Inhibitory and stimulatory effects of amiloride analogues on sodium transport in frog skin

Li, J. H.; Sousa, R. C. de

doi:10.1007/bf01961378

Cited by 27 publications

(8 citation statements)

References 23 publications

(23 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The rapid inhibition observed with amiloride is consistent with an effect on the luminal membrane; no inhibition was observed when excess amiloride (up to 1 mM) was added to the serosal side ofany ofthe tissues (results not shown) (7). The mechanism of amiloride action as a specific inhibitor of sodium current has been well established in various species (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)27). The effect of amiloride in the present studies was similar to that in studies in which the specificity for sodium transport has been rigorously established (3,4,(6)(7)(8).…”

Section: Resultsmentioning

confidence: 53%

Inhibition of amiloride-sensitive sodium conductance by indoleamines.

Legris¹,

Will²,

Hopfer³

1982

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

To examine a possible role of indoleamines in the regulation of epithelial sodium absorption, the effect of serotonin (5-hydroxytryptamine) and several derivatives on electrolyte transport was measured in vitro in the baboon bronchus and in the trachea and colon of sodium-deficient rats. Serotonin,, and harmaline (1-methyl-7-methoxy-3,4-dihydro-P-carboline) inhibited sodium transport in all three preparations in a similar manner to the natriuretic agent amiloride. In all three epithelia, sodium absorption via the amiloride-sensitive pathway constitutes a substantial portion of total electrolyte transport, measured as the amiloride-sensitive shortcircuit current. Thus, 25 FM amiloride inhibited the short-circuit current 21% in the rat trachea, 63% in the baboon bronchus, and 90% in the rat colon. Serotonin, melatonin, and harmaline inhibited the amiloride-sensitive portion of the short-circuit current from the luminal side of the epithelium. The inhibition was rapid, requiring only seconds, and maximal inhibition by serotonin was identical to that by amiloride. When sodium was omitted from the luminal solution, the short-circuit current was reduced a similar amount, suggesting that sodium absorption was being inhibited by both amiloride and the indoles. The IC50 value for amiloride was 50 nM in the baboon bronchus and 500 nM in the rat colon. In contrast, the IC50 value for serotonin was 0.4 mM in the baboon bronchus and 8 mM in the rat colon. These results, together with the wide distribution of amine-precursor-uptake-and-decarboxylation (APUD) cells in the respiratory and intestinal tract, suggest that certain indoleamines could play a role as local regulators of fluid and electrolyte transport. For example, in the airways, indoleamines may be one of the factors involved in regulation of the depth of the periciliary fluid layer.Amiloride is a potassium-sparing diuretic that, at micromolar concentrations, inhibits sodium absorption in many epithelia that scavenge sodium from the luminal or external side of the epithelium (1, 2). Amiloride inhibits sodium absorption by blocking a specific sodium channel or pore in the luminal plasma membrane of epithelial cells so that sodium cannot enter the cell from the luminal side (2-13). Because of its specificity, amiloride has been used to operationally define a certain type of sodium transport that can be quantitated as the amiloridesensitive short-circuit current in vitro in epithelial preparations.Epithelial sodium transport plays a crucial role in maintaining electrolyte balance in higher animals. The importance of this transport suggests that efficient regulatory mechanisms have evolved. However, no physiological compounds are known that can rapidly inhibit sodium absorption through the amiloridesensitive pathway-i. e., one that acts similar to the drug. The currently known regulatory mechanism is through adrenal steroids that induce amiloride-sensitive sodium transport (1, 5).Regulation by adrenal steroids is on the time scale of hours (1, 14, 15), rather t...

show abstract

Section: Resultsmentioning

confidence: 53%

Inhibition of amiloride-sensitive sodium conductance by indoleamines.

Legris¹,

Will²,

Hopfer³

1982

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…The substitution of both hydrogen atoms on the 5-amino nitrogen by methyl groups yields a compound of net stimulatory activity in the concentration range from 1/*M to 1 mM (Li & DeSousa, 1979;Li & Lindemann, 1983a). The spectra taken in the presence of this analog (AA8) alone did not show a clear Lorentzian component in the frequency range of 0.1 to 100 Hz.…”

Section: Halo-substitution At Ring Position-6mentioning

confidence: 90%

Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: I. Pyrazine-ring modifications

Cragoe

Lindemann

1985

J. Membrain Biol.

View full text Add to dashboard Cite

The overall on- and off-rate constants for blocking epithelial Na channels by amiloride analogs were estimated by noise analysis of frog skin epithelium. The substituents at position-5 and -6 of the pyrazine ring of amiloride were varied in order to obtain the structure/rate constant relationship. (1) The off-rate constant increases with halo-substitutions at position-6 in the order Cl less than Br less than l less than F less than H. Substitution of Cl by H lowers the standard free energy of activation of the off-step by 2.3 kcal mol-1. The on-rate constant is not affected. Apparently the substituent at ring position-6 controls the duration of attachment in the blocking position. pKa considerations show that the duration is longer when the 6-substituent is more negatively polarized. We suggest that this substituent binds to the receptor by virtue of its electronegativity. (2) In contrast, replacement of the adjacent 5-amino group (electron donor) by H or Cl affects both the on-rate and the off-rate. The dual effect may be explained by a decrease of the electronic charge at more remote parts of the molecule (on-rate decrease), as well as at the 6-position (off-rate increase). Apparently the 5-amino group stabilizes the blocking position by increasing the electron density on the 6-ligand.

show abstract

“…Recently Thurman and Higgins (1982) showed that in the toad urinary bladder amiloride develops a strong stimulatory effect on Na uptake when applied in low concentrations in the presence of Ca ions and a divalent cation chelator. The amiloride analog benzamil was also seen to have an additional stimulating effect, at least with spironolactone-pretreated frogs (Cuthbert & Shum, 1976), while the 5-dimethyl analog is even predominantly stimulatory in frog skin (Li and DeSousa, 1979). Benzimidazolyl guanidine (BIG) was found to stimulate strongly up to concentrations of 1 m~ (Zeiske & Lindemann, 1974).…”

Section: Introductionmentioning

confidence: 99%

Chemical stimulation of Na transport through amiloride-blockable channels of frog skin epithelium

Lindemann

1983

J. Membrain Biol.

View full text Add to dashboard Cite

The stimulation of apical Na permeability caused by a number of reagents effective from the outer side of the membrane was investigated by fluctuation analysis. In the epidermis of R. ridibunda, parachloromercuriphenyl sulfonate (PCMPS) and benzimidazolyl guanidine (BIG) increase the number (N0) of conducting Na channels by releasing channels from Na self-inhibition. As a consequence, the apparent macroscopic affinity for amiloride is increased. 5-dimethyl amiloride and trinitrobenzene sulfonate (TNBS) also cause reversible stimulation by increasing N0; here release from self-inhibition is less clear. With each of the four stimulators investigated, the Na channel current remained unaffected or was only marginally increased. In addition to its stimulatory effect, TNBS caused irreversible blockage of Na channels. Apart from their stimulatory effects, BIG and 5-dimethyl amiloride, both of which have a side-chain terminated with an amidino group, are high rate-blocking competitors of amiloride.

show abstract

Inhibitory and stimulatory effects of amiloride analogues on sodium transport in frog skin

Cited by 27 publications

References 23 publications

Inhibition of amiloride-sensitive sodium conductance by indoleamines.

Inhibition of amiloride-sensitive sodium conductance by indoleamines.

Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: I. Pyrazine-ring modifications

Chemical stimulation of Na transport through amiloride-blockable channels of frog skin epithelium

Contact Info

Product

Resources

About