Trapping of 134Cs+ in frog skin epithelium as a function of short circuit current

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.

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Effects of choline and other quaternary ammonium compounds on Na movements in frog skin

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1963.205.5.1063 ◽

1963 ◽

Vol 205 (5) ◽

pp. 1063-1066 ◽

Cited By ~ 12

Author(s):

Robert I. Macey ◽

Daniel C. Koblick

Keyword(s):

Quaternary Ammonium ◽

Frog Skin ◽

Short Circuit ◽

Short Circuit Current ◽

Quaternary Ammonium Compounds ◽

Average Increase ◽

Current Increase ◽

Sodium Flux ◽

Radioactive Sodium ◽

Ammonium Compounds

Effects of choline on short-circuit current and radioactive sodium flux were measured in isolated frog skins. Replacement of control ions (K or Mg) by choline in the outside solution increased the short-circuit current and inward Na flux. When K was the control ion, the average increase in short-circuit current was 52%; with Mg, it was 36%. In both cases, the increase in inward Na flux accounted for about 75% of the short-circuit current increase, while passive choline movement possibly accounted for the remainder. Similar results were obtained using tetramethylammonium and tetraethylammonium in place of choline. One implication of these results is that studies in which choline is used as an inert substitute for Na must be interpreted with caution.

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Potassium uptake across serosal surface of isolated frog skin epithelium

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1972.222.6.1366 ◽

1972 ◽

Vol 222 (6) ◽

pp. 1366-1373 ◽

Cited By ~ 33

Author(s):

TU Biber ◽

J Aceves ◽

LJ Mandel

Keyword(s):

Frog Skin ◽

Potassium Uptake ◽

Skin Epithelium ◽

Frog Skin Epithelium ◽

Serosal Surface

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Effect of amiloride and some of its analogues of cation transport in isolated frog skin and thin lipid membranes.

The Journal of General Physiology ◽

10.1085/jgp.68.1.43 ◽

1976 ◽

Vol 68 (1) ◽

pp. 43-63 ◽

Cited By ~ 70

Author(s):

D J Benos ◽

S A Simon ◽

L J Mandel ◽

P M Cala

Keyword(s):

Lipid Membranes ◽

Frog Skin ◽

Short Circuit ◽

Short Circuit Current ◽

Active Species ◽

Biologically Active ◽

Lipid Bilayer Membranes ◽

Inhibitory Interaction ◽

Charged Form ◽

Transport Site

The inhibition of short-circuit current (Isc) in isolated frog skin and the induction of surface potentials in lipid bilayer membranes produced by the diuretic drug amiloride and a number of its chemical analogues was studied. The major conclusions of our study are: (a) The charged form of amiloride is the biologically active species. (b) Both the magnitude of Isc and the amiloride inhibitory effect are sensitive to the ionic milieu bathing the isolated skin, and these two features are modulated at separate and distinct regions on the transport site. (c) Amiloride is very specific in its inhibitory interaction with the Na+ transport site since slight structural modifications can result in significant changes in drug effectiveness. We found that substitutions at pyrazine ring position 5 greatly diminish drug activity, while changes at position 6 are less drastic. Alterations in the guanidinium moiety only diminish activity if the result is a change in the spatial orientation of the amino group carrying the positive charge. (d) Amiloride can bind to and alter the charge on membrane surfaces, but this action cannot explain its highly specific effects in biological systems.

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Cl transport across the basolateral membrane in frog skin epithelium

Pflügers Archiv - European Journal of Physiology ◽

10.1007/bf00581772 ◽

1985 ◽

Vol 405 (S1) ◽

pp. S8-S11 ◽

Cited By ~ 18

Author(s):

Adolf D�rge ◽

Roger Rick ◽

Franz Beck ◽

Klaus Thurau

Keyword(s):

Frog Skin ◽

Basolateral Membrane ◽

Skin Epithelium ◽

Cl Transport ◽

Frog Skin Epithelium

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Calcium channel blockers inhibit amiloride-stimulated short-circuit current in frog tadpole skin

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1992.263.4.r827 ◽

1992 ◽

Vol 263 (4) ◽

pp. R827-R833 ◽

Cited By ~ 1

Author(s):

T. C. Cox

Keyword(s):

Calcium Channel ◽

Calcium Channel Blockers ◽

Time Course ◽

Frog Skin ◽

Short Circuit ◽

Short Circuit Current ◽

Cation Channels ◽

Channel Blockers ◽

Ussing Chambers ◽

Frog Tadpole

The larval frog skin has a very high electrical resistance and a corresponding low rate of transepithelial ion transport. Amiloride, a blocker of sodium transport in adult skin, transiently stimulates rather than inhibits short-circuit current (Isc) across larval skin. The time course and concentration response to amiloride and the effects of calcium channel blockers on Isc were studied with larval frog skin mounted in modified Ussing chambers. The amiloride (1 mM) transient was markedly blunted if the skin was previously exposed to low amiloride (0.01-0.1 mM) concentrations. The calcium channel blockers verapamil, nitrendipine, diltiazem, W-7, and lanthanum all blocked the amiloride transient. Diltiazem itself caused a rapid transient in Isc, indicating that it may be a partial agonist. These data suggest that the amiloride-stimulated cation channels rapidly desensitize in a manner similar to the acetylcholine receptor. The decline in Isc after amiloride stimulation could be caused by amiloride block of the open channel. Blockade of amiloride stimulation by well-known calcium channel blockers suggests that these larval cation channels may have some characteristics in common with calcium channels.

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