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.

scholarly journals Na+ and K+ transport at basolateral membranes of epithelial cells. I. Stoichiometry of the Na,K-ATPase.

1986 ◽  
Vol 87 (3) ◽  
pp. 467-483 ◽  
Author(s):  
T C Cox ◽  
S I Helman
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Na Transport ◽  
Basolateral Membranes ◽  
Dependent Component ◽  
Epithelial Sheets ◽  
Apical Membranes ◽  
K Transport

The stoichiometry of pump-mediated Na/K exchange was studied in isolated epithelial sheets of frog skin. 42K influx across basolateral membranes was measured with tissues in a steady state and incubated in either beakers or in chambers. The short-circuit current provided estimates of Na+ influx at the apical membranes of the cells. 42K influx of tissues bathed in Cl- or SO4-Ringer solution averaged approximately 8 microA/cm2. Ouabain inhibited 94% of the 42K influx. Furosemide was without effect on pre-ouabain-treated tissues but inhibited a ouabain-induced and Cl--dependent component of 42K influx. After taking into account the contribution of the Na+ load to the pump by way of basolateral membrane recycling of Na+, the stoichiometry was found to increase from approximately 2 to 6 as the pump-mediated Na+ transport rate increased from 10 to 70 microA/cm2. Extrapolation of the data to low rates of Na+ transport (less than 10 microA/cm2) indicated that the stoichiometry would be in the vicinity of 3:2. As pump-mediated K+ influx saturates with increasing rates of Na+ transport, Na+ efflux cannot be obligatorily coupled to K+ influx at all rates of transepithelial Na+ transport. These results are similar to those of Mullins and Brinley (1969. Journal of General Physiology. 53:504-740) in studies of the squid axon.

scholarly journals Interaction between the basolateral K+ and apical Na+ conductances in Necturus urinary bladder.

1987 ◽  
Vol 89 (4) ◽  
pp. 563-580 ◽  
Author(s):  
J R Demarest ◽  
A L Finn
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
K Channel ◽  
Channel Blockers ◽  
Na Transport ◽  
Transepithelial Na Transport ◽  
Pump Activity ◽  
Relationship Of

Experimental modulation of the apical membrane Na+ conductance or basolateral membrane Na+-K+ pump activity has been shown to result in parallel changes in the basolateral K+ conductance in a number of epithelia. To determine whether modulation of the basolateral K+ conductance would result in parallel changes in apical Na+ conductance and basolateral pump activity, Necturus urinary bladders stripped of serosal muscle and connective tissue were impaled through their basolateral membranes with microelectrodes in experiments that allowed rapid serosal solution changes. Exposure of the basolateral membrane to the K+ channel blockers Ba2+ (0.5 mM/liter), Cs+ (10 mM/liter), or Rb+ (10 mM/liter) increased the basolateral resistance (Rb) by greater than 75% in each case. The increases in Rb were accompanied simultaneously by significant increases in apical resistance (Ra) of greater than 20% and decreases in transepithelial Na+ transport. The increases in Ra, measured as slope resistances, cannot be attributed to nonlinearity of the I-V relationship of the apical membrane, since the measured cell membrane potentials with the K+ channel blockers present were not significantly different from those resulting from increasing serosal K+, a maneuver that did not affect Ra. Thus, blocking the K+ conductance causes a reduction in net Na+ transport by reducing K+ exit from the cell and simultaneously reducing Na+ entry into the cell. Close correlations between the calculated short-circuit current and the apical and basolateral conductances were preserved after the basolateral K+ conductance pathways had been blocked. Thus, the interaction between the basolateral and apical conductances revealed by blocking the basolateral K+ channels is part of a network of feedback relationships that normally serves to maintain cellular homeostasis during changes in the rate of transepithelial Na+ transport.

