Dynamic Regulation of Cell Volume and Extracellular ATP of Human Erythrocytes

Abstract

IntroductionThe peptide mastoparan 7 (MST7) triggered in human erythrocytes (rbcs) the release of ATP and swelling. Since swelling is a well-known inducer of ATP release, and extracellular (ATPe), interacting with P (purinergic) receptors, can affect cell volume (Vr), we explored the dynamic regulation between Vr and ATPe.Methods and TreatmentsWe made a quantitative assessment of MST7-dependent kinetics of Vr and of [ATPe], both in the absence and presence of blockers of ATP efflux, swelling and P receptors.ResultsIn rbcs 10 μM MST7 promoted acute, strongly correlated changes in [ATPe] and Vr. Whereas MST7 induced increases of 10% in Vr and 190 nM in [ATPe], blocking swelling in a hyperosmotic medium + MST7 reduced [ATPe] by 40%. Pre-incubation of rbcs with 10 μM of either carbenoxolone or probenecid, two inhibitors of the ATP conduit pannexin 1, reduced [ATPe] by 40–50% and swelling by 40–60%, while in the presence of 80 U/mL apyrase, an ATPe scavenger, cell swelling was prevented. While exposure to 10 μM NF110, a blocker of ATP-P2X receptors mediating sodium influx, reduced [ATPe] by 48%, and swelling by 80%, incubation of cells in sodium free medium reduced swelling by 92%.Analysis and DiscussionResults were analyzed by means of a mathematical model where ATPe kinetics and Vr kinetics were mutually regulated. Model dependent fit to experimental data showed that, upon MST7 exposure, ATP efflux required a fast 1960-fold increase of ATP permeability, mediated by two kinetically different conduits, both of which were activated by swelling and inactivated by time. Both experimental and theoretical results suggest that, following MST7 exposure, ATP is released via two conduits, one of which is mediated by pannexin 1. The accumulated ATPe activates P2X receptors, followed by sodium influx, resulting in cell swelling, which in turn further activates ATP release. Thus swelling and P2X receptors constitute essential components of a positive feedback loop underlying ATP-induced ATP release of rbcs.

Induction of ATP Release, PPIX Transport, and Cholesterol Uptake by Human Red Blood Cells Using a New Family of TSPO Ligands

“…RBCs play a fundamental role in the tissue oxygen supply, via the controlled release of ATP in the areas of increased oxygen need [ 34 ] ATP exit can be achieved by hemolysis or by regulated mechanisms mediated by transporters, channels, or pores [ 27 , 32 , 33 , 35 , 36 , 37 ]. Among the latter is pannexin-1, a protein thought to arrange in homohexameric pores capable of allowing the transport of ATP across the plasma membrane [ 38 ].…”

Erythrocyte’s aging in microgravity highlights how environmental stimuli shape metabolism and morphology

“…The mechanical stimulation provided by the 3D-clinostat acts as a major environmental accelerator of the RBCs’ aging and activates distinctive metabolic and morphological patterns compared to standard aging. In addition the stimulation is of sufficient magnitude to induce physiological phenomena, such as the expulsion of ATP, which is activated by overcoming a threshold of mechanical deformation 2 , 3 and that, according to recent data 47 , could be stronger in the presence of environmental mechanical stresses or solicitations.…”

The Erythrocytic Hypothesis of Brain Energy Crisis in Sporadic Alzheimer Disease: Possible Consequences and Supporting Evidence

“…For instance, in AD patients RBCs have been found to exhibit morphological changes [46,47], leading to decreased deformability [48], perturbations in the physical state of membrane proteins [49,50], and oxidant/antioxidant equilibrium [51][52][53][54]. These changes are in some way due to the destabilization of intracellular metabolism in erythrocytes [55][56][57][58]. However, the mechanisms underlying the foregoing alterations in RBC metabolism in AD patients are not fully understood.…”