scholarly journals Further Observations on the Regulation of KCl ABSORPTION ACROSS LOCUST RECTUM

1985 ◽  
Vol 116 (1) ◽  
pp. 153-167
Author(s):  
J. W. HANRAHAN ◽  
J. E. PHILLIPS
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Open Circuit ◽  
High K ◽  
K Concentration ◽  
K Permeability

1. Electrophysiological and tracer flux techniques were used to studyregulation of KC1 reabsorption across locust recta. Physiologically high K+levels (100 mmolI−1) on the lumen side stimulated net 36Cl flux and reduced the theoretical energy cost of anion transport under open-circuit conductions. 2. The stimulation of short-circuit current (Ibc i.e. active C− absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Ibc were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl− absorption and counter-ion (K+) permeability. 3. High mucosal osmolarity or K+ concentration decreased Ibc and caused a disproportionately large increase in Rt, consistent with a decrease in theshunt (K+) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K+ levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo atthe end of resorptive cycles also inhibited Ibc, apparently without affecting K+ permeability.

Calcium secretion in canine tracheal mucosa

1985 ◽  
Vol 59 (4) ◽  
pp. 1191-1195 ◽  
Author(s):  
F. J. Al-Bazzaz ◽  
T. Jayaram
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Potential Difference ◽  
Secretory Process ◽  
Metabolic Inhibitor ◽  
Tracheal Mucosa ◽  
Transepithelial Potential ◽  
Transepithelial Potential Difference

Calcium (Ca) affects many cellular functions of the respiratory tract mucosa and might alter the viscoelastic properties of mucus. To evaluate Ca homeostasis in a respiratory epithelium we investigated transport of Ca by the canine tracheal mucosa. Mucosal tissues were mounted in Ussing-type chambers and bathed with Krebs-Henseleit solution at 37 degrees C. Unidirectional fluxes of 45Ca were determined in tissues that were matched by conductance and short-circuit current (SCC). Under short-circuit conditions there was a significant net Ca secretion of 1.82 +/- 0.36 neq . cm-2 . h-1 (mean +/- SE). Under open-circuit conditions, where the spontaneous transepithelial potential difference could attract Ca toward the lumen, net Ca secretion increased significantly to 4.40 +/- 1.14 compared with 1.54 +/- 1.17 neq . cm-2 . h-1 when the preparation was short-circuited. Addition of a metabolic inhibitor, 2,4-dinitrophenol (2 mM in the mucosal bath), decreased tissue conductance and SCC and slightly decreased the unidirectional movement of Ca from submucosa to lumen. Submucosal epinephrine (10 microM) significantly enhanced Ca secretion by 2.0 +/- 0.63 neq . cm-2 . h-1. Submucosal ouabain (0.1 mM) failed to inhibit Ca secretion. The data suggest that canine tracheal mucosa secretes Ca; this secretory process is augmented by epinephrine or by the presence of a transepithelial potential difference as found under in vivo conditions.

Sch-28080 inhibits bafilomycin-sensitive H+ secretion in turtle bladder independently of luminal [K+]

1993 ◽  
Vol 265 (2) ◽  
pp. F174-F179
Author(s):  
O. F. Kohn ◽  
P. P. Mitchell ◽  
P. R. Steinmetz
Keyword(s):  
Competitive Inhibition ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Atpase Inhibitor ◽  
Turtle Bladder ◽  
High K ◽  
Ph Stat ◽  
Low Levels ◽  
K Concentration ◽  
Removal Studies

To explore the possible contribution of an H-K-adenosine-triphosphatase (H-K-ATPase) to H+ secretion (JH) in the isolated turtle bladder, we measured electrogenic JH (JeH) as short-circuit current and total JH (JTH) by pH stat titration in the presence of ouabain at different ambient K+ concentration ([K+]) and during luminal addition of a known gastric H-K-ATPase inhibitor, Schering (Sch)-28080. JH was not reduced by decreasing ambient [K+] to undetectable or very low levels (< 0.05 mM by atomic absorption) and luminal BaCl2 addition to further reduce local [K+] at the apical membrane. These K(+)-removal studies indicate that H+ transport is not coupled to countertransport of K+. JTH did not exceed JeH at any point: in K(+)-free solutions JTH was 0.73 +/- 0.05, and JeH was 0.95 +/- 0.08 mumol/h; in standard (3.5 mM) K+ solutions JTH was 0.72 +/- 0.05 and JeH 0.98 +/- 0.06 mumol/h; in high (118 mM) K+ solutions JTH was 0.65 +/- 0.07 and JeH 0.94 +/- 0.08 mumol/h. Sch-28080 caused a rapid inhibition of JH, with similar half-maximal inhibitory concentrations (IC50) in K(+)-free, standard [K+], and high [K+] solutions. Bafilomycin inhibited JeH and JTH with an IC50 of approximately 100 nM. The observed non-potassium-competitive inhibition of JH by Sch-28080 and the bafilomycin sensitivity distinguish the H-ATPase of the turtle bladder from the gastric H-K-ATPase. The rapidity of the inhibition by Sch-28080 suggests that it acts at an accessible luminal site of the ATPase.

