scholarly journals Na Transport across Frog Skin at Low External Na Concentrations

1966 ◽  
Vol 49 (6) ◽  
pp. 1161-1176 ◽  
Author(s):  
THOMAS U. L. BIBER ◽  
RONALD A. CHEZ ◽  
PETER F. CURRAN
Keyword(s):  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Potential Profile ◽  
Na Transport ◽  
Ringer’S Solution ◽  
Electrical Potentials ◽  
Single Compartment

Isolated frog skin was bathed with a dilute solution containing 1 mm NaCl on the outside and with normal Ringer’s solution on the inner surface. Net Na flux was determined by simultaneous measurement of unidirectional fluxes with Na22 and Na24 and intracellular electrical potentials were examined with microelectrodes. There was a net inward transport of Na under both open-circuit and short-circuit conditions. The short-circuit current was approximately 15% greater than the net Na flux; the discrepancy could be accounted for by a small outward flux of Cl. The electrical potential profile did not differ greatly from that observed in skins bathed on the outside with normal Ringer’s solution. Under open-circuit conditions, there were usually several potential steps and under short-circuit conditions the cells were negative relative to the bathing solutions. Estimates of epithelial Na concentrations utilizing radioactive Na suggested that if all epithelial Na were in a single compartment, an active entry step would be necessary to allow a net inward Na transport. The results could also be explained by a series arrangement of Na compartments without necessarily postulating an active Na entry. The behavior of the potential profile suggested that this latter alternative was more likely.

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.

Effect of furosemide on the electrical parameters of frog skin

1982 ◽  
Vol 243 (6) ◽  
pp. F581-F587 ◽  
Author(s):  
A. Corcia ◽  
S. R. Caplan
Keyword(s):  
Active Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Relative Increase ◽  
Electrical Potential Difference ◽  
Electrical Parameters ◽  
Active Conductance ◽  
Solution Bathing

When added to the mucosal solution bathing isolated frog skin at concentrations ranging from 5 X 10(-4) to 3 X 10(-3) M, the diuretic furosemide increased both the active transport of sodium and the electrical potential difference across the tissue in a dose-dependent way. The same effect was observed in chloride-free solutions. Mucosal furosemide also decreased the passive unidirectional fluxes of chloride. We believe that as far as electrical parameters are concerned mucosal furosemide has a double effect in frog skin: it increases the active conductance to sodium across the mucosal membrane, thus increasing active transport, and decreases the passive permeability to chloride, thus altering the passive conductance of the skin. The relative increase in short-circuit current was, however, invariably greater than the increase of the active conductance, suggesting the influence of yet a third effect. The effect of mucosal furosemide on active sodium transport was blocked by amiloride (5 X 1-(-5) M) and was independent of vasopressin. Qualitatively the effect was similar to the effect produced by triphenylmethylphosphonium ion.

Electrical and transport characteristics of skin of larval Rana catesbeiana

1979 ◽  
Vol 237 (1) ◽  
pp. R74-R79 ◽  
Author(s):  
T. C. Cox ◽  
R. H. Alvarado
Keyword(s):  
Rana Catesbeiana ◽  
Short Circuit ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Open Circuit ◽  
Shunt Resistance ◽  
Ion Substitution ◽  
Adult Skin

Carefully dissected, mounted, and bathed with Ringer solution, the larval bullfrog skin has a resistance of about 9,000 omega.cm2 and a stable transepithelial electrical potential of about 20 mV (inside +). A short-circuit current of about 2 microA.cm-2 is generated that is comparable in magnitude to the net inward flux of Na+. At open circuit the flux ratio equation for Na+ is not satisfied. Larval skin is less sensitive to ouabain, amiloride, and ADH than adult skin. The current-voltage (C-V) relationship across the preparation is not linear; there are distinct breaks in both the hyperpolarizing and hypopolarizing regions. The former break, at about +130 mV, corresponds with a break observed in adult skin that corresponds with ENa. The shunt resistance (RS) and active pathway resistance (RA) were estimated by C-V curve analysis and by ion substitution. The two methods yielded comparable values with RS about 11 k omega.cm2 and RA about 62 k omega.cm2. It is suggested that transport is limited by the number of entry sites for sodium at the apical border of transport cells.

In vitro studies of sodium transport across the lower intestine of a desert parrot

1980 ◽  
Vol 239 (3) ◽  
pp. R285-R290
Author(s):  
E. Skadhauge ◽  
T. J. Dawson
Keyword(s):  
Short Circuit ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Na Transport ◽  
Salt Loading ◽  
Ussing Chambers ◽  
Lower Intestine

The lower intestine (coprodeum and colon) of the Australian parrot, the galah, was mounted in Ussing chambers. Short-circuit current (SCC), electrical potential difference (PD), and unidirectional fluxes of Na and Cl were measured in birds that were fed mixed seeds or were NaCl loaded. The net Na transport of both coprodeum and colon was nearly equal to the SCC, and the flux ratio for Cl was unity. In birds which received mixed seeds, average coprodeal Na transport was 7.8 mu eq . cm-2 . h-1, and PD was 19 mV. The Km for Na was 5.7 meq/l. In colon, Na transport was reduced by 67% and PD by 70%. The ratio between unidirectional Na and Cl fluxes in the serosa-mucosa direction was 0.7. Salt loading suppressed coprodeal, but increased colonic Na transport. The coprodeal and colonic SCC and NA transport of birds receiving mixed seeds were inhibited by amiloride on the mucosal side. Colonic SCC of NaCl-loaded birds was only slightly reduced by amiloride (by 17%), but stimulated by amino acids (by 18%).

