Lidocaine and Barium Distinguish Separate Routes of Transbasal K+ Uptake in the Posterior Midgut of the Tobacco Hornworm (Manduca Sexta)

1991 ◽  
Vol 157 (1) ◽  
pp. 243-256 ◽  
Author(s):  
DAVID F. MOFFETT ◽  
ALAN KOCH
Keyword(s):  
Intracellular Transport ◽  
Channel Blocker ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Basal Membrane ◽  
Tobacco Hornworm ◽  
K Channel ◽  
K Uptake ◽  
Posterior Midgut ◽  
K Transport

The isolated posterior midgut of the tobacco hornworm maintains a vigorous transepithelial K+ transport from the hemolymphal side to the lumen side at a rate accurately measured by its short-circuit current. Previous studies using the K+ channel blocker Ba2+ suggested that partial inhibition of the short-circuit current by hemolymphal Ba2+ was due to blockage of one of at least two parallel transbasal entry routes for K+ into the intracellular transport pool. The present studies show that the local anesthetic lidocaine, at a concentration of 5 mmoll−1 on the hemolymphal side, partly inhibits net transepithelial K+ transport. The inhibition is accompanied by hyperpolarization of the basal membrane and an increase in transbasal resistance, suggestive of a block of transbasal K+ conductance. The effects of lidocaine and Ba2+ are additive, suggesting that the inhibitors distinguish separate, parallel K+ uptake processes.

Basal membrane uptake in potassium-secreting cells of midgut of tobacco hornworm (Manduca sexta)

1990 ◽  
Vol 258 (1) ◽  
pp. R112-R119
Author(s):  
A. C. Chao ◽  
A. R. Koch ◽  
D. F. Moffett
Keyword(s):  
Manduca Sexta ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Basal Membrane ◽  
Bathing Solution ◽  
K Uptake ◽  
Active Secretion ◽  
Uptake Process ◽  
Intracellular K Activity ◽  
K Activity

Basal membrane voltage (Vb), intracellular K+ activity [(K+)i], and short-circuit current (Isc) were measured in isolated posterior midguts of Manduca sexta wherein Isc is a measured of active secretion of K+ from blood into lumen. When bathed in 32 mM K+ and exposed to 100% O2, average values were Isc = 244 microAmp/cm2, Vb = -33.1 mV, and (K+)i = 88.6 mM. The electrochemical gradient across the basal membrane (d mu) averaged +5.8 mV (a gradient favorable for K+ entry). Exposure to 5% O2 led to a new steady state in which Isc = 71 microAmp/cm2, Vb = -18.7 mV, and (K+)i = 99.4 mM. During hypoxia, d mu averaged -9.9 mV (a gradient unfavorable for K+ entry). When the external bathing solution was 10 mM K+, comparable values were, for 100% O2, Isc = 139 microAmp/cm2, Vb = -56.1 mV, (K+)i = 72.2 mM, and d mu = +3.6 mV, and in 5% O2 the values were Isc = 28.3 microAmp/cm2, Vb = -43.7 mV, (K+)i = 76.1 mM, and d mu = -10.2 mV. The failure of cellular K+ to fall during prolonged hypoxia is evidence for a thermodynamically active basal K+ uptake process.

scholarly journals Na+ and K+ transport at basolateral membranes of epithelial cells. II. K+ efflux and stoichiometry of the Na,K-ATPase.

1986 ◽  
Vol 87 (3) ◽  
pp. 485-502 ◽  
Author(s):  
T C Cox ◽  
S I Helman
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Pump Current ◽  
Ringer Solution ◽  
K Channel ◽  
Na Transport ◽  
Transepithelial Na Transport ◽  
Dependent Component ◽  
Na Efflux ◽  
K Transport