Intestinal ion transport in rats with spontaneous arterial hypertension

1988 ◽  
Vol 75 (2) ◽  
pp. 127-133 ◽  
Author(s):  
Ralf Lübcke ◽  
Gilbert O. Barbezat
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Chloride Secretion ◽  
Sodium Absorption ◽  
Spontaneously Hypertensive ◽  
Wistar Kyoto ◽  
Intestinal Ion Transport

1. Ion balance, intestinal ion transport in vivo with luminal Ringer, and direct voltage clamping in vivo with luminal Ringer and sodium-free choline-Ringer were studied in young (40 days old) and adult (120 days old) spontaneously hypertensive rats (SHR) and age-matched normotensive controls (Wistar–Kyoto rats, WKY). 2. Faecal sodium output was significantly higher in SHR compared with WKY in both young (+ 67%) and adult (+ 43%) rats. 3. Small-intestinal sodium absorption was equal in young SHR and WKY, but significantly greater net sodium absorption was found in the ileum of adult SHR. In contrast, net sodium absorption was reduced from the colon of both young and adult SHR. 4. In adult SHR, the colonic transepithelial short-circuit current (Isc) and the transepithelial potential difference (PD) were significantly higher, whereas the transepithelial membrane resistance (Rm) was significantly lower than in WKY. There was an identical drop in Isc in both strains when luminal sodium was replaced by choline. These data cannot be explained by increased electrogenic cation (sodium) absorption in the SHR, but would favour chloride secretion. 5. It is suggested that in SHR membrane electrolyte transport abnormalities may also be present in the epithelial cells of the small and large intestine, as have been demonstrated already in blood cells by several investigators. The SHR may become an interesting experimental animal model for the study of generalized ion transport disorders.

scholarly journals THE INHIBITORY EFFECT OF STROPHANTHIDIN ON SECRETION BY THE ISOLATED GASTRIC MUCOSA

1959 ◽  
Vol 42 (6) ◽  
pp. 1233-1239 ◽  
Author(s):  
I. L. Cooperstein
Keyword(s):  
Gastric Mucosa ◽  
Chloride Transport ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Inhibitory Effect ◽  
Transport Systems ◽  
Anion Secretion ◽  
Diffusion Component ◽  
Sodium And Potassium

The unidirectional fluxes of Na+ and Cl- were measured across the isolated gastric mucosa of the bullfrog (R. catesbiana). The addition of strophanthidin, a cardiac aglycone, resulted in marked reductions of the spontaneous potential and short-circuit current. Associated with these changes, the isolated gastric mucosa ceased secreting chloride and hydrogen ion. Although the active component of chloride transfer was inhibited, the exchange diffusion component seemed to increase. No significant changes in membrane conductance or sodium flux were noted. Possible mechanisms of strophanthidin inhibition were discussed in view of its effect on chloride transport across the gastric mucosa and on sodium and potassium transfer in other tissues. It was concluded that the cardiac glycosides may not be specific inhibitors of sodium and potassium transport. This non-specific inhibition suggests that active chloride transport is affected by strophanthidin directly and/or anion secretion is dependent upon normal functioning of cation transport systems in the tissue.

