Effects of Metabolic Inhibitors and Drugs on Ion Transport and Oxygen Consumption in Isolated Frog Skin

Abstract

Active ion (NaCl) transport across isolated frog skin is discussed in relation to sodium and potassium composition and to O3 consumption of skin. A distinction is made between processes in skin related to "unidirectional active ion transport" and processes related to "maintenance electrolyte equilibrium;" i.e., ionic composition of skin. Several metabolic inhibitors were found that could be used in separating maintenance electrolyte equilibrium from unidirectional active ion transport. Fluoroacetate (up to 1 X 10-M/liter) did not affect maintenance electrolyte equilibrium, but severely diminished the rate of active ion transport. This could also be accomplished with azide and diethyl malonate when 1 X 10 -3 molar concentrations were used. When applied in higher concentrations, these two inhibitors, and several others, diminished active ion transport, but this was associated with changes in maintenance electrolyte equilibrium (gain of Na + by and loss of K + from skin). Similar observations were made when skins were subjected to K+-deficient media. Mersalyl and theophylline, in low concentrations, stimulated active ion transport without leading to changes in maintenance electrolyte equilibrium. Inhibition of'active ion transport was found accompanied by decrease, increase, and unaltered over-all 03 consumption, depending on the kind of chemical agent used. A provisional scheme of the mechanism of unidirectional active ion transport is proposed. It is conceived as a process of metabolically supported ion exchange adsorption, involving a carrier, forming complexes with K + and Na +, a trigger, K + ions, and two spatially separated metabolic pathways.

Ionic fluxes in isolated epithelial cells of the abdominal skin of the frogLeptodactylus ocellatus

“…Iodoacetate 10-4M produces an inhibition of 17 ~o. This agrees with the evidence that both the glucolytic pathway and the Krebs cycle are in operation in the epithelium of the frog skin (Huf, Doss & Wills, 1957;Skjelkvale, Nieder & Huf, 1960;Curran & Cereijido, 1965). It also agrees with the observation that the inhibition of a single metabolic pathway does not supress completely the transepithelial transport of Na (Leaf & Renshaw, 1957).…”

“…9 shows that the removal of Ca 2 + plus the addition of 2 mM EDTA (third column) produce a small increase (22-23 %) of the rate constant for Na extrusion. This might be attributed to an increased leakiness of the cells, as Huf et al (1957) have shown that skins incubated with EDTA lose K and gain Na. In the present case though, the cells have been exposed to EDTA for a period starting only 3 min before the measurements of unidirectional fluxes are made, and this time is too short to detect changes in the composition of the cell.…”

The effect of sodium concentration on the content and distribution of sodium in the frog skin

“…This agrees with the results showing that the sodium involved in the mechanism of transport across the skin is contained in a compartment separated from the rest of the epithelial sodium. It is conceivable that the possibility of stopping the net transport across the epithelium without disturbing the electrolyte balance, using either metabolic inhibitors (Huf, Doss & Wills, 1957) or xantines (Levinsky & Sawyer, 1953), arises from the separation of the Na involved in these functions observed in the present study. The studies of , demonstrating that the balance of potassium is independent of the concentration of sodium in the outer bathing solution and ofthe magnitude of the net transport of sodium, give further support to the viewthat the Na undergoing net transfer does not get directly involved in the ionic equilibration of the cell.…”

Computer simulation of sodium fluxes in frog skin epidermis

“…The experimental data on skin epidermis referred to above, therefore, may be considered as a strong argument in favor of involvement of several compartments within the epidermis, as is also evidenced by its fine structure. Earlier work from this laboratory [22,40] had led us to conclude that there must be compartmentalized functions in the handling of Na + and K + metabolism in skin epidermis: one concerned with "maintenance electrolyte equilibrium", another with "unidirectional active ion transport". The analysis of the electrical response of the outer border of skin to changes in [Na+]o supports this view [30].…”

“…The model results (10B vs. 10E and 11 D) are in agreement with these findings. Zerahn [43] found that ouabain which is often said to specifically inhibit the Na + pump, as does fluroacetate [22] decreases J, and greatly increases the total Na + pool. This has been confirmed by Nagel and D6rge [26], and by Aceves and Erlij [1] except that these authors do not find the pool changed because of more Na + entering from the outside.…”