Kinetic characteristics of the sulfate self-exchange in human red blood cells and red blood cell ghosts

Abstract

Summary. The sulfate and the chloride self-exchange fluxes were determined by measuring the rate of the tracer effiux from radioactively labeled human red blood cells and red blood cell ghosts. The concentration dependence and the pH-dependence of the sulfate self-exchange flux were studied. In addition, the effects of some monovalent and divalent anions on the sulfate and the chloride self-exchange fluxes were investigated.The sulfate self-exchange fluxes saturate, exhibiting a concentration maximum at sulfate concentrations between I00 and 300 mM (25 ~ The position of the concentration maximum depends upon pH. At high sulfate concentrations a self-inhibition of the flux becomes apparent. The apparent haft-saturation constant and the apparent self-inhibition constant at pH 7.2 were 30 mM and 400 mM respectively. Within the pH range of 6.3-8.5, both constants decreased with increasing pH. No saturation of the sulfate self-exchange flux was observed if the sulfate concentration was raised by substituting sulfate for isoosmotic amounts of a second salt (NaC1, NaNO3, Na-acetate, Na-lactate, Na-succinate or Na2HPO4). Red blood cells and red blood cell ghosts display the same pattern of concentration responsiveness.The sulfate self-exchange flux exhibits a pH-maximum at about pH 6.2 (37 ~ The location of the pH-maximum is little affected by variations of the sulfate concentration. The logarithmic plots (log Jso4 vs. pH) revealed that the flux/pH relation can be approximated by two straight lines. The slopes of the alkaline branches of the flux/pH curves range from -0.55 to -0.86, the slopes of the acidic branches of the curves range from 0.08 to 1.14 and were strongly affected by changes of the sulfate concentrations. The apparent pK's obtained from the alkaline and from the acidic branches of the flux/pH curves were about 7.0 and 6.0, respectively. Intact red blood cells and red blood cell ghosts display the same type of pH-dependency of the sulfate self-exchange flux.The sulfate self-exchange flux is competitively inhibited by nitrate, chloride, acetate, oxalate and phosphate. The chloride self-exchange flux is competitively inhibited by thiocyahate, nitrate, sulfate and phosphate. The inhibition constants for the various anion species increase in the given sequence.The results of our studies indicate that the sulfate self-exchange flux is mediated by a "two-site transport mechanism" consisting either of a mobile carrier or a two-site pore. The experiments reported in this paper do not permit distinguishing between both transport mechanisms. The similarities of the sulfate and the chloride self-exchange flux and the mutual competition between sulfate and chloride point to a common transport system for both anion species.

The influence of lipid composition on the barrier properties of band 3-containing lipid vesicles

“…Chemicals and radiochemicals used were from the following sources: Na35SO4 (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) (10.7 Ci/nmol) from New England Nuclear. Stractan (arabino galactan) from Sigma.…”

Oxidation as a possible mechanism of cellular aging: vitamin E deficiency causes premature aging and IgG binding to erythrocytes.

“…The "self-exchange flux" of sulfate was determined from the sulfate exchange at Donnan equilibrium, essentially following the method of Lepke and Passow (57) and Schnell et al (58). Erythrocytes were assayed either the same day or 1 day after the blood was collected.…”

“…"Influx" experiments were performed according to Schnell et al (58) with the following modifications (P. Hallaway and J. W. Eaton, personal communication). Washed cells were suspended at 3-4 x 108 cells per ml in Hanks' balanced salt solution, containing various concentrations of sulfate (pH 7.4) and equilibrated at 37°C for 1 hr.…”

Erythrocyte Aging Characteristics in Elderly Individuals With Beginning Dementia

“…The Km and VmaK values of sulfate exchange, however, did not differ significantly between old and young donors. As sulfate transport is 10,000 times slower than that of the physiological-chloride/bicarbonate ex change (18), these parameters may not be sensitive enough to detect small changes. Together, these data indicate that in old individuals the rate of the erythrocyte aging process is increased.…”