An Experimental Study

Rationale: Understanding the physiology of CO₂ stores mobilization is a prerequisite for intermittent extracorporeal CO₂ removal (ECCO₂R) in patients with chronic hypercapnia.Objectives: To describe the dynamics of CO₂ stores.Methods: Fifteen pigs (61.7 ± 4.3 kg) were randomized to 48 hours of hyperventilation (group "Hyper," n = 4); 48 hours of hypoventilation (group "Hypo," n = 4); 24 hours of hypoventilation plus 24 hours of normoventilation (group "Hypo-Baseline," n = 4); or 24 hours of hypoventilation plus 24 hours of hypoventilation plus ECCO₂R (group "Hypo-ECCO₂R," n = 3). Forty-eight hours after randomization, the current [Formula: see text]e was reduced by 50% in every pig.Measurements and Main Results: We evaluated [Formula: see text]co₂, [Formula: see text]o₂, and metabolic [Formula: see text]co₂ ([Formula: see text]o₂ times the metabolic respiratory quotient). Changes in the CO₂ stores were calculated as [Formula: see text]co₂ - metabolic V̇co₂. After 48 hours, the CO₂ stores decreased by 0.77 ± 0.17 l kg^-1 in group Hyper and increased by 0.32 ± 0.27 l kg^-1 in group Hypo (P = 0.030). In group Hypo-Baseline, they increased by 0.08 ± 0.19 l kg^-1, whereas in group Hypo-ECCO₂R, they decreased by 0.32 ± 0.24 l kg^-1 (P = 0.197). In the second 24-hour period, in groups Hypo-Baseline and Hypo-ECCO₂R, the CO2 stores decreased by 0.15 ± 0.09 l kg^-1 and 0.51 ± 0.06 l kg^-1, respectively (P = 0.002). At the end of the experiment, the 50% reduction of [Formula: see text]e caused a Pa_CO2 rise of 9.3 ± 1.1, 32.0 ± 5.0, 16.9 ± 1.2, and 11.7 ± 2.0 mm Hg h^-1 in groups Hyper, Hypo, Hypo-Baseline, and Hypo-ECCO₂R, respectively (P < 0.001). The Pa_CO2 rise was inversely related to the previous CO₂ stores mobilization (P < 0.001).Conclusions: CO₂ from body stores can be mobilized over 48 hours without reaching a steady state. This provides a physiological rationale for intermittent ECCO₂R in patients with chronic hypercapnia.

ORAI2 Down-Regulation Potentiates SOCE and Decreases Aβ42 Accumulation in Human Neuroglioma Cells

Senile plaques, the hallmarks of Alzheimer's Disease (AD), are generated by the deposition of amyloid-beta (Aβ), the proteolytic product of amyloid precursor protein (APP), by β and γ-secretase. A large body of evidence points towards a role for Ca²⁺ imbalances in the pathophysiology of both sporadic and familial forms of AD (FAD). A reduction in store-operated Ca²⁺ entry (SOCE) is shared by numerous FAD-linked mutations, and SOCE is involved in Aβ accumulation in different model cells. In neurons, both the role and components of SOCE remain quite obscure, whereas in astrocytes, SOCE controls their Ca²⁺-based excitability and communication to neurons. Glial cells are also directly involved in Aβ production and clearance. Here, we focus on the role of ORAI2, a key SOCE component, in modulating SOCE in the human neuroglioma cell line H4. We show that ORAI2 overexpression reduces both SOCE level and stores Ca²⁺ content, while ORAI2 downregulation significantly increases SOCE amplitude without affecting store Ca²⁺ handling. In Aβ-secreting H4-APPswe cells, SOCE inhibition by BTP2 and SOCE augmentation by ORAI2 downregulation respectively increases and decreases Aβ42 accumulation. Based on these findings, we suggest ORAI2 downregulation as a potential tool to rescue defective SOCE in AD, while preventing plaque formation.