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Physiological Concept for a Blood Based CFTR Test

We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) could be involved in the volume regulation of human red blood cells (RBC). Experiments were based on two gadolinium (Gd3+) sensitive mechanisms, i.e. inhibition of ATP release (?ATPi) and membrane destabilization. RBC of either cystic fibrosis (CF) patients or healthy donors (non-CF) were exposed to KCl buffer containing Gd3+. A significantly larger quantity of non- CF RBC (2.55 %) hemolyzed as compared to CF RBC (0.89 %). It was found that both of the Gd3+ mechanisms simultaneously are needed to achieve hemolysis, since either overriding ?ATPi by exogenous ATP addition prevented Gd3+ induced hemolysis, or mimicking ?ATPi by apyrase in absence of Gd3+ could not trigger hemolysis. Additionally, ion driven volume uptake was found to be a prerequisite for Gd3+ induced hemolysis as chloride and potassium channel blockers reduced the Gd3+ response. The results show that in non-CF RBC Gd3+ exerts its dual effect leading to hemolysis. On the contrary, in CF RBC, lacking CFTR dependent ATP release, the sole Gd3+ effect of membrane destabilization is not sufficient to induce hemolysis similar to non-CF. This concept could form the basis of a novel method suitable for testing CFTR function in a blood sample.