Active Transport by the Cecropia Midgut

1968 ◽  
Vol 48 (1) ◽  
pp. 1-12
Author(s):  
W. R. HARVEY ◽  
J. A. HASKELL ◽  
S. NEDERGAARD
Keyword(s):  
Transport Mechanism ◽  
Potassium Concentration ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Nernst Equation ◽  
Tissue Concentrations ◽  
Sodium Magnesium ◽  
Lines Of Evidence ◽  
Stimulation Of

1. From two lines of evidence, we conclude that the potassium transport gives rise directly to the midgut potential, i.e. that the active potassium transport mechanism is electrogenic. 2. First, diffusion potentials of neither potassium, sodium, magnesium, calcium, nor chloride could give rise to the large midgut potential if values for tissue concentrations are accepted for their respective activities in the epithelium. 3. Secondly, no externally added cation other than potassium is required to sustain either the potential or short circuit current, no specific anion is required, and no metabolic ion is known to be produced in sufficient amount to act as a counter ion for potassium in a non-electrogenic process. 4. Changes in the concentration of potassium on the blood-side of the midgut always lead to changes in potential in the direction predicted by the Nernst equation. Moreover, a tenfold change in potassium concentration leads to the expected 59 mV. potential change provided that the prior midgut potential is at least 130 mV. This effect could be attributed either to the stimulation of an electrogenic potassium pump or to a potassium diffusion potential across the blood-side barrier.

Comparison of Potassium Transport in Three Structurally Distinct Regions of The Insect Midgut

1981 ◽  
Vol 91 (1) ◽  
pp. 103-116
Author(s):  
MOIRA CIOFFI ◽  
WILLIAM R. HARVEY
Keyword(s):  
Goblet Cell ◽  
Apical Membrane ◽  
Close Association ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Structural Requirement ◽  
Posterior Midgut ◽  
New Information ◽  
Structural And Functional Properties

1. Active potassium transport across the isolated midgut of the Tobacco Hornworm larva, Manduca sexta, was studied by measuring the short circuit current (ISC) and unidirectional 42-potassium fluxes. 2. The midgut is composed of structurally distinct anterior, middle and posterior regions, all of which are shown to transport potassium, so that by comparing and contrasting their structural and functional properties new information on the mechanism of midgut potassium transport was obtained. 3. It has previously been shown that the potassium pump is located on the apical membrane of the goblet cell. In the anterior and middle regions of the midgut the goblet cell has a large cavity and mitochondria are closely associated with the apical membrane while in the posterior midgut the goblet cavity is much smaller, and mitochondria are not associated with the apical membrane. However, the apical membrane particles which have been implicated in active potassium transport in a number of other insect epithelia are present in all three regions. This observation suggests that the particles are a structural requirement for active transport, and that close association between mitochondria and the transporting membrane is not essential. 4. Comparison of the kinetic influx pool size and the differences in the ISC decay profiles between the three midgut regions suggest that part of the influx pool is a transported pool located in the goblet cavity. 5. A new model to explain the driving force for potassium transport in the midgut is proposed, in which the rate of potassium transport controls the entrance of potassium into the cell, rather than the opposite, currently accepted view.

Metabolic Support of Chloride-dependent Short-circuit Current Across Locust Rectum

1982 ◽  
Vol 99 (1) ◽  
pp. 349-362
Author(s):  
M. CHAMBERLIN ◽  
J. E. PHILLIPS
Keyword(s):  
Cyclic Amp ◽  
Short Circuit ◽  
Malpighian Tubule ◽  
Short Circuit Current ◽  
Metabolic Substrates ◽  
Endogenous Substrates ◽  
Tubule Fluid ◽  
Substrate Source ◽  
Stimulation Of

1. Recta of desert locusts were short-circuited and depleted of endogenous substrates by exposing them to saline containing cyclic AMP but no metabolites. Individual substrates were then added to substrate-depleted recta and the change in short-circuit current (Isc) monitored. 2. Proline or glucose (50 mM) caused by far the largest increase in Isc of all substrates tested. Stimulation of the Isc by proline was not dependent upon external sodium, but did require external chloride. 3. Physiological levels of proline also caused a large increase in Isc, while physiological levels of glucose produced a much smaller stimulation. Over 90% of the proline-dependent Isc stimulation can be produced by adding 15 mM proline solely to the lumen side of the tissue. 4. These results are discussed with regard to rectal oxidative metabolism and availability of metabolic substrates in vivo. High levels of proline in Malpighian tubule fluid are probably the major substrate source for rectal Cl−transport. Note:

