Effects of amiloride analogues on human erythroleukemic K562 cell growth and on induction of hemoglobin synthesis by adriamycin.

Treatment with adriamycin for 8-14 h irreversibly induces K562 human erythroleukemic cells to synthesize hemoglobin. With 16-h exposure, this effect is maximal at concentrations between 180 and 400 nM, yielding 70%-90% benzidine-positive (B+) cells and 24 pg/cell hemoglobin 4 days after the beginning of adriamycin treatment. This induction is accompanied by changes in ouabain-sensitive 86Rb influx opposite to those seen with murine erythroleukemic (MEL) cells. Amiloride and several amiloride analogues strongly inhibit adriamycin induction of hemoglobin synthesis as well as cell growth in the absence of adriamycin. The inhibition of induction is enhanced with the analogues bearing a benzyl or substituted benzyl group on the 5-amino or on a terminal guanidino nitrogen atom. The effect on growth was somewhat greater with the analogue bearing a 2-chlorobenzyl moiety on a terminal guanidino nitrogen atom and with the one bearing a 2-fluorobenzyl group on the 5-amino nitrogen atom. The structural features required for growth inhibition resemble those seen with MEL cells, but the features required for inhibition of induction of hemoglobin synthesis are completely different. These data suggest that different specific binding sites are involved in these two effects of amiloride and its analogues.

An isoelectric focusing procedure for erythrocyte membrane proteins and its use for two-dimensional electrophoresis.

Procedures are described and evaluated for one-dimensional isoelectric focusing of erythrocyte membrane dissolved in lysine, urea, and Triton X-100 without using sodium dodecyl sulfate (SDS) and for two-dimensional electrophoresis with SDS in the second dimension. The membrane was completely dissolved, most of the proteins including the anion porter(s) entered the focusing gel, and complex, well-resolved patterns were seen. Ampholines, 2-mercaptoethanol, or SDS in the applied sample each seriously reduced focusing resolution and phenylmethylsulfonyl fluoride blurred the patterns. The two-dimensional patterns showed more and sharper spots than did patterns obtained from membrane initially dissolved with SDS. Anion porter spots were seen with both procedures. However, major cytoskeletal proteins were much less well recovered with the former procedure than with the latter.

Anion transport heterogeneity detected by flow cytometric measurement of NBD-taurine efflux kinetics.

NBD-taurine [N-(7-nitrobenzofuran-4-yl) taurine], a fluorescent substrate for the human erythrocyte anion exchange system, has been used to test the feasibility of making flow cytometric measurements of anion transport in K562 erythroleukemic cells. Cells were preloaded by incubation with 20 microM-2mM NBD-taurine, then diluted 10-30-fold, and efflux was monitored by measuring fluorescence intensity (FL) as a function of time using excitation at 488 nm. The observed rate of decrease in fluorescence was sensitive to temperature and also to phloretin, a compound known to inhibit anion transport and other carrier-mediated transport processes. The coefficient of variation (CV) of the fluorescence distribution increased markedly over the efflux period, suggesting heterogeneity of the K562 population with respect to the rate constant for NBD-taurine efflux. This heterogeneity was also reflected in the upward curvature of a first order plot of log (FLt - FL infinity) versus time. Half-times calculated from initial linear portions of the first-order plots were found to decrease as the loading concentration of NBD-taurine was decreased, as predicted for a saturable transport system. NBD-taurine is not an ideal anion transport substrate for flow cytometric studies. It appears to bind to high-affinity sites within the cells with consequent fluorescence quenching, complicating interpretation of kinetic curves at low concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)