Transepithelial transport kinetics and Na entry in frog skin: effects of novobiocin

1976 ◽  
Vol 231 (6) ◽  
pp. 1866-1874 ◽  
Author(s):  
LJ Cruz ◽  
TU Biber
Keyword(s):  
Kinetic Parameters ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Close Correlation ◽  
Transport Kinetics ◽  
Transepithelial Transport ◽  
Linear Component ◽  
Na Transport ◽  
Transepithelial Na Transport

Na+ entry across the outer surface of frog skin and transepithelial Na transport were studied simultaneously at different [Na] in either the presence or absence of novobiocin by direct measurements of J12 (unidirectional uptake) and Io (short-circuit current). J12 consisted of two components: one linear, the other saturable. The kinetic parameters of the saturating components in controls were close to the kinetic parameters of overall transepithelial transport (Jm12 = 1.68+/-0.13 mleq cm-2h-1; Io =1.80+/-0.14 mueq cm-2h-1. K12 = 6.02+/-1.27 mM;Kio=6.12+/-1.33 mM). Novobiocin significantly augmented net transepithelial Na transport by increasing J13. J31 remained unaffected. A 1:1 relationship between the saturating component of J12 and Io was observed in both treated and untreated skins at all [Na] tested. (Jm12Iom, k12, and Kio were significantly larger in treated skins, but despite very drastic changes in transport rates, a close correlation between kinetic parameters of entry step and transepithelial transport was maintained. This suggests that the kinetics of transepithelial transport may simply reflect those of the rate-limiting step: the Na entry across the outer barrier of the skin. The results indicate that the linear component of J12 is not involved in transepithelial transport kinetics.

Active Transport of Potassium and Oxygen Consumption in the Isolated Midgut of Hyalophora Cecropia

1967 ◽  
Vol 46 (2) ◽  
pp. 235-248
Author(s):  
W. R. HARVEY ◽  
J. A. HASKELL ◽  
K. ZERAHN
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Uptake ◽  
Active Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Transport ◽  
Maximum Value ◽  
Flux Measurements ◽  
Hyalophora Cecropia ◽  
K Transport

1. Flux measurements with 42K reveal that in the isolated midgut of Hyalophora cecropia 90 to 100 % of the short-circuit current is carried by the active transport of potassium from the blood-side to the lumen. 2. When K-transport is strongly depressed, either by withholding potassium from the blood side or by imposing a large positive potential on the lumen, the oxygen uptake of the isolated gut remains virtually unchanged. If the K-transport were to be energized by the negligible increase in oxygen uptake about 40 µ-equiv. of potassium would have to be transported for every µ-equiv. of extra oxygen taken up. This ratio of K-transport to oxygen uptake is thermodynamically impossible. 3. The ratio of potassium transported to total oxygen consumed when the midgut is bathed with 32 mM potassium on both sides is about 1.3 at temperatures of 25° and 15° C. The ratio must be smaller at lower potassium concentrations and is 2.0 at 73.5 mM-K, which may be approaching the maximum value. 4. Although the oxygen uptake is independent of the K-transport, the reverse is not true. There is a close dependency of K-transport on oxygen consumption. 5. K-transport by the midgut contrasts with Na-transport by the frog skin because Na-transport stimulates oxidative metabolism whereas K-transport does not. Evidently the coupling of transport to energy supply is different in the two systems.

scholarly journals Na+ and K+ transport at basolateral membranes of epithelial cells. III. Voltage independence of basolateral membrane Na+ efflux.

1986 ◽  
Vol 87 (3) ◽  
pp. 503-509 ◽  
Author(s):  
T C Cox ◽  
S I Helman
Keyword(s):  
Frog Skin ◽  
Basolateral Membrane ◽  
Pump Current ◽  
Voltage Sensitivity ◽  
Na Transport ◽  
Previous Suggestion ◽  
Basolateral Membranes ◽  
Transmembrane Voltage ◽  
Na Efflux ◽  
K Transport

