A slowly inactivating calcium current works as a calcium sensor in calcitonin‐secreting cells

[摘要]

