Voltage-Dependent Calcium Channels in Young and Old Human Red Cells

Abstract

Presence of subtypes of voltage-dependent Ca channels was investigated in young and old human red cells, employing immunological and flux-kinetics methods. Western blots showed specific reaction toward polyclonal rabbit antibodies raised against a highly conserved residue of alpha1 subunit of high-voltage activated Ca channels (pan alpha1) and against conserved residues of alpha1C and alpha1E subunits. No specific reaction was detected with antibodies against conserved residues of alpha1A, alpha1B, or alpha1D subunits. Only a single band (approx 260 kDa) was revealed on anti-pan alpha1 or anti-alpha1E blots, whereas two bands (200 and 230 kDa) were detected by anti-alpha1C exposure. Blots from old cells always showed diminished band intensity. Channel activity was assessed by studying the effect of voltage-dependent Ca channels blockers under conditions likely to alter the red cell membrane potential, through incubation in media of different composition. In a 150 mM NaCl + 5 mM KCl medium, blockers of L-, R-, and Q-type caused a 15-50% reduction of 45Ca influx into cells, which had the Ca pump inactivated by either exhaustive adenosine triphosphate depletion or presence of vanadate plus substrates. Additionally, some P/Qand N-type blockers also reduced Ca influx to various extents (25-60%). Old cells were generally insensitive to L-type but not to non-L-type blockers. Raising external K to about 70-80 mM reduced by 50-100% inhibition by L-type blockers. Incubation in a gluconate medium containing 150 mM Na+5 mM K practically abolished the action of L-type blockers, but only slightly reducing that by non-L-type. The results clearly demonstrate presence of L- and R-type Ca channels, apparently occurring in different functional states in young and old cells. Other non-L-type channels were also demonstrated only by pharmacological means. A possible physiological role for these channels is discussed.

Nitroprusside inhibits calcium‐induced impairment of red blood cell deformability

“…The dominant effect involves the activation of calcium influx through native calcium channels. Although their study did not involve RBCs, there is evidence of similar calcium channels in RBCs 47‐50. Taking this study into account, the SNP inhibition of calcium influx and activation of the Gardos channel may involve inhibition of these native calcium channels.…”

Functional plasticity of the N-methyl-d-aspartate receptor in differentiating human erythroid precursor cells

“…However, Cheung et al (8) have reported that Ca 2+ influx induced by Epo was insufficient to activate Ca 2+ -sensitive K + channels (Gardos channel). This strongly indicates the presence of multiple Ca 2+ uptake pathways in EPCs during differentiation (52). We have recently reported the presence of N -methyl- d -aspartate receptors (NMDARs) in human progenitor cells and have shown that these nonselective, ligand-gated cation channels mediate Ca 2+ uptake in EPCs (18, 35).…”

Patch-Clamp Analysis of Membrane Transport in Erythrocytes

“…Nevertheless, a few studies have given evidence that true Ca 2+ channels might also be present in the RBCs membrane. Even if the data regarding the exact nature of the Ca 2+ pathway are confusing, the presence of both L-type and R-type Ca 2+ channels subunits in RBCs membrane has been detected using western blots and tracers fluxes with adapted inhibitors (Romero et al, 2006). The group of Pedro Romero has also shown that the channel types appear to be different according to the RBC age.…”