Effects of Aminoperimidine on Electrolyte Transport across Amphibian Skin

Abstract

The effect of aminoperimidine (AP) on transepithelial Na⁺ transport and Cl^– conductance (G^Cl) of isolated amphibian skin (Bufo viridis and Rana esculenta) was analyzed using transepithelial and intracellular electrophysiological techniques. AP, applied at concentrations between 30 and 100 µM from the mucosal side, stimulated Na⁺ transport rapidly and reversibly by more than 30% of the control value due to an increase in apical membrane Na⁺ permeability. Influence of AP on basolateral membrane conductance and effective driving force for Na⁺ were negligible. Voltage-activated G^Cl of toad skin, but not the resting, deactivated conductance, as well as spontaneously high G^Cl in frog skin was rapidly inhibited by AP in a concentration-dependent manner. The half-maximal inhibitory concentration of 20 µM is the highest hithero reported inhibitory power for G^Cl in amphibian skin. The effect of AP on G^Cl was slowly and incompletely reversible even after brief exposure to the agent. Serosal application of AP had similar, albeit delayed effects on both Na⁺ and Cl^– transport. AP did not interfere with the Cl^– pathway after it was opened by 100–300 µM CPT-cAMP, a membrane-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage-activated G^Cl by AP was attenuated or missing when AP was applied during voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl^– pathway at a certain distance from the external surface. AP affects then the Na⁺ and Cl^– transport pathways independent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na⁺ and Cl^–, remains to be elucidated.

Selective inhibition of Cl− conductance in toad skin by blockers of Cl− channels and transporters

“…Under these conditions, G Cl is only marginally influenced by the inhibitors of cotransporters or antiporters but readily inhibited by the channel blockers, albeit at a notably lower affinity. Similar decrease in the sensitivity of the cAMP-induced G Cl has been observed previously with other inhibitors of the Cl Ϫ pathway such as aminoperimidine (27), N-ethylmaleimide (23), and CN Ϫ (26), which hints at the possibility that high concentrations of cAMP alter the internal structure of the Cl Ϫ pathway. Under these conditions, the sensitivity of toad skin G Cl to the derivatives of DPC is shifted toward the range observed for CFTR (20,34), although the cAMP-induced G Cl of toad skin is still notably more sensitive.…”

“…Erythrosine and the DPC derivatives (DCDPC, FFA, and NA) are among the most powerful inhibitors of the voltage-activated G Cl in toad skin. Comparable inhibitory potency has hitherto only been reported for aminoperimidine (27) and cyanide (26). Less powerful compounds are eosin, furosemide, DPC, and NPPB, which nevertheless are still more effective than another previously reported inhibitor, .…”

Transepithelial chloride conductance in amphibian skin: regulatory mechanisms and localization

“…Highaffinity interference of the ionic CN -with selective sites in the pathway proper was suggested as a mode of action [59]. N-Ethyl maleimide inhibits the voltage-activation step more effectively, as does aminoperimidine [60]; these agents might primarily, but not exclusively, act on the voltage sensor or the associated signal cascade. Since serosal trypsin decreases the voltage-activated G Cl reversibly, but does not affect the cAMP-induced conductance [56], interference with as yet unidentified steps within the signal transduction process appears feasible.…”