Studies on locust rectum. III. Stimulation of electrogenic chloride transport by hemolymph

1980 ◽  
Vol 58 (10) ◽  
pp. 1933-1939 ◽  
Author(s):  
J. H. Spring ◽  
J. E. Phillips
Keyword(s):  
Steady State ◽  
Filter Paper ◽  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Simultaneous Measurements ◽  
Parallel Increase ◽  
Neuroendocrine Organ ◽  
Stimulation Of

Hemolymph was collected from recently fed desert locusts either by adsorption onto filter paper, or by centrifugation and methanol extraction. Whole hemolymph caused both the short-circuit current (Isc) and open-circuit transepithelial electropotential difference (PD) across locust recta mounted in Ussing-type chambers to double during the steady-state period. Methanol extracts of hemolymph caused similar but smaller increases in Isc. The transepithelial resistance (R) did not change. Simultaneous measurements of 36Cl− fluxes indicated that all of the increase in Isc following stimulation could be accounted for by a parallel increase in net Cl− absorption from the lumen side. With the exception of an initial small biphasic fluctuation in Isc, stimulation by hemolymph exhibited identical characteristics to those produced by submaximal dosages of corpora cardiaca (CC). Cardiatectomy drastically reduced the stimulatory activity of hemolymph, suggesting that this neuroendocrine organ is the source of the active factor (chloride transport stimulating hormone (CTSH)) in hemolymph.

scholarly journals Cellular mechanisms and control of KCl absorption in insect hindgut

1983 ◽  
Vol 106 (1) ◽  
pp. 71-89 ◽  
Author(s):  
J. W. Hanrahan ◽  
J. E. Phillips
Keyword(s):  
Cyclic Amp ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Basal Membrane ◽  
Peptide Hormone ◽  
Open Circuit ◽  
Electrochemical Gradient ◽  
Cellular Mechanisms

The hindgut of the desert locust possesses an unusual chloride transport system. The isolated locust rectum absorbs chloride from the mucosal (lumen) to the serosal (haemolymph) side at a rate which is equal to the short-circuit current (Isc). Net chloride transport (JClnet) persists in nominally Na-free or HCO3(CO2)-free saline, is insensitive to normal inhibitors of NaCl co-transport and anion exchange, and is independent of the net electrochemical gradient for sodium across the apical membrane. However, active chloride transport is strongly dependent on mucosal potassium (Ka = 5.3 mM-K). Chloride entry across the apical membrane is active, whereas the net electrochemical gradient across the apical membrane is active, whereas the net electrochemical gradient across the basal membrane favours passive Cl exit from the cell. Although mucosal potassium directly stimulates ‘uphill’ chloride entry, there is no evidence for coupled KCl co-transport, nor would co-entry with potassium be advantageous energetically. Net chloride absorption and Isc are stimulated by a peptide hormone from the central nervous system which acts via cyclic-AMP. Cyclic-AMP increases Isc and JClnet approximately 1000% and transepithelial conductance (Gt) approximately 100%. Approximately half of the delta Gt during stimulation results from increased Cl conductance at the basal cell border. This increase is also reflected in a shift of the basal membrane e.m.f. towards the Nernst potential for chloride. The remainder of the cAMP-induced delta Gt is due to an elevation of apical membrane K conductance, which causes a 400% increase in transepithelial potassium permeability as estimated by radiotracer diffusion. Because of this stimulation of K conductance, potassium serves as the principal counterion for active chloride transport under open-circuit conditions. Very high luminal levels of K oppose the stimulatory actions of cAMP on active Cl transport and K conductance. These and other results have been incorporated into a cellular model for KCl absorption across this insect epithelium.

Role of active potassium transport by integumentary epithelium in secretion of larval-pupal moulting fluid during silkmoth development

1975 ◽  
Vol 62 (2) ◽  
pp. 357-366
Author(s):  
A. M. Jungreis ◽  
W. R. Harvey
Keyword(s):  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Open Circuit ◽  
Ratio Test ◽  
Potassium Flux

1. The exuvial side of the pharate pupal integument is usually positive to the haemolymph-side, both in vivo and in vitro, during the period when the moulting fluid is being secreted. 2. The ratio of potassium flux toward the exuvial space is higher than that toward the haemolymph, under both open-circuit conditions and short-circuit conditions, demonstrating by the Flux Ratio test that potassium is actively transported across the isolated integument during this secretion period. 3. Just prior to ecdysis, while moulting fluid is being reabsorbed, the potassium flux ratios become unity, suggesting that active potassium transport has ceased, but the short-circuit current that remains suggests that some other ion is actively transported at this time. 4. We argue that the potassium salt solution, formed in the exuvial space (as water presumably follows the actively transported potassium), has three functions (1) to accomplish the gel--sol transformation, (2) to activate the gel enzymes and (3) to buffer the enzyme solution at a pH favourable to the activity of the gel enzymes.

Sodium and chloride transport in the isolated intestine of the earthworm, Lumbricus terrestris (L.)