Changes of 42K efflux (J23K) caused by ouabain and/or furosemide were measured in isolated epithelia of frog skin. From the kinetics of 42K influx (J32K) studied first over 8-9 h, K+ appeared to be distributed into readily and poorly exchangeable cellular pools of K+. The readily exchangeable pool of K+ was increased by amiloride and decreased by ouabain and/or K+-free extracellular Ringer solution. 42K efflux studies were carried out with tissues shortcircuited in chambers. Ouabain caused an immediate (less than 1 min) increase of the 42K efflux to approximately 174% of control in tissues incubated either in SO4-Ringer solution or in Cl-Ringer solution containing furosemide. Whereas furosemide had no effect on J23K in control tissues bathed in Cl-rich or Cl-free solutions, ouabain induced a furosemide-inhibitable and time-dependent increase of a neutral Cl-dependent component of the J23K. Electroconductive K+ transport occurred via a single-filing K+ channel with an n' of 2.9 K+ efflux before ouabain, normalized to post-ouabain (+/- furosemide) values of short-circuit current, averaged 8-10 microA/cm2. In agreement with the conclusions of the preceding article, the macroscopic stoichiometry of ouabain-inhibitable Na+/K+ exchange by the pump was variable, ranging between 1.7 and 7.2. With increasing rates of transepithelial Na+ transport, pump-mediated K+ influx saturated, whereas Na+ efflux continued to increase with increases of pump current. In the usual range of transepithelial Na+ transport, regulation of Na+ transport occurs via changes of pump-mediated Na+ efflux, with no obligatory coupling to pump-mediated K+ influx.

Changes in midgut active ion transport and metabolism during larval-larval molting in the tobacco hornworm (Manduca sexta)

1997 ◽  
Vol 200 (3) ◽  
pp. 643-648 ◽  
Author(s):  
M Chamberlin ◽  
C Gibellato ◽  
R Noecker ◽  
E Dankoski
Keyword(s):  
Ion Transport ◽  
Manduca Sexta ◽  
Aerobic Capacity ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Tobacco Hornworm ◽  
Maximal Aerobic Capacity ◽  
Posterior Midgut ◽  
Molting Process ◽  
Active Ion Transport

Ion transport and metabolism in the posterior midgut before, during and after the molt to the fifth instar of the tobacco hornworm Manduca sexta were investigated. In situ measurements reveal that the transepithelial potential difference of the posterior midgut falls during the molting process. This finding was confirmed by in vitro experiments in which it was demonstrated that both the transepithelial potential and the short-circuit current are lower in molting fourth instars compared with feeding fourth instars. The short-circuit current increases after ecdysis, with a maximal rate being achieved approximately 4 h after the molt. Resumption of feeding after the molt is not necessary to initiate this increase in active ion transport. The metabolic organization of the tissue also changes during the molting process. The maximal activities of glycolytic enzymes and 3-hydroxyacyl-CoA dehydrogenase, an enzyme of lipid ss-oxidation, decrease during the molting process and increase after ecdysis. Although citrate synthase activity, an index of maximal aerobic capacity, decreases during the molt and increases again after ecdysis, tissue respiration is the same in feeding fourth instars and molting larvae. This result indicates that a greater percentage of maximal aerobic capacity is used during molting and that energy may be diverted to cell proliferation and differentiation and away from the support of active ion transport at this time.

Ion Transport Across the Midgut of the Tobacco Hornworm (Manduca Sexta)

1990 ◽  
Vol 150 (1) ◽  
pp. 425-442 ◽  
Author(s):  
M. E. CHAMBERLIN
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Tobacco Hornworm ◽  
Open Circuit ◽  
Middle Section ◽  
Anterior Section ◽  
K Secretion ◽  
K Transport ◽  
Subsequent Addition

1. The transport of K+, Na+ and Cl− across the three morphologically distinct regions of the tobacco hornworm midgut was measured under open-circuit and short-circuit conditions. Using a saline which contained physiological levels of haemolymph ions, amino acids and sugars, it was shown that all three sections actively secrete K+ and Cl− and absorb Na+. 2. The anterior section maintained the highest short-circuit current (Isc), transepithelial potential difference (PD) and net K+ secretion. The middle section had the lowest Isc, PD and K+ secretion, but absorbed Na+ at the greatest rate. The posterior section had the greatest rate of Cl− secretion. 3. Omission of K+ depressed the Isc. Subsequent addition of K+ stimulated the Isc to control levels in the middle and posterior sections, but not in the anterior section. Omission of Cl− or Na+ also inhibited the Isc. Reintroduction of Cl− had no stimulatory effect and, although reintroduction of Na+ stimulated the Isc, control levels were not attained. 4. Unlike the results reported in previous studies, the net K+ transport exceeded the Isc in all three midgut sections. The deficit in Isc was not made up by the transport of Na+ and Cl−. The results are discussed with respect to proposed models of ion transport across this epithelium.

