbound T3 across the plasma membrane. To further test whether T3 uptake is driven by the electrical potential difference across the plasma membrane, liver cells were depolarized by isosmotic replacement of perfusate chloride with gluconate. There was no effect on uptake or efflux. To test whether uptake is coupled to influx of sodium, perfusate sodium was replaced with choline. Although there was a modest decline in both the influx and efflux clearances, there was no change in their ratio, as would be expected for sodium-coupled active transport. These results indicate that uptake of T3 across the basolateral hepatocyte membrane occurs by passive diffusion. We found no evidence to support concentrative, active transport by either electrogenic or sodium-coupled mechanisms.

Electrolyte composition of pulmonary alveolar subphase in anesthetized rabbits

1986 ◽  
Vol 60 (3) ◽  
pp. 972-979 ◽  
Author(s):  
D. W. Nielson
Keyword(s):  
Active Transport ◽  
Electrolyte Solution ◽  
Electrical Potential ◽  
Ionic Concentration ◽  
Electrolyte Composition ◽  
Potential Difference ◽  
Ion Fluxes ◽  
Electrical Potential Difference ◽  
Aqueous Subphase ◽  
Pleural Surface

We measured the concentration of Na+, K+, Ca2+, and Cl- in the aqueous subphase of the alveolar lining by puncturing the most superficial alveoli of the exposed lungs of anesthetized rabbits with ion-selective microelectrodes and a nonselective KCl microelectrode. A buffered electrolyte solution bathed the lung surface to keep it moist and warm (38 +/- 1 degrees C) and to serve as a reference for each measurement of ionic concentration. The serum and alveolar concentrations (meq/l) were Na+ 134 +/- 6 and 135 +/- 5, K+ 3.4 +/- 0.2 and 7.3 +/- 0.7, Ca2+ 3.1 +/- 0.2 and 3.2 +/- 0.4, and Cl- 106 +/- 7 and 103 +/- 5 (mean +/- SD). Only K+ was significantly different (P less than 0.001). There was a small electrical potential difference between the alveolar lumen and the pleural surface (-3.5 +/- 0.8 mV, lumen negative) that was significantly different from zero (P less than 0.001). Although it is not possible to measure ion fluxes with these techniques, the results are consistent with active transport of one or more of the ions studied.

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.

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