Increased sodium–proton antiporter activity in patients with obstructive sleep apnoea
Cytosolic pH (pHi) and the activity of the sodium–proton antiporter (Na+/H+ antiporter) were measured in lymphocytes from 22 patients with obstructive sleep apnoea and from 24 age-matched healthy subjects (Controls). The cellular Na+/H+ antiporter was measured spectrophotometrically using a pH-sensitive fluorescent dye after intracellular acidification using sodium propionate. Resting pHi was similar in lymphocytes from patients with obstructive sleep apnoea and from controls (7.36 ± 0.20, n=22; vs. 7.35 ± 0.19, n=24; mean ± SD). The Na+/H+ antiporter activity was significantly higher in patients with obstructive sleep apnoea than in controls (11.87 ± 3.26 × 10–3 pHi/s vs. 4.38 ± 1.40 × 10–3 pHi/s; P < 0.0001). The apparent affinity of the Na+/H+ antiporter was not significantly different between the groups (6.90 ± 0.23 vs. 6.87 ± 0.20). In patients with obstructive sleep apnoea the activity of the Na+/H+ antiporter remained stable during the night. The activity of the Na+/H+ antiporter was 13.49 ± 4.80 × 10–3 pHi/s at 20.00 and 13.26 ± 6.13 × 10–3 pHi/s at 02.00. From the present results it is concluded that an increased cellular Na+/H+ antiporter activity may be a genetic marker for patients who are predisposed to obstructive sleep apnoea.
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