Properties of the Ca²⁺ influx reveal the duality of events underlying the activation by vanadate and fluoride of the Gárdos effect in human red blood cells

Abstract

. Substitution of Na + by K + inhibited the RS Ca 2+ influx induced by NaVO Q but stimulated that by NaF. The NaVO Qinduced Ca 2+ influx was sensitive to nifedipine (IC SH = 50 mol/l), Cu 2+ (IC SH = 9 mol/l), DTNB (5,5P-dithiobis-(dinitrobenzoic acid)) (IC SH = 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 RS Ca 2+ influx (IC SH = 21 mol/l and 28 mol/l, respectively). Pig RBC, known not to display the NaVO Qinduced Ca 2+ influx, exhibited Ca 2+ influx induced by NaF. The results show that NaVO Q 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 Ga èrdos effect induced by NaVO Q and NaF represents two phenomena activated by different mechanisms present in the cryptic state in the RBC membrane.z 1998 Federation of European Biochemical Societies.

Tetrodotoxin-sensitive Na + channels and muscarinic and purinergic receptors identified in human erythroid progenitor cells and red blood cell ghosts

“…The time course of the increase in Na ϩ permeability that occurs with exposure of human red blood cells to Ca 2ϩ plus CCh correlates with the time course (initial increase) of changes in Ca 2ϩ and cGMP content (41). Whether the pattern of these changes applies to the Ca 2ϩ plus F Ϫ case is not known although the transient increase in a TTX-sensitive Ca 2ϩ uptake has been correlated with the Na ϩ permeability changes (17). The implication here is that activation of muscarinic receptors by means of G proteins such as G i , G s , and G q , which are known to be present in human red blood cell membranes (8 -14), uses the same Na ϩ channels as does the activation by the combination Ca 2ϩ plus F Ϫ .…”

“…There is ample evidence that heterotrimeric G proteins of several types (e.g., G i , G o , G q ) are present in human red blood cells (8)(9)(10)(11)(12)(13)(14); in addition, these cells are also known to contain Ϸ2.7 M Al 3ϩ ͞l.rbc (15), which may be necessary for adenylyl cyclase activation (16). It was further shown that, under conditions where the Na ϩ flux was increased in the presence of added F Ϫ and Ca 2ϩ , Ca 2ϩ uptake (measured with 45 Ca 2ϩ ) was also increased and could be inhibited with TTX (17). A similar TTX-sensitive Ca 2ϩ influx has been characterized in cardiac myocytes (18).…”