1982 ◽  
Vol 97 (1) ◽  
pp. 197-216
Author(s):  
J. C. Cornell
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Lumbricus Terrestris ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Ionic Basis ◽  
Good Agreement

1. Measurements of electrical potential difference (PD), short-circuit current (SCC) and unidirectional fluxes of sodium and chloride were made across portions of the intestine. Based on the results, the intestine can be divided into at least four physiologically distinct regions. 2. These four physiological regions, designated from anterior to posterior as R I-II, R III A, R III B and R IV, do not completely correspond to the four anatomically distinct regions of the intestine. 3. The PD (serosal side positive) in R I-II, R III A, R III B and R IV is 1.08, 12.4, 5.61 and 31.7 mV, respectively. 4. The SCC in these same regions is 9.9, 50.4, 49.7, and 16.4 micro A cm2, respectively. 5. When short-circuited, net sodium and net chloride fluxes in the above regions are −0.36 and −0.27, 1.46*** and −0.92*, 1.74*** and −0.06 and 1.01*** and 0.07 mumol cm-2 h-1, respectively. Positive fluxes indicate net mucosal to serosal movements and asterisks indicate significant net fluxes (* P less than 0.05, *** P less than 0.001). 6. There is good agreement between the SCC and net sodium transport in R III B. In the other regions of the intestine the ionic basis of the SCC has not been completely explained. 7. The properties of the intestine in vitro appear to make the intestine well suited for the task of conserving sodium, a function which the intestine performs in vivo.

Hormonal control of chloride transport across locust rectum

1978 ◽  
Vol 56 (8) ◽  
pp. 1879-1882 ◽  
Author(s):  
J. Spring ◽  
J. Hanrahan ◽  
J. Phillips
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Fold Increase ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Hormonal Control ◽  
Net Flux ◽  
Hemolymph Volume ◽  
Camp Levels

Rates of ion transport across locust recta were monitored in vitro by following fluxes of 22Na+ and 36Cl−, short-circuit current (Isc), and open-circuit electropotential difference (PD) across this epithelium for several hours. Corpora cardiaca (CC) homogenates, cAMP, theophylline, and hemolymph of recently fed locusts all stimulate electrogenic transport of Cl− across locust rectum, as indicated by a two- to three-fold increase in 36Cl− net flux, Isc, and PD. Cyclic AMP caused a Cl-dependent increase in PD across the lumen-facing but not the hemocoel-facing plasma membrane of the epithelial cells. We propose that a blood-borne factor, possibly from the CC, causes an elevation in cAMP levels in rectal tissue and that this second messenger acts by increasing Cl− entry into the cell from the rectal lumen. Additional fluid absorption accompanies the resulting increase in transport of NaCl, leading to an increase in the hemolymph volume of previously dehydrated locusts.

Determination of short-circuit current in the in vivo perfused rat colon

1984 ◽  
Vol 246 (2) ◽  
pp. G151-G158 ◽  
Author(s):  
H. Knauf ◽  
K. Haag ◽  
R. Lubcke ◽  
E. Berger ◽  
W. Gerok
Keyword(s):  
Specific Resistance ◽  
Short Circuit ◽  
Input Resistance ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Open Circuit ◽  
Rat Colon ◽  
Length Constant

Current pulses (I) were injected into the lumen of proximal colonic segments in vivo, and the corresponding voltage deflections (delta PD) superimposed on the transcolonic PD were recorded. From the exponential decay of delta PD along the colon axis, the electrical length constant (lambda) was determined. Based on cable analysis the input resistance (= delta PD x = 0/I) and lambda made it possible to calculate the specific resistance (Rm) of the colonic epithelium as 128 +/- 16 omega X cm2. As Rm proved to be an ohmic resistor, the extrapolation from open-circuit PD (8-12 mV, lumen negative) to zero PD was feasible and made the calculation of short-circuit current (= PD/Rm) equal to 70 +/- 16 microA/cm2. In the presence of amiloride short-circuit current decreased to about 50%, whereas with theophylline it increased by about 30%. Substitution of luminal Na+ with choline or Cl- with cyclamate was associated with a marked increase of Rm. The rheogenic component of net Na+ transport was estimated to be only 8%. Electroneutral Na+ absorption functionally coupled with Cl- absorption displayed the characteristic feature of ion transport in the rat proximal colon.

Sign in / Sign up

Export Citation Format

Share Document