Properties of the Ca 2+ influx reveal the duality of events underlying the activation by vanadate and fluoride of the Gárdos effect in human red blood cells

Abstract

The properties of the 45Ca 2+ influx by human red blood cells (RBC) induced by NaVO 3 or NaF were compared. The NaVO 3-induced 45Ca 2+ influx was slower and less extensive than that induced by NaF. Both processes were saturable with Ca 2+. Substitution of Na + by K + inhibited the 45Ca 2+ influx induced by NaVO 3 but stimulated that by NaF. The NaVO 3-induced Ca 2+ influx was sensitive to nifedipine (IC 50=50 mol/l), Cu 2+ (IC 50=9 mol/l), DTNB (5,5′-dithiobis-(dinitrobenzoic acid)) (IC 50=12 mol/l) (maximal inhibition 16%, 18%, and 28%, respectively, if NaF was used as inducer). On the other hand, tetrodotoxin (TTX) and cyclosporin A inhibited only the NaF-induced 45Ca 2+ influx (IC 50=21 mol/l and 28 mol/l, respectively). Pig RBC, known not to display the NaVO 3-induced Ca 2+ influx, exhibited Ca 2+ influx induced by NaF. The results show that NaVO 3 activates the Ca 2+ influx via a pathway homologous to the L-type Ca 2+ channel while the NaF-induced Ca 2+ influx is mediated via the TTX-sensitive Na + channel in the presence of NaF with possible participation of calcineurin or cyclophilin. Thus, the Gárdos effect induced by NaVO 3 and NaF represents two phenomena activated by different mechanisms present in the cryptic state in the RBC membrane.