Active transport of magnesium across the isolated midgut of Hyalophora cecropia

1975 ◽  
Vol 63 (2) ◽  
pp. 313-320
Author(s):  
J. L. Wood ◽  
A. M. Jungreis ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Magnesium Concentration ◽  
Magnesium Transport ◽  
Wet Weight ◽  
Net Flux ◽  
Burk Plot

1. The 28Mg-measured net flux of magnesium from lumen-side to haemolymph-side of the isolated and short-circuited midgut was 1.97 +/− 0.28 mu-equiv cm(−2) /(−1) in 8 mM-Mg2+. 2. The magnesium-influx shows a delay before the tracer steady-state is attained, indicating the existence of a magnesium-transport pool equivalent to 6.7 mu-equiv/g wet weight of midgut tissue. 3. Magnesium depresses the short-circuit current produced the midgut but not the potassium transport, the depression being equal to the rate of magnesium transport. 4. Magnesium transport yields a linear Lineweaver-Burk plot with an apparent Km of 34 mM-Mg2+ and an apparent Vmax of 14.9 mu-equiv cm(−1) /(−1). 5. Magnesium is actively transported across the midgut and contributes to the regulation of the haemolymph magnesium concentration in vivo.

Bathing Solution Tonicity and Potassium Transport by the Midgut of the Tobacco Hornworm Manduca Sexta

1979 ◽  
Vol 78 (1) ◽  
pp. 213-223
Author(s):  
DAVID F. MOFFETT
Keyword(s):  
Manduca Sexta ◽  
Short Circuit ◽  
Weight Ratio ◽  
Short Circuit Current ◽  
Dry Weight ◽  
Potassium Transport ◽  
Bathing Solution ◽  
Histological Studies ◽  
Wet Weight ◽  
Small Solute

Potassium transport by the isolated midgut of Manduca larvae, as measured by the short circuit current, is inhibited by substitution of small organic solutes (M.W. < 340) for the sucrose normally included in bathing solution formulated for this tissue. Other solutes of molecular weight equal to or greater than sucrose are essentially as effective as sucrose in promoting the short circuit current. Equilibration of midgut in solutions containing the small solute mannitol results in a decrease in the dry weight/wet weight ratio of the tissue, suggesting that the small solutes can penetrate into areas of the tissue which are not accessible to sucrose. Histological studies suggest that sites of swelling in the presence of mannitol include both cytoplasm and goblet cell lumen. The inhibition of the short circuit current is rapidly reversible on return to bathing solution containing sucrose or another large solute. The effect of small solutes probably does not involve compromise of the energy source for potassium transport since oxygen uptake is unchanged in the presence of a small solute.

scholarly journals Acid-Base Transport and Control in Locust Hindgut: Artefacts Caused by Short-Circuit Current

1991 ◽  
Vol 155 (1) ◽  
pp. 455-467
Author(s):  
R. BRENT THOMSON ◽  
N. AUDSLEY ◽  
JOHN E. PHILLIPS
Keyword(s):  
Cyclic Amp ◽  
Acid Secretion ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Salt Bridges ◽  
Electrical Parameters ◽  
Acid Base ◽  
Before And After ◽  
And Control ◽  
Stimulation Of

The commonly used method of passing short-circuit current (Isc) across insect epithelia through Ag-AgCl electrodes, without the use of salt bridges, leads to significant OH− production at the cathode (lumen side) when high currents are applied. The alkalization of the lumen previously reported when cyclic AMP was added to short-circuited locust hindgut is a result of this phenomenon rather than cyclic-AMP-mediated stimulation of acid-base transport in the hindgut. When salt bridges are used to pass short-circuit current across locust hindgut, acid secretion (JH) into the lumen equals alkaline movement (JOH) to the haemocoel side, and JH is similar under both open- and short-circuit conditions. JH is similar (1.5 μequiv cm−2 h−1) in recta and ilea. Addition of cyclic AMP inhibits JH across the rectum by 42–66%, but has no effect on the ileum when salt bridges are used. Electrical parameters (Isc, Vt, Rt) reflecting hindgut Cl− transport (JCL) before and after stimulation with cyclic AMP are the same whether or not salt bridges are used. We found no evidence of any coupling between JCl and JH/JOH.

