Electrophysiology of K+ Transport by Midgut Epithelium of Lepidopteran Insect Larvae: II. The Transapical Electrochemical Gradients

1988 ◽  
Vol 135 (1) ◽  
pp. 39-49
Author(s):  
DAVID F. MOFFETT ◽  
ALAN R. KOCH
Keyword(s):  
Electrical Potential ◽  
Potential Gradient ◽  
Goblet Cells ◽  
Mean Value ◽  
Bathing Solution ◽  
Voltage Sensitivity ◽  
Apical Surface ◽  
Insect Larvae ◽  
Lepidopteran Insect ◽  
K Transport

The apical surface of the midgut of Manduca sexta larvae is composed of the apical membranes of columnar cells, in the form of microvilli, and the apical goblet of goblet cells. Considerable evidence has suggested that the apical electrogenic pump that is responsible for transepithelial K+ transport is located on the apical membrane of goblet cells. In the present study the transapical potentials and K+ chemical activity [(K+)] gradients of columnar and goblet cells of posterior midgut were examined in the short-circuited gut. In some experiments the recording site was localized by ionophoresis of NiCl2 followed immediately by fixation in rubeanic acid. The (K+) of goblet cavities was substantially higher than that of the free solution on the gut luminal side (mean value of 94mmoll−1 in standard bathing solution). The goblet cavity was electrically positive to the gut lumen (mean value of 40 mV in standard bathing solution). When the rate of pumping of K+ into the goblet cavity was decreased by hypoxia or decreased bathing solution [K+], the electrical potential gradient between cytoplasm and goblet cavity decreased while intracellular (K+) and goblet cavity (K+) were relatively stable. These studies provide evidence that a negatively charged goblet matrix is present in goblet cavities. Furthermore, they suggest that it is the voltage-sensitivity of the apical pump to the electrical component of the transapical electrochemical gradient, and not a concentrationdependence of the pump, that exercises the major role in determining the relationship between extracellular (K+) and net K+ transport by the isolated gut.

scholarly journals Electrophysiology of K+ Transport by Midgut Epithelium of Lepidopteran Insect Larvae: The Transbasal Electrochemical Gradient

1988 ◽  
Vol 135 (1) ◽  
pp. 25-38 ◽  
Author(s):  
DAVID F. MOFFETT ◽  
ALAN R. KOCH
Keyword(s):  
Lucifer Yellow ◽  
Electrical Coupling ◽  
Basal Membrane ◽  
Cell Types ◽  
Transepithelial Transport ◽  
Electrochemical Gradient ◽  
Insect Larvae ◽  
Lepidopteran Insect ◽  
Columnar Cells ◽  
K Transport

Basal membrane potential (Vb) and intracellular K+ activity [(K+)i] were recorded, using microelectrodes, in isolated, superfused, short-circuited midgut of fifth instar larvae of Manduca sexta. The electrochemical gradient across the basal membrane was favourable for K+ entry as long as [K+]b was 32mequivl−1 or greater. In 20 mequiv 1−1 K+ Vb rose so that in some cells the basal electrochemical gradient was unfavourable for K+ entry. In 10 mequivl−1 K+, the basal electrochemical gradient of all cells was unfavourable for K+ entry. This result suggests that an active K+ pump may augment passive basal K+ entry. Addition of 2mmoll−1 Ba2+ to midgut resulted in substantial hyperpolarization of Vb accompanied by relatively small changes in (K+)i; the net effect was to move (K+); farther away from electrochemical equilibrium with external K+. Identification of recorded cells by ionophoretic injection of Lucifer Yellow showed that both major cell types of the epithelium (goblet and columnar cells) had similar control values of Vb and (K+)i; and responded similarly to Ba2+, suggesting the presence of effective chemical or electrical coupling between the transporting goblet cells and the non-transporting columnar cells. Hypoxia reduced transepithelial K+ transport, both in the absence and in the presence of Ba2+. In the absence of Ba2+, (K+)i; was within a few millivolts of equilibrium and the effect of hypoxia was small. In the presence of Ba2+, when (K+)i; was far from equilibrium with extracellular K+, hypoxia markedly depolarized the basal membrane. The results are compatible with the suggestion that Ba2+ partially blocks basal K+ entry, but does not directly affect the apical pump. Hypoxia inhibits the apical pump. Since the active transepithelial transport of K+ was reduced after Ba2+ treatment even though (K+)i; was unchanged, it appears that the activity of the apical pump is primarily controlled by the voltage step across the apical membrane.