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.

scholarly journals Barium and calcium block Bacillus thuringiensis subspecies Kurstaki delta-endotoxin inhibition of potassium current across isolated midgut of larval Manduca sexta

1988 ◽  
Vol 137 (1) ◽  
pp. 277-286 ◽  
Author(s):  
D. N. Crawford ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Manduca Sexta ◽  
Potassium Current ◽  
Short Circuit ◽  
Short Circuit Current ◽  
K Channel ◽  
Midgut Cell ◽  
Bt Toxin ◽  
Steady State Model ◽  
Delta Endotoxin

Ba2+ and Ca2+ prevent and reverse the Btk delta-endotoxin inhibition of the short-circuit current in isolated lepidopteran midgut. These findings support the K+ pump-leak steady-state model for midgut K+ homeostasis and the K+ channel mechanism of Bt toxin action. They provide a new tool with which to study the interactions between Bt toxin and midgut cell membranes.

scholarly journals Zinc inhibits cAMP-stimulated Cl secretion via basolateral K-channel blockade in rat ileum

2005 ◽  
Vol 288 (5) ◽  
pp. G956-G963 ◽  
Author(s):  
Kazi Mirajul Hoque ◽  
Vazhaikkurichi M. Rajendran ◽  
Henry J. Binder
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
K Channel ◽  
Isolated Cells ◽  
Rat Ileum ◽  
Anion Secretion ◽  
Cl Secretion ◽  
Ion Absorption ◽  
Isotonic Buffer

Zn, an essential micronutrient and second most abundant trace element in cell and tissues, reduces stool output when administered to children with acute diarrhea. The mechanism by which Zn improves diarrhea is not known but could result from stimulating Na absorption and/or inhibiting anion secretion. The aim of this study was to investigate the direct effect of Zn on intestinal epithelial ion absorption and secretion. Rat ileum was partially stripped of serosal and muscle layers, and the mucosa was mounted in lucite chambers. Potential difference and short-circuit current were measured by conventional current-voltage clamp method.86Rb efflux and uptake were assessed for serosal K channel and Na-K-2Cl cotransport activity, respectively. Efflux experiments were performed in isolated cells preloaded with86Rb in the presence of ouabain and bumetanide, whereas uptake experiments were performed in low-Cl isotonic buffer containing Ba and ouabain. Neither mucosal nor serosal Zn affected glucose-stimulated Na absorption. In contrast, forskolin-induced Cl secretion was markedly reduced by serosal but not mucosal addition of Zn. Zn also substantially reversed the increase in Cl secretion induced by 8-bromoadenosine 3′,5′-cyclic monophosphate (8-BrcAMP) with half-maximal inhibitory concentration of 0.43 mM. In contrast, serosal Zn did not alter Cl secretion stimulated by carbachol, a Ca-dependent agonist. Zn inhibited 8-BrcAMP-stimulated86Rb efflux but not carbachol-stimulated86Rb efflux. Zn had no effect on bumetanide-sensitive86Rb uptake, Na-K-ATPase, or CFTR. We conclude from these studies that Zn inhibits cAMP-induced Cl secretion by blocking basolateral membrane K channels.

A primary cation transport by a V-type ATPase of low specificity

1996 ◽  
Vol 199 (6) ◽  
pp. 1327-1334 ◽  
Author(s):  
J Küppers ◽  
I Bunse
Keyword(s):  
Ion Transport ◽  
Proton Transport ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Potential Difference ◽  
Lepidopteran Larvae ◽  
The Family ◽  
K Transport

The enzyme involved in outward K+ transport in insect epithelia belongs to the family of V-ATPases. Evidence has been reported relating the generation of the K+ gradient to a primary electrogenic proton transport via a distinct electrophoretic nH+/K+ antiport. The subject of this paper is the transport of K+ at a thread hair sensillum of the cockroach in situ. We recorded changes in the voltage and resistance of the ion-transporting membrane and of shifts in pH caused by inhibition of energy metabolism and by putative inhibitors of a proton/cation exchanger. The results are supplemented by previous determinations of the K+ activities in the same preparation. 1. In cockroach hair sensilla, the ion transport generates a membrane voltage of 105 mV. We found that the transport rendered the positive output compartment alkaline with respect to the cytoplasm by 1.0 pH unit compared with the pH at equilibrium distribution, and we infer that proton transport cannot be the process that energizes the generation of the K+ gradient. 2. The ion transport created an electrochemical potential difference for protons, DeltaetaH, of approximately 4.5 kJ mol-1, while the potential difference for K+, DeltaetaK, amounted to approximately 11 kJ mol-1. Both potential differences are directed to the cytosol. It follows from DeltaetaK/DeltaetaH that an antiport would have to be electrophoretic to drive K+ by DeltaetaH and it should, therefore, contribute to the membrane conductance. Amiloride and harmaline did not significantly change the pH in the adjacent spaces and did not affect the voltage or the resistance of the transporting membrane. Previous determinations of the impedance have shown that the ATP-independent conductance of this membrane is small, supporting the conclusion that it lacks an electrophoretic antiport. From these results, we deduce that K+ transport in cockroach sensilla is not secondary to a proton transport and an electrochemical proton gradient. The phenomena observed match the performance of a primary, electrogenic, cation-translocating ATPase of the type deduced from analyses of the short-circuit current at the midgut epithelium of lepidopteran larvae. The validity of the H+ transport/antiport hypothesis is discussed.

