Sickle cell disease, a highly debilitating disease affecting millions worldwide, is caused by the homozygous inheritance of the mutant haemoglobin S (HbS), a malaria-stabilized gene conferring protection against lethal cerebral malaria. When sickle red blood cells traverse deoxygenated bloodstreams, HbS rapidly nucleates into polymers that keep the sickle cell Piezo1 channels open for the duration of deoxy transits. On transition to oxy streams, Piezo1 channels close immediately and remain closed. Downgradient ion fluxes ("leaks") through open deoxy-Piezo1 channels change the intracellular concentrations of Ca2+, K+ and Na+ in sickle cells stimulating balancing counter-fluxes via the calcium (PMCA) and Na/K (ATP1) membrane pumps. This sets up a complex Ca2+, Na+ and K+ pump-leak flux-dynamics in the sickle cells. The current investigation is focused on the magnitude, kinetics, and implications of the pump-leak fluxes induced by deoxy-Piezo1 channels on the pathophysiology of sickle cell disease. Model simulations were used to compare and contrast the pump-leak calcium flux-patterns of normal and sickle red blood cells. The results predicted a unique kinetic pattern for the pump-leak calcium fluxes in deoxy sickle cells: a sharp calcium influx peak on capillary ingress followed by a near-zero net calcium flux for the duration of deoxy transits, masking large unidirectional and energy consuming pump-leak calcium fluxes. The same pattern applied to pump-leak Na+ and K+ fluxes, with particular intensity in the irreversibly sickled cells. Estimates of ATP turnover and lactate production rates associated with pump-leak Ca2+, Na+ and K+ fluxes were found to be substantially increased above those in normal, oxy or deoxy RBCs or in oxy sickle RBCs. These results opened the possibility that pump mediated increased ATP turnover in deoxy sickle cells contribute significantly to lactate production and metabolic acidosis in sickle cell disease.
Lew et al. (Wed,) studied this question.