Intracellular ion activities and Cl-transport mechanisms in bullfrog corneal epithelium

1983 ◽  
Vol 244 (5) ◽  
pp. C336-C347 ◽  
Author(s):  
L. Reuss ◽  
P. Reinach ◽  
S. A. Weinman ◽  
T. P. Grady
Keyword(s):  
Cell Membrane ◽  
Corneal Epithelium ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Bathing Solution ◽  
Apical Surface ◽  
Equivalent Circuit Analysis ◽  
Cl Transport ◽  
Cl Permeability

Cell membrane potentials, cell membrane resistances, and intracellular ionic activities were measured in bullfrog corneal epithelium. Equivalent circuit analysis was performed by adding adenosine to the apical surface and assuming that only the apical membrane is initially affected. From single-ion substitutions in the apical bathing solution, the apical membrane was found to have a high Cl- permeability, a low K+ permeability, and an unmeasurably small Na+ permeability. Under control conditions intracellular Cl- activity (aCli) was 22 +/- 2 (SE) mM, intracellular Na+ activity (aNai) was 14 +/- 3 mM, and intracellular K+ activity (aKi) was 106 +/- 5 mM. The electrical potential differences across apical and basolateral membranes were about 50 and 67 mV, respectively, both cell negative. aCli and aKi are higher, whereas aNai is much lower than predicted for equilibrium distribution. Inasmuch as Cl- is transported from the basolateral (stromal) to the apical (tear) side, basolateral entry of this anion is uphill and apical exit is downhill. Basolateral entry is Na+ dependent, as evidenced by a fall of aCli to near-equilibrium values after basolateral Na+ removal. The electrochemical gradient for Cl- efflux across the apical membrane is large enough to account for Cl- transport by electrodiffusion only. Na+ removal from the basolateral solution causes a reversible decrease of apical membrane Cl- permeability. The results support the hypothesis that net transepithelial Cl- transport results from coupled NaCl entry (or an equivalent process) at the basolateral membrane and electrodiffusional Cl- exit at the apical membrane.

scholarly journals Driving forces and pathways for H+ and K+ transport in insect midgut goblet cells.

1992 ◽  
Vol 172 (1) ◽  
pp. 403-415 ◽  
Author(s):  
D F Moffett ◽  
A Koch
Keyword(s):  
Driving Forces ◽  
Goblet Cells ◽  
Bathing Solution ◽  
Entry And Exit ◽  
Insect Midgut ◽  
Lepidopteran Insects ◽  
Lateral Intercellular Spaces ◽  
K Secretion ◽  
K Transport ◽  
Primary Active Transport

In the midgut of larval lepidopteran insects, goblet cells are believed to secrete K+; the proposed mechanism involves an electrogenic K+/nH+ (n > 1) antiporter coupled to primary active transport of H+ by a vacuolar-type ATPase. Goblet cells have a prominent apical cavity isolated from the gut lumen by a valve-like structure. Using H(+)- and K(+)-selective microelectrodes, we showed that electrochemical gradients of H+ and K+ across the apical membrane and valve are consistent with active secretion of both ions into the cavity and that the transapical H+ electrochemical gradient, but not the transapical pH gradient, is competent to drive K+ secretion by a K+/nH+ antiporter. We used 10 mmol l-1 tetramethylammonium ion (TMA+) as a marker for the ability of small cations to pass from the gut lumen through the valve to the goblet cavity, exploiting the high TMA+ sensitivity of 'K(+)-sensitive' microelectrodes. These studies showed that more than half of the cavities were inaccessible to TMA+. For those cavities that were accessible to TMA+, both entry and exit rates were too slow to be consistent with direct entry through the valves. One or more mixing compartments appear to lie between the lumen bathing solution and the goblet cavity. The lateral intercellular spaces and goblet cell cytoplasm are the most likely compartments. The results are not consistent with free diffusion of ions in a macroscopic valve passage; mechanisms that would allow K+ secreted into the goblet cavity to exit to the gut lumen, while preventing H+ from exiting, remain unclear.

