HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Cavieres, J. D. Articles by Ellory, J. C. Search for Related Content PubMed PubMed Citation Articles by Cavieres, J. D. Articles by Ellory, J. C.

1. Thallium (Tl) inhibits the ouabain-sensitive K influx in human red cells in high-Na medium. At 1 mM external K concentration [K_o], the ouabain-sensitive K influx decreases steadily with increasing Tl concentration, up to 0·9 mM outside; at 0·17 mM-K_o, however, Tl stimulates the ouabain-sensitive K influx below 0·1 mM-Tl_o and inhibits it at higher concentrations.

2. In a K-free medium in which all except 5 mM-Na is replaced by choline, and into which red cells show zero control ouabain-sensitive Na efflux, Tl is able to support ouabain-sensitive Na efflux up to 2·1 m-mole/l. cells.hr following a sigmoid activation curve which is half-maximal between 0·03 and 0·05 mM-Tl_o and that follows two-site kinetics up to 0·1 mM-Tl_o. Beyond 0·15 mM-Tl_o, the Tl-activated ouabain-sensitive Na efflux attained is inhibited slightly.

3. When the ouabain-sensitive Na efflux is measured at 5 mM-Na_o and 5 mM-K_o, increasing concentrations of Tl have little effect on it, 0·9 mM-Tl_o inhibiting by some 14%; in similar conditions, the ouabain-sensitive K influx is inhibited by about 40%.

4. The dependence of ouabain-sensitive K influx on external K concentration at 5 mM-Na_o, which follows a slightly sigmoid curve in the absence of Tl, changes to hyperbolic at 0·06 mM-Tl_o at the same time that ouabain-sensitive K influx is inhibited. The fitted V_max values for ouabain-sensitive K influx are the same in the presence and in the absence of 0·06 mM-Tl_o.

5. In high-Na cells, loaded by nystatin treatment, the ouabain-sensitive K influx measured at 0·2 mM-Na_o follows a hyperbolic curve between 0·05 and 0·4 mM-K_o, and is inhibited by Tl in a strictly competitive fashion.

6. The effects of Tl on ouabain-sensitive Na efflux and ouabain-sensitive K influx are interpreted in terms of a high-affinity substitution for K at the external K sites of the Na pump and suggest that in human red cells Tl can be actively transported inwards in exchange for internal Na.

7. Thallium can inhibit about 25% of the ouabain-insensitive Na efflux into 5 mM-Na_o and part of this inhibition occurs with a high Tl-affinity; the ouabain-insensitive K influx is inhibited by Tl both in high-Na and in 5 mM-Na medium, but with a different concentration dependence than the ouabain-insensitive Na efflux.