Downregulated Cardiac Annexin VI mRNA and Protein Levels in Chronically Fibrillating Human Atria

Objectives: We compared the expression and distribution of atrial annexin VI between patients with atrial fibrillation (AF) or sinus rhythm (SR). Methods: Atrial appendages were obtained during cardiac surgery from 20 patients with chronic AF and 34 matched controls in SR. The expression and distribution of annexin VI were analyzed using semiquantitative RT-PCR, Western blotting and immunoconfocal microscopy. Results: In the AF group, compared to SR, the mRNA was reduced to <35% and the protein to <50% in amount (for each atrium, all p < 0.01). Immunoconfocal microscopy confirmed the downregulation of annexin VI protein in AF and demonstrated the colocalization of annexin VI with both Na⁺/Ca²⁺ exchangers and L-type Ca²⁺ channels in the sarcolemma, but not with ryanodine receptors in the sarcoplasmic reticulum. Conclusions: Atrial annexin VI, spatially colocalized with both Na⁺/Ca²⁺ exchangers and L-type Ca²⁺ channels in the myocyte membrane, is downregulated during chronic AF.