Single-channel activity and expression of atrial L-type Ca2+ channels in patients with latent hyperthyroidism

Departments of 1 Pharmacology, 2 Nuclear Medicine, and 3 Cardiothoracic Surgery, University of Cologne, 50931 Cologne; 4 Department of Pharmacology, University of Münster, 48149 Münster; and 5 Medizinische Poliklinik, University of Bonn, 53105 Bonn, Germany Patients with "latent hyperthyroidism" (suppressed thyroid-stimulating hormone and normal circulating thyroid hormones) are at risk to develop atrial fibrillation. In animal models, hyperthyroidism is associated with increased cardiac L-type Ca 2+ current. Therefore, we assessed L-type channel function and expression in right atria from patients undergoing cardiac surgery. Single L-type channels were studied in the cell-attached condition. Voltage dependence of gating was similar in patients with and without latent hyperthyroidism. With use of a pulse protocol leading to maximum channel availability, single-channel activity was further analyzed. Average peak current was significantly enhanced in latent hyperthyroidism, mainly because of an increased channel availability ( P