Na+ transport and pH in principal cells of frog skin: effect of antidiuretic hormone

1994 ◽  
Vol 267 (1) ◽  
pp. R107-R114
Author(s):  
V. Lyall ◽  
T. S. Belcher ◽  
J. H. Miller ◽  
T. U. Biber
Keyword(s):  
Antidiuretic Hormone ◽  
Frog Skin ◽  
Apical Membrane ◽  
Short Circuit ◽  
Apical Cell ◽  
Short Circuit Current ◽  
Arginine Vasotocin ◽  
Na Transport ◽  
Apical Cell Membrane ◽  
Principal Cells

Intracellular pH (pHi), apical membrane potential (Va), and fractional apical membrane resistance (FRa) were measured in principal cells of isolated frog skin (Rana pipiens) with double-barreled microelectrodes under short-circuit conditions. Basolateral exposure to 10 mU/ml arginine vasotocin (AVT) depolarized Va by 30 mV, decreased FRa by 33%, increased short-circuit current (Isc) by 17 microA, and increased pHi by 0.17 pH units. The response of Va, Isc, and pHi occurred concurrently. Forskolin, theophylline, and 8-(4-chlorophenyl-thio)-adenosine 3',5'-cyclic monophosphate caused similar changes in Va, Isc, and pHi. The enhanced response of Isc, Va, and FRa to short pulses of apical amiloride applied during AVT or cAMP exposure suggests an increase in apical Na+ conductance. The presence of cAMP agonists also enhanced the response of pHi to amiloride. We conclude that the AVT- and cAMP-induced increase in Na+ transport across the apical cell membrane is associated with a change in pHi. These data are consistent with the hypothesis that changes in pHi may play a role in the second messenger cascade initiated by the antidiuretic hormone.

scholarly journals THE EFFECTS OF MAGNESIUM ON NUCLEOSIDE PHOSPHATASE ACTIVITY IN FROG SKIN

1967 ◽  
Vol 33 (2) ◽  
pp. 411-418 ◽  
Author(s):  
Rolf H. Dahl ◽  
James N. Pratley
Keyword(s):  
Cell Membrane ◽  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Spectrophotometric Analysis ◽  
Electrical Potential Difference ◽  
Ion Pump ◽  
Pump System ◽  
Nucleoside Triphosphatase

Histochemical tests, employing the Wachstein-Meisel medium, indicate that nucleoside triphosphatase activity is found predominantly in two areas of the frog skin epidermis: (1) in mitochondria, where activity is enhanced by dinitrophenol, Mg2+ dependent, but inhibited by fixation; and (2) apparently associated with cell membranes of the middle and outer portions of the epidermis, where activity is inhibited by Mg2+, unaffected by dinitrophenol, and only slightly reduced by fixation. Spectrophotometric analysis shows that Mg2+ in the medium does not increase spontaneous hydrolysis of ATP, thus obviating the possible explanation that changes in substrate concentrations in the medium lead to alterations in the "staining" distributions. It is postulated that perhaps the two enzymes differ in their requirements for substrate—one requiring the polyphosphate to be in complexed form with Mg2+, the other uncomplexed. Concentrations of Mg2+ required to inhibit cell membrane nucleoside triphosphatase activity also inhibit the electrical potential difference and short-circuit current of the frog skin. Although these observations might be taken as presumptive evidence of the cell membrane enzyme as a component of the ion pump system, because of certain dissimilarities with respect to the biochemists' "transport ATPase" and for other reasons discussed in the paper, any definite conclusions in this regard are premature.

Network thermodynamic modeling of hormone regulation of active Na+ transport in cultured renal epithelium (A6)

1986 ◽  
Vol 250 (6) ◽  
pp. C978-C991 ◽  
Author(s):  
M. L. Fidelman ◽  
D. C. Mikulecky
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Hormone Regulation ◽  
Na Channels ◽  
Na Transport ◽  
Renal Epithelium ◽  
Ion Concentrations ◽  
Tight Junction Permeability