Na+ efflux across basolateral membranes of isolated epithelia of frog skin was tested for voltage sensitivity. The intracellular Na+ transport pool was loaded with 24Na from the apical solution and the rate of isotope appearance in the basolateral solution (JNa23) was measured at timed intervals of 30 s. Basolateral membrane voltage was depolarized by either 50 mM K+, 5 mM Ba++, or 80 mM NH+4. Whereas within 30 s ouabain caused inhibition of JNa23, depolarization of Vb by 30-60 mV caused no significant change of JNa23. Thus, both pump-mediated and leak Na+ effluxes were voltage independent. Although the pumps are electrogenic, pump-mediated Na+ efflux is voltage independent, perhaps because of a nonlinear relationship between pump current and transmembrane voltage. Voltage independence of the leak Na+ efflux confirms a previous suggestion (Cox and Helman, 1983. American Journal of Physiology. 245:F312-F321) that basolateral membrane Na+ leak fluxes are electroneutral.

Chloride dependence of the HCO3 exit step in urinary acidification by the turtle bladder

1983 ◽  
Vol 245 (5) ◽  
pp. F564-F568
Author(s):  
J. L. Fischer ◽  
R. F. Husted ◽  
P. R. Steinmetz
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Methyl Sulfate ◽  
Na Transport ◽  
Secreting Cell ◽  
High Affinity ◽  
Turtle Bladder ◽  
Normal Ringer

To characterize the efflux of HCO-3 across the basolateral membrane of the H+-secreting cells of the turtle bladder, we examined the effect of substitution of gluconate or methyl sulfate for Cl- on the rate of acidification (JH). JH was measured as the short-circuit current in bladders in which Na+ transport was abolished with 10(-4) M ouabain. In hemibladders bathed in normal Ringer solution (Cl- = 122 mM) JH was 44.9 microA. Substitution of the Cl- resulted in a marked reduction in JH (12.5 microA with gluconate and 7.5 microA with methyl sulfate). Addition of Cl- to the mucosal surface had no effect on JH. In contrast, serosal addition of Cl- restored JH to control. The apparent Km for Cl- in gluconate Ringer was 0.13 mM. Serosal furosemide (1 mM) inhibited JH by 55% in Cl- Ringer. We conclude that HCO-3 exit across the basolateral membrane of the H+-secreting cell occurs via a Cl-HCO3 exchanger that has a high affinity for chloride.

Complex response of epithelial cells to inhibition of Na+ transport by amiloride

1988 ◽  
Vol 254 (2) ◽  
pp. C297-C303 ◽  
Author(s):  
R. S. Fisher ◽  
J. W. Lockard
Keyword(s):  
Urinary Bladder ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Second Phase ◽  
Toad Urinary Bladder ◽  
Apical Surface ◽  
Na Transport ◽  
Transport Inhibition

When toad urinary bladder or frog skin epithelia are treated with amiloride, short-circuit current (Isc), which represents the net active transepithelial Na+ transport rate from the apical to basolateral surface, decreases rapidly (2-5 s) to approximately 15-20% of control values and then slowly, over several minutes, continues falling toward zero. The contribution of this second phase of the decline is dependent on the transporting condition of the tissue before administration of amiloride. Attenuation of the second phase was observed if tissues were subjected to a period of transport inhibition. Tissues preincubated in 0 Na+ Ringer solution on the apical surface were returned to control Na+ Ringer, which caused an approximately 25% increase of Isc above control values. Immediate reapplication of amiloride caused Isc to decrease more rapidly than the previous exposure to values near zero, substantially reducing or eliminating the secondary slow decline. After long-term reincubation of tissues in control, 100 mM Na+ solution, another treatment with amiloride indicated that the magnitude of the secondary decline increased in frog skin but not in urinary bladder epithelia. We conclude that the effect of amiloride is complex and may cause additional effects besides simply blocking entry of Na+ into the apical membrane channel, and we suggest that regulatory mechanisms may be invoked in response to transport inhibition.

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.

scholarly journals Ouabain on active transepithelial sodium transport in frog skin: studies with microelectrodes.