Forskolin-induced HCO3- current across apical membrane of the frog corneal epithelium

1990 ◽  
Vol 259 (2) ◽  
pp. C215-C223 ◽  
Author(s):  
O. A. Candia
Keyword(s):  
Corneal Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Pump Current ◽  
Gas Composition ◽  
Apical Side ◽  
Disulfonic Stilbene ◽  
Stimulation Of

Forskolin (and other Cl- secretagogues) does not affect the very small Na(+)-originated short-circuit current (Isc) across frog corneal epithelium bathed in Cl- free solutions. However, forskolin in combination with increased PCO2 bubbling of the solutions (5-20% CO2) stimulated Isc proportionally to PCO2 to a maximum of approximately 8 microA/cm2. This current could be eliminated and reinstated by sequentially changing the gas composition of the bubbling to 100% air and 20% CO2-80% air. The same effects were observed when PCO2 changes were limited to the apical-side solution. Stroma-to-tear HCO3- movement was deemed unlikely, since the increase in Isc was observed with a HCO3(-)-free solution on the stromal side and CO2 gassing limited to the tear side. From the effects of ouabain and tryptamine, at least 80% of the Isc across the basolateral membrane can be accounted for by the Na+ pump current plus K+ movement from cell to bath. Methazolamide also inhibited Isc. Current across the apical membrane cannot be attributed to an electronegative Na(+)-HCO3- symport given the insensitivity of Isc to a disulfonic stilbene and the fact that stroma-to-tear Na+ fluxes did not increase on stimulation of Isc. The tear-to-stroma Na+ flux also remained unaltered, negating an increased apical bath-to-cell Na+ flow. The forskolin-20% CO2 manipulation produced a depolarization of the intracellular potential, a reduction in the apical-to-basolateral resistance ratio, and a decrease in transepithelial resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological regulation of colonic ion transport

1989 ◽  
Vol 256 (2) ◽  
pp. G396-G403 ◽  
Author(s):  
D. A. Russell ◽  
G. A. Castro
Keyword(s):  
Guinea Pigs ◽  
Trichinella Spiralis ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Antigenic Stimulation ◽  
Synthesis Inhibitor ◽  
Combined Use ◽  
Maximum Elevation ◽  
Prostaglandin Synthesis Inhibitor ◽  
Stimulation Of

Challenge of distal colonic epithelium from Trichinella spiralis-infected guinea pigs with parasite-derived antigen elevated short-circuit current (Isc) for approximately 60 min. The maximum elevation (delta Isc) was approximately 250 microA/cm2 at 5 min after the addition of trichinella antigen. The antigen-induced alterations in Isc were of greater magnitude and duration than those evoked in jejunum. Colonic electrical resistance was transiently reduced after exposure to antigen. There was no significant effect of antigen on electrical parameters of colon from nonimmunized (uninfected) guinea pigs. The antihistamine pyrilamine (10(-5) M) and the prostaglandin synthesis inhibitor indomethacin (10(-6) M) reduced the colonic Isc response to antigen by 40% when used in combination but had insignificant effects when used singly. In contrast, the jejunal Isc response to antigen was totally eliminated by the combined use of those inhibitors. Antigenic stimulation of sensitized colon released histamine and prostaglandin E2 (PGE2). However, the histamine released was only about one-tenth that stimulated by antigen in the jejunum, and PGE2 released was only one-tenth of that stimulated by bradykinin in the colon. PGE2 was not released after antigenic stimulation of jejunum. The antigen-induced colonic delta Isc was reduced approximately 50% by either furosemide or tetrodotoxin. Although histamine- and indomethacin-sensitive factors contribute greatly to the mediation of the antigen-induced delta Isc in jejunum, these autacoids contribute to a lesser extent to the antigen-induced delta Isc in guinea pig colon.