A method of determining electrical potential gradient across mitochondrial membrane in perfused rat hearts

1993 ◽  
Vol 265 (2) ◽  
pp. H445-H452 ◽  
Author(s):  
B. Wan ◽  
C. Doumen ◽  
J. Duszynski ◽  
G. Salama ◽  
K. F. LaNoue
Keyword(s):  
Mitochondrial Membrane ◽  
Electrical Potential ◽  
Potential Gradient ◽  
Order Rate Constant ◽  
Isolated Rat Heart ◽  
First Order ◽  
Order Rate ◽  
Rat Hearts ◽  
Perfused Rat Hearts ◽  
Electrical Potential Gradient

The electrical potential gradient across the mitochondrial membrane (delta psi m) in perfused rat hearts was estimated by calculating the equilibrium distribution of the lipophilic cation tetraphenylphosphonium (TPP+), using measured kinetic constants of uptake and release of TPP+. First-order rate constants of TPP+ uptake were measured during 30-min perfusions of intact rat hearts with tracer amounts (5.0 nM) of tritium-labeled TPP+ ([3H]TPP+) in the perfusate. This was followed by a 30-min washout, during which the first-order rate constant of efflux was estimated. Values of [3H]TPP+ outside the heart and total [3H]TPP+ inside the heart at equilibrium were calculated. From this information and separately estimated time-averaged plasma membrane potentials (delta psi c) it was possible to calculate free cytosolic [3H]TPP+ at equilibrium. It was also possible to calculate free intramitochondrial [3H]TPP+ at equilibrium as the difference between total tissue [3H]TPP+ minus free cytosolic TPP+ and the sum of all the bound [3H]TPP+. Bound [3H]TPP+ was determined from [3H]TPP+ binding constants measured in separate experiments, using both isolated mitochondria and isolated cardiac myocytes under conditions where both delta psi m and delta psi c were zero. Delta psi m was calculated from the intramitochondrial and cytosolic free TPP+ concentrations using the Nernst equation. Values of delta psi m were 144.9 +/- 2.0 mV in hearts perfused with 5 mM pyruvate and 118.2 +/- 1.4 mV in hearts perfused with 11 mM glucose, in good agreement with delta psi m obtained from isolated rat heart mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)

Barium inhibition of basolateral membrane potassium conductance in tracheal epithelium

1983 ◽  
Vol 244 (6) ◽  
pp. F639-F645 ◽  
Author(s):  
M. J. Welsh
Keyword(s):  
Driving Force ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Potassium Conductance ◽  
Short Circuit Current ◽  
Electrical Circuit ◽  
Tracheal Epithelium ◽  
Bathing Solution ◽  
K Permeability

Addition of barium ion, Ba2+, to the submucosal bathing solution of canine tracheal epithelium reversibly decreased the short-circuit current and increased transepithelial resistance. The decrease in short-circuit current represented a decrease in the net rate of Cl secretion with no change in the rate of Na absorption. Intracellular microelectrode techniques and an equivalent electrical circuit analysis were used to localize the effect of Ba2+ to an inhibition of the permeability of the basolateral membrane to K. Ba2+ (2 mM) doubled basolateral membrane resistance, decreased the equivalent electromotive force at the basolateral membrane, and decreased the magnitude of the depolarization of basolateral membrane voltage produced by increasing the submucosal K concentration. The inhibition of the basolateral K permeability depolarized the negative intracellular voltage, resulting in both a decrease in the driving force for Cl exit and an estimated increase in intracellular Cl concentration. These studies indicate that there is a Ba2+-inhibitable K conductance at the basolateral membrane of tracheal epithelial cells and that the K permeability plays an important role in the generation of the negative intracellular electrical potential that provides the driving force for Cl exit from the cell.

Electrophysiology of renal capillary membranes: gel concept applied and Starling model challenged

1988 ◽  
Vol 254 (3) ◽  
pp. F364-F373 ◽  
Author(s):  
M. Wolgast ◽  
G. Ojteg
Keyword(s):  
Charge Density ◽  
Electrical Potential ◽  
Potential Gradient ◽  
Swelling Pressure ◽  
Porous Membrane ◽  
Fixed Charge ◽  
Fixed Charge Density ◽  
Capillary Membranes ◽  
External Forces ◽  
Gel Membranes

