Effect of external cation and anion substitutions on sodium transport in isolated frog skin

Abstract

Effects of changes in external ionic strength, external cation and/or anion substitution on transepithelial influx and efflux of sodium, short-circuit current and on transepithelial potential difference and resistance were studied in isolated frog skin. Active transport of Na was found to be highly dependent on both anionic and cationic composition of external medium. Relative abilities of external monovalent cations to inhibit active Na transport were H greater than Li greater than K greater than Rb greater than Cs greater than choline. Relative abilities of external monovalent anions to stimulate active Na transport were I greater than Br greater than Cl. Sequences of anion interaction and of resistance changes suggest that anionic stimulation of Na transport is not due to electrical coupling across outer cell membrane. The ability of different anions and cations to alter Na transport suggests that externally located charged groups act as important barriers or filters to ion movement. In addition, the experiments suggest that an increase in ionic strength of external medium has an effect on active transport of Na, a finding that indicates interference of surface charges with Na entry. Directional changes in efflux of Na due to changes in ionic composition of external medium usually paralleled changes in active Na transport. It is possible that the observed relationship between influx and efflux of Na is the result of common pathways and of interaction of the active transport system with Na efflux.

Dependence of water movement on sodium transport in kidney proximal tubule: A microperfusion study substituting lithium for sodium

“…1) The permeability of the luminal membrane, and therefore Na entry into the cell, is a function of the external Na concentration [32,2], or…”

Effect of FeCl3 on ion transport in isolated frog skin

“…In a detailed study, Biber and Mullen [6] showed that Na transport is inhibited by monovalent alkali cations and that the order of inhibition increases with decreasing ion crystal radii in accordance with Eisenman's sequences X or XI. This observation suggests the presence of a strong anionic electric field sufficient to overcome the hydration forces of the alkali cations.…”

“…Hence, the inhibitory action on Na transport might arise from the binding of Fe 3 § to negatively charged groups associated with a carrier or a charged ion channel site in the outer cell membranes and/or from modifications in general surface charge. Studies by Biber and Mullen [6], Singer and Civan [28]~ and Zeiske and Lindemann [31] have indicated that charged sites may serve as filters or binding sites for the translocation of Na across the external surface of the frog skin.…”

“….... across the external surface of frog skin [1,6,28,31]. To further analyze the importance of charge interaction on active transport processes, we studied the effects of external Fe 3 § an ion which is very electropositive because of its high charge and small radius, on Na transport in the isolated skin of Rana pipiens.…”

Acid–base and electrolyte responses to low pH maintained by phosphate–citrate buffers in the bathing medium of the larval salamander Ambystoma tigrinum

“…Mannitol is commonly used to maintain total solute constant in studies of amphibian skin ion fluxes and has no apparent adverse affects (Biber and Mullen 1980).…”