A network thermodynamic model was developed to describe steady-state ion flows (Na+,K+, and Cl-) and related electrical events in a cultured renal epithelium (A6) derived from toad kidney. Three hypotheses for explaining the steady-state increases in short-circuit current (SCC) produced by aldosterone and/or insulin were examined using the model. Changing only the number of basolateral Na+-K+ pumps produced virtually no change in SCC and was ruled out. Changing only the number of apical Na+ channels could produce sufficient increases in SCC but presented problems in the pattern of changes produced in cell ion concentrations and therefore appeared unlikely. Changing both apical and basolateral parameters in a balanced, coordinated manner produced the maximal changes in SCC with the minimal changes in cell ion concentrations and appeared to be the "best" hypothesis. In addition, it was found necessary for tight junction permeability to increase as active Na+ transport increased under open-circuit conditions. Simulations, using these results, compared favorably with experimental data on the stimulatory effects of aldosterone and insulin, both separately and together, on active Na+ transport.

scholarly journals Energetics of Sodium Transport in Frog Skin

1972 ◽  
Vol 59 (1) ◽  
pp. 77-91 ◽  
Author(s):  
F. L. Vieira ◽  
S. R. Caplan ◽  
A. Essig
Keyword(s):  
Free Energy ◽  
Oxygen Consumption ◽  
Sodium Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Rate Of Oxygen Consumption ◽  
Phenomenological Coefficients

Studies were made of the dependence of the rate of oxygen consumption, Jr, on the electrical potential difference, Δψ, across the frog skin. After the abolition of sodium transport by ouabain the basal oxygen consumption was independent of Δψ. In fresh skins Jr was a linear function of Δψ over a range of at least ±70 mv. Treatment with aldosterone stimulated the short-circuit current, Io, and the associated rate of oxygen consumption, Jro, and increased their stability; linearity was then demonstrable over a range of ±160 mv. Brief perturbations of Δψ (±30–200 mv) did not alter subsequent values of Io. Perturbations for 10 min or more produced a "memory" effect both with and without aldosterone: accelerating sodium transport by negative clamping lowered the subsequent value of Io; positive clamping induced the opposite effect. Changes in Jro were more readily detectable in the presence of aldosterone; these were in the same direction as the changes in Io. The linearity of Jr in Δψ indicates the validity of analysis in terms of linear nonequilibrium thermodynamics—brief perturbations of Δψ appear to produce no significant effect on either the phenomenological coefficients or the free energy of the metabolic driving reaction. Hence it is possible to evaluate this free energy.

Effects of biguanides on short-circuit current in frog skin

1984 ◽  
Vol 247 (2) ◽  
pp. F277-F281
Author(s):  
T. Saito ◽  
S. Yoshida
Keyword(s):  
Sodium Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Apical Surface ◽  
Sodium Permeability ◽  
Total Conductance ◽  
Mucosal Side ◽  
Stimulation Of

The addition of phenformin to the solution bathing the mucosal side of frog skin resulted in a sustained stimulation of short-circuit current accompanied by an increase in open-circuit potential and total conductance of the membrane. The flux of 22Na from the mucosal to the serosal side of the skin was increased by phenformin, whereas no significant effect on the flux from the serosal to the mucosal side was observed. The increases in the short-circuit current and total conductance with phenformin were completely abolished by the addition of 5 X 10(-5) M amiloride, which blocks sodium permeability at the apical surface of the membrane. Thus, the stimulation of active sodium transport in frog skin by phenformin would be due to the increase in the amiloride-sensitive sodium permeability of the membrane. Phenformin may prove to be a useful tool for the study of sodium transport in amphibian epithelia.

Effect of acetylcholine on Cl- and Na+ fluxes across dog tracheal epithelium in vitro

1976 ◽  
Vol 231 (5) ◽  
pp. 1546-1549 ◽  
Author(s):  
MG Marin ◽  
B Davis ◽  
JA Nadel
Keyword(s):  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Atropine Sulfate ◽  
Open Circuit ◽  
Ion Flux ◽  
Potential Difference ◽  
Tracheal Epithelium ◽  
Electrical Potential Difference

Electrical potential difference is generated across canine tracheal epithelium by active transport of Cl- toward and Na+ away from the lumen. The present study examines the effects of acetylcholine on short-circuit current, potential difference, resistance, and fluxes of 36Cl and 24Na measured across pieces of canine tracheal epithelium mounted in Ussing-type chambers. Under short-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly net ion flux toward the lumen of Cl- (n equals 7) from +1.7 +/- SE 0.5 TO +3.3 +/- SE 0.5 mueq/cm2 - h, and of Na+ (n equals 7) from -0.8 +/- SE 0.2 to +0.5 +/- SE 0.2 mueq/cm2 - h. Under open-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly the unidirectional flux of Cl- (n equals 6) toward the lumen from 4.7 +/- SE 1.3 to 5.9 +/- SE 1.4 mueq/cm2 - h, while the other measured fluxes did not change significantly, suggesting that net Cl- flux had increased toward the lumen. Atropine sulfate (10(-8) M) prevented the response to acetylcholine (5 X 10(-5) M). The increased ion flux due to acetylcholine may mediate water secretion into the airway lumen, and this secretion may have important effects on the physical properties of the liquid through which the respiratory cilia beat.

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