R. Deves et S. Angelo, CHANGES IN MEMBRANE AND SURFACE-POTENTIAL EXPLAIN THE OPPOSITE EFFECTS OF LOW IONIC-STRENGTH ON THE 2 LYSINE TRANSPORTERS OF HUMAN ERYTHROCYTES, The Journal of biological chemistry, 271(50), 1996, pp. 32034-32039
The sucrose-induced stimulation of lysine influx in human erythrocytes
has been attributed to the removal of a competitive inhibition exerte
d by Na+ on system y(+) (Young, J. D., Fincham, D. A., and Harvey, C.
M, (1991) Biochim Biophys. Acta 1070, 111-118). We have reexamined thi
s phenomenon separating the contribution of the two cationic amino aci
d transporters present in these cells (system y(+) and system y(+)L).
NaCl replacement with sucrose increased influx through system y(+)L, b
ut decreased influx through system y(+). We conclude that 1) the inhib
ition of system y(+) is a response to the membrane depolarization that
results from chloride removal, and 2) the stimulation of system y(+)L
is due to the enhancement of the negative surface potential. Consiste
ntly, lysine influx through system y(+)L (in sucrose medium) was reduc
ed by Na+, K+, Li+, and choline (K-0.5 = 25-34 mM), the effect reachin
g a maximum at 35-40% of the original flux. Divalent cations (Ca2+ and
Mg2+) were also inhibitory, but lower concentrations were required (K
-0.5 1.1-1.8 mM). The finding that sucrose stimulates uptake through c
hanges in the surface potential explains similar effects observed in o
ther cells with various cationic substrates.