1979 ◽  
Vol 74 (1) ◽  
pp. 105-127 ◽  
Author(s):  
S I Helman ◽  
W Nagel ◽  
R S Fisher
Keyword(s):  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Equilibrium Potential ◽  
Electrical Model ◽  
Na Transport ◽  
Rapid Phase ◽  
Transepithelial Na Transport ◽  
Transepithelial Voltage ◽  
Transepithelial Sodium Transport

Studies were done with isolated frog skin to determine the effects of 10(-4) M ouabain on the electrophysiological parameters of outer and inner barriers of the Na-transporting cells. Microelectrodes were used to impale the skins from the outer surface to determine the intracellular voltages (Vsco) under conditions of short-circuiting and under conditions where a voltage clamp was used to vary the transepithelial voltage, VT. From this, the electrical resistances of outer (Rfo) and inner (RI) barriers were estimated. In addition, the driving force for active transepithelial Na transport (ENa = E'1) was estimated from the values of VT when the Vo = 0 mV (Helman and Fisher. 1977. J. Gen. Physiol. 69: 571-604). Studies were done with skins bathed with the usual 2.4 meq/liter [K]i in the inner solution as well as with reduced [K]i of 0.5 and 0 meq/liter. Characteristically, the responses to ouabain could be described by an initial rapid phase (5-10 min) during which time the Ri was increased markedly and the E'1 was decreased from control values. Thereafter, during the slow phases of the response, the resistances of both outer and inner barriers increased continuously and markedly with time leading ultimately to essentially complete inhibition of the short-circuit current. Similar studies were done with skins exposed to 10(-4) M amiloride in the outer solution. Although estimates of Ri could not be obtained under these conditions, the effects on the Vsco and E'1 were similar to those observed for the Na-transporting skins. However, the magnitudes of the effects were less and relatively slower than observed for the Na-transporting skins. The results of these studies were analyzed within the context of a proposed electrical model that takes into account the observation that the magnitude of the voltage at the inner barrier appears to exceed the equilibrium potential for K especially when transepithelial Na transport is inhibited at the apical barrier of the cells.

Effect of K channel blockers on basal and β-agonist stimulated ion transport by fetal distal lung epithelium

1993 ◽  
Vol 71 (1) ◽  
pp. 54-57 ◽  
Author(s):  
Hugh O'Brodovich ◽  
Bijan Rafii
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Alveolar Epithelium ◽  
Short Circuit Current ◽  
K Channel ◽  
Channel Blockers ◽  
Lung Epithelium ◽  
Na Transport ◽  
Ussing Chambers ◽  
Distal Lung

To determine whether basolateral K channels play an important role in the basal and β-agonist stimulated ion transport by fetal distal lung epithelium we harvested these cells from fetal rats (20 days gestation, term = 22 days) and studied them in Ussing chambers. Short-circuit current (Isc) fell with basal 3 mM BaCl2 (3.0 ± 0.2 (±SEM) to 2.0 ± 0.2 μA∙cm−2, n = 18, p < 0.01) without affecting monolayer resistance (R = 693 ± 57 Ω∙cm2). Basal quinine sulfate (1 mM) also decreased Isc (3.7 ± 0.15 to 3.0 ± 0.10 μA∙cm−2; n = 4, p < 0.01). None of apical BaCl2 (3 mM), apical quinine (1 mM), nor bilaterally applied tetraethylammonium (10 mM), lidocaine (1 mM), or 4-aminopyridine (2 mM) decreased Isc. Cell monolayers treated with basal BaCl2 (3 mM) demonstrated an impaired ability to increase their Isc in response to the β2-agonist terbutaline (1 mM). Basal 3 mM BaCl2 also decreased Isc in amiloride (0.1 mM) and furosemide (1 mM) treated monolayers, indicating that barium also affected the previously described amiloride-insensitive Na transport by these cells (n = 8, p < 0.01). Together these experiments suggest that normal basolateral K channel function is required for normal and β2-stimulated Na transport in fetal distal lung epithelium.Key words: type II alveolar epithelium, potassium channels, β-agonist, sodium transport, Na channels.

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