Kinetics of Na-Li exchange in high and low K sheep red blood cells

Abstract

The kinetic parameters and transport mechanism of Na-Li exchange were studied in both low K (LK) and high K (HK) sheep red blood cells with cellular Na [( Na]i) and Li concentrations [( Li]i) adjusted by the nystatin technique (Nature New Biol. 244: 47-49, 1973 and J. Physiol. Lond. 283: 177-196, 1978). Maximum velocities (Vm) for Li fluxes and half-activation constants (K1/2) for Li and Na of the Na-Li exchanger were determined. The K1/2 values for both Li and Na appeared to be similar in both cell types, although they were about two to three times lower on the inside than on the outside of the membrane. Furthermore, the K1/2 values for Li were at least an order of magnitude smaller than those for Na, suggesting substantial affinity differences for these two cations. The Vm values for Li fluxes, on the other hand, appear to be lower in HK than in LK cells. When Na and Li fluxes were measured simultaneously, a trans stimulatory effect by Na on Li fluxes was observed. From measurements of Li influx at different concentrations of external Li and different [Na]i, the ratio of the apparent Vm to the apparent external Li affinity was calculated to be independent of [Na]i for both types of sheep red blood cells. Similar trans effects of external Na were observed on Li efflux at varying [Li]i. These results are expected for a system operating by a "ping-pong" mechanism.

Effect of cholesterol and dipalmitoyl phosphatidylcholine enrichment on the kinetics of Na−Li exchange of human erythrocytes

“…In a control experiment it was found that an increase of intraceilular Na from 6.95 to 38.7 mmol/ liter accelerated Vm~ x ofphloretin-sensitve Li uptake by about 2.5-fold (from 0.20 to 0.51 mmol (liter cells 9 hi') ~). In addition, the apparent KNLi,, was considerably higher in Na-loaded cells (3.85 in Na-loaded vs. 1.35 mmol/liter in untreated erythrocytes), in accordance with results previously reported for human and sheep erythrocytes [17,24]. In Na-loaded red cells (Fig.…”

Signal transduction mechanisms of K+‐Cl− cotransport regulation and relationship to disease

“…Li + also modulates the transport of other cations (i.e. Ca 2+ , K + and H + ) through competition or allosteric mechanisms (Somolo & Hasson‐Voloch 1987, Ryu et al. 1989, Davis et al.…”

Lithium Fluxes Indicate Presence of Na-Cl Cotransport (NCC) in Human Lens Epithelial Cells

“…Thereafter, cells were exposed, usually for a period of 5-15 min to the following flux media: For Rb influx, the K congener 85 Rb has been shown in many of our previous publications to accurately substitute for K in these uptake measurements, and the media were BSS-Rb/XCl-BSA or BSS-Rb/XSf-BSA where X stands for either Na or Li used at varying concentrations as described in Results. For Li influx, the non-isotopic ion was used as in previous studies in erythrocytes [14,18,19] and the flux solutions were BSS-LiYCl-BSA or BSS-LiYSf/NO 3 -BSA where Y stands for K or NMDG used at concentrations mentioned in Results. Details deviating from these procedures are addressed in the description of the experiments and also noted in the Figure Legends.…”

“…Ions were extracted with 5% perchloric acid and protein was determined after solubilization in 1 N NaOH using the bicinchonic acid (BCA) method. Li was measured by atomic absorption at 670.8 nm and Rb by flame emission at 780 nm using a Perkin Elmer 5000 atomic absorption spectrophotometer [18]. Rb or Li uptake are expressed in nmoles/mg protein, and the fluxes in nmoles/mg protein per 5 and 15 min, respectively.…”