Modulation of aldosterone-induced stimulation of ENaC synthesis by changing the rate of apical Na+ entry

2001 ◽  
Vol 281 (4) ◽  
pp. F687-F692 ◽  
Author(s):  
Lisette Dijkink ◽  
Anita Hartog ◽  
Carel H. Van Os ◽  
René J. M. Bindels
Keyword(s):  
Feedback Inhibition ◽  
Collecting Duct ◽  
Short Circuit ◽  
Primary Cultures ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Cortical Collecting Duct ◽  
Entry Rate ◽  
Protein Levels ◽  
Stimulation Of

Primary cultures of immunodissected rabbit connecting tubule and cortical collecting duct cells were used to investigate the effect of apical Na+ entry rate on aldosterone-induced transepithelial Na+ transport, which was measured as benzamil-sensitive short-circuit current ( I sc). Stimulation of the apical Na+ entry, by long-term short-circuiting of the monolayers, suppressed the aldosterone-stimulated benzamil-sensitive I sc from 320 ± 49 to 117 ± 14%, whereas in the presence of benzamil this inhibitory effect was not observed (335 ± 74%). Immunoprecipitation of [35S]methionine-labeled β-rabbit epithelial Na+ channel (rbENaC) revealed that the effects of modulation of apical Na+ entry on transepithelial Na+ transport are exactly mirrored by β-rbENaC protein levels, because short-circuiting the monolayers decreased aldosterone-induced β-rbENaC protein synthesis from 310 ± 51 to 56 ± 17%. Exposure to benzamil doubled the β-rbENaC protein level to 281 ± 68% in control cells but had no significant effect on aldosterone-stimulated β-rbENaC levels (282 ± 68%). In conclusion, stimulation of apical Na+ entry suppresses the aldosterone-induced increase in transepithelial Na+transport. This negative-feedback inhibition is reflected in a decrease in β-rbENaC synthesis or in an increase in β-rbENaC degradation.

Hormonal regulation of Na+-K+-ATPase in cultured epithelial cells

1986 ◽  
Vol 251 (2) ◽  
pp. C186-C190 ◽  
Author(s):  
J. P. Johnson ◽  
D. Jones ◽  
W. P. Wiesmann
Keyword(s):  
Enzyme Activity ◽  
Epithelial Cells ◽  
Atpase Activity ◽  
Hormonal Regulation ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Toad Urinary Bladder ◽  
A6 Cells ◽  
Cultured Epithelial Cells ◽  
Stimulation Of

Aldosterone and insulin stimulate Na+ transport through mechanisms involving protein synthesis. Na+-K+-ATPase has been implicated in the action of both hormones. We examined the effect of aldosterone and insulin on Na+-K+-ATPase in epithelial cells in culture derived from toad urinary bladder (TB6C) and toad kidney (A6). Aldosterone, but not insulin, increases short-circuit current (ISC) in TB6C cells. Aldosterone increases Na+-K+-ATPase activity after 18 h of incubation, but no effect can be seen at 3 and 6 h. Amiloride, which inhibits aldosterone-induced increases in ISC, has no effect on either basal or aldosterone stimulated enzyme activity. Both aldosterone and insulin increase ISC in A6 cells and when added together are synergistic. Aldosterone stimulates enzyme activity in A6 cells, but insulin alone has no effect. However, aldosterone and insulin together stimulate enzyme activity more than aldosterone alone. It appears that stimulation of Na+-K+-ATPase activity is involved in aldosterone action in both cell lines but does not appear to be due to increased Na+ entry, since enhanced enzyme activity is not inhibited by amiloride. In contrast, insulin alone has no direct effect on Na+-K+-ATPase, although the increased enzyme activity following both agents in combination may explain their synergism on ISC.

Changes in intracellular sodium with chloride secretion in dog tracheal epithelium

1986 ◽  
Vol 250 (4) ◽  
pp. C646-C650 ◽  
Author(s):  
S. R. Shorofsky ◽  
M. Field ◽  
H. A. Fozzard
Keyword(s):  
Steady State ◽  
Kinetic Models ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Chloride Secretion ◽  
Tracheal Epithelium ◽  
Cl Secretion ◽  
Intracellular Na Activity ◽  
Sufficient Energy ◽  
Stimulation Of

Na-selective microelectrodes were employed to investigate the mechanism of Cl secretion by canine tracheal epithelium. In control tissues with a mean short-circuit current (Isc) of 30.1 microA/cm2, the intracellular Na activity (aiNa) was 10.7 mM. Following steady-state stimulation of Cl secretion with epinephrine (Isc = 126.4 microA/cm2), aiNa was 21.3 mM. These data indicate that there is sufficient energy in the Na gradient to drive Cl secretion by this tissue. When analyzed with simple kinetic models for the Na-K pump, they also suggest that the basolateral entry step involves the Na-K-2Cl cotransporter.

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