In the classical Starling model the hydrostatic pressure in the pores is generally lower than that in capillary plasma, a phenomenon that necessitates the assumption of a rigid porous membrane. In flexible gel membranes, the capillary pressure is suggested to be balanced by a gel swelling pressure generated by negative fixed charges. Regarding the fluid transfer, the transmembranous electrical potential gradient will generate a net driving electroosmotic force. This force will be numerically similar to the net driving Starling force in small pores, but distinctly different in large pores. From previous data on the hydrostatic and colloid osmotic forces, the fixed charge density at the two interfaces of 1) the glomerular and 2) the peritubular capillary membrane were calculated and used to predict the flux of a series of charged protein probes. The close fit to the experimental data in both the capillary beds is in line with the gel concept presented. The gel concept (but hardly a rigid membrane) explains the ability of capillary membranes to alter their permeability in response to external forces. Gel membranes can furthermore be predicted to have a self-rinsing ability, as entrapped proteins will increase the local fixed charge density, leading to fluid entry into the region between the particle and the pore rim, which by consequent widening of the channel will facilitate extrusion of trapped proteins.

Apical acidification by rabbit papillary surface epithelium

1990 ◽  
Vol 258 (4) ◽  
pp. F893-F899 ◽  
Author(s):  
P. S. Chandhoke ◽  
R. K. Packer ◽  
M. A. Knepper
Keyword(s):  
Surface Area ◽  
Collecting Duct ◽  
Ussing Chamber ◽  
Renal Stones ◽  
Surface Epithelium ◽  
Bathing Solution ◽  
Unit Surface Area ◽  
Apical Surface ◽  
Total Acid ◽  
Medullary Collecting Duct

The rabbit papillary surface epithelium (PSE) is a simple cuboidal epithelium that covers the outer surface of the renal papilla and has an apical surface that faces the urinary space. We studied acid-base transport in this epithelium by dissecting it from the papilla, mounting it in a modified Ussing chamber, and following pH changes in the apical bathing solution. The experiments demonstrated that the PSE is capable of acidifying the apical solution at a substantial rate. The acidification rate was similar with 100% nitrogen and 100% oxygen (with and without 10 microM antimycin A), ruling out a dependence on oxidative metabolism. Addition of 1 mM iodoacetate decreased apical acidification by 55%, suggesting a dependence on glycolysis. The net rate of lactate secretion was only 17% of the total acid secretion rate, indicating that apical acidification was not directly caused by secretion of lactic acid alone. Removal of sodium or potassium from the apical solutions or the addition of 1 mM N-ethylmaleimide failed to eliminate the apical acidification. Although the rate of PSE apical acidification is comparable to that of the rabbit outer medullary collecting duct (on a unit surface area basis), its contribution to urinary net acid excretion is likely to be small, owing to the small relative surface area of the PSE. However, by altering the pH of urine locally within the pelvic recesses, the PSE has the potential of modifying the formation of renal stones within the pelvic recesses.

The Epidermo-Peritoneal Potential in Patients Treated with Continuous Ambulatory Peritoneal Dialysis

1993 ◽  
Vol 16 (2) ◽  
pp. 71-74 ◽  
Author(s):  
A. Davenport ◽  
S.F. Dealler
Keyword(s):  
Electrical Potential ◽  
Potential Gradient ◽  
Subsequent Infection ◽  
Duration Of Treatment ◽  
Bacterial Peritonitis ◽  
Bacterial Migration ◽  
Skin Commensals ◽  
History Of ◽  
The Mean ◽  
End Stage

At physiologic pH, S. epidermidis moves along an electrical potential gradient. We measured the epidermo-peritoneal electrical potential (EPP) in 23 end-stage renal failure patients treated with CAPD. There was a negative correlation between the mean EPP and the patient's age (r=0.47, p=0.016), but no correlation between the mean EPP and the duration of treatment (r=0.003, p=0.5). The EPP was greater in those patients with a history of recurrent bacterial peritonitis due to S. epidermidis [median EPP 23 mv (95% confidence limits 16-51)] compared to those with only one or no episodes of bacterial peritonitis due to S. epidermidis infection [11 mv (9-17), p<0.05]. Thus electrical gradients caused by the presence of the CAPD catheter could contribute to colonisation and subsequent infection by skin commensals, by aiding bacterial migration.

scholarly journals Ion Transport in Hydrodictyon africanum

1967 ◽  
Vol 50 (6) ◽  
pp. 1607-1625 ◽  
Author(s):  
J. A. Raven
Keyword(s):  
Free Energy ◽  
Low Temperature ◽  
Electrical Potential ◽  
Bathing Solution ◽  
Electrical Potential Difference ◽  
Energy Gradient ◽  
Na Efflux ◽  
K Concentration ◽  
Net Fluxes ◽  
External K

The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.

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