A double-membrane model for urinary bicarbonate secretion

1985 ◽  
Vol 249 (4) ◽  
pp. F546-F552 ◽  
Author(s):  
D. L. Stetson ◽  
R. Beauwens ◽  
J. Palmisano ◽  
P. P. Mitchell ◽  
P. R. Steinmetz
Keyword(s):  
Channel Blocker ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ultrastructural Examination ◽  
Transport Pathway ◽  
Anion Conductance ◽  
Luminal Membrane ◽  
Disulfonic Stilbene ◽  
Ph Stat

To define the transport pathway for HCO-3 secretion (JHCO3) across the apical and basolateral membranes of turtle bladder, we examined the effects of cAMP, isobutylmethylxanthine (IBMX), the Cl- channel blocker 9-anthroic acid (9-AA), and the disulfonic stilbene DIDS (4,4'-diisothiocyanostilbene-2,2'-sulfonic acid) on the electroneutral and electrogenic components of JHCO3. Total JHCO3 was measured by pH stat titration of the mucosal compartment after Na+ absorption and H+ secretion were abolished by ouabain and a delta pH, respectively. Addition of cAMP or IBMX increased total JHCO3 and induced a short-circuit current (ISC), accounting for a large part of JHCO3; net Cl- absorption was reduced. Mucosal 9-AA inhibited the IBMX-induced electrogenic component of JHCO3, whereas mucosal DIDS inhibited the electroneutral component and acetazolamide reduced both. We suggest that HCO-3 is generated within the cell by a Na-independent primary active acid-base transport at the basolateral membrane (H+ extrusion into the serosal compartment). Cellular HCO-3 accumulation drives JHCO3 via a Cl-HCO3 exchanger at the luminal membrane. IBMX and cAMP activate a 9-AA-sensitive anion conductance parallel to the exchanger. The apparent reversal of the transport elements between the two cell membranes (compared with H+-secreting cells) led to an ultrastructural examination of the carbonic anhydrase-rich cells.

Mechanism of chloride uptake in rabbit corneal epithelium

1989 ◽  
Vol 257 (2) ◽  
pp. C290-C296 ◽  
Author(s):  
J. A. Bonanno ◽  
S. D. Klyce ◽  
E. J. Cragoe
Keyword(s):  
Corneal Epithelium ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Basal Membrane ◽  
Disulfonic Acid ◽  
Chloride Uptake ◽  
Saturation Kinetics ◽  
Transport Inhibitors ◽  
Hill Coefficients ◽  
Dimethyl Amiloride

The mechanism of chloride uptake at the basal membrane (stromal side) of rabbit corneal epithelium was examined by observing the effects of ion transport inhibitors and ion concentrations on the stimulated epithelial short-circuit current (Isc). Loop diuretics inhibited the theophylline-stimulated peak and sustained Isc. Treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.2 mM) and/or 5-(N,N-dimethyl)amiloride (0.1 mM) as well as the potent anion exchange inhibitor, 5c(+)[(2,3,9,9a-tetrahydro-1H-fluoren-7-yl)oxy]acetic acid (0.01 mM), had no significant effect on Isc. These results are consistent with Cl- uptake by a Na+-Cl- or Na+-K+-2Cl- cotransport mechanism rather than Cl(-)-HCO3(-)-OH- exchange coupled to Na+-H+ exchange. Incubation in low [Na+] or [Cl-] before stimulation with forskolin (0.1 mM) reduced both peak and sustained Isc, and saturation kinetics were exhibited. Hill coefficients for [Na+] and [Cl-] were 0.99 and 1.04, respectively, for peak Isc and 0.66 and 1.18, respectively, for sustained Isc. Apparent ion affinities for Na+ and Cl- were 13.5 and 18 mM, respectively, for peak Isc and 15 and 22 mM, respectively, for sustained Isc. These results favor Cl- uptake by a 1 Na+:1 Cl- cotransport mechanism for the rabbit corneal epithelium, but involvement of K+ in this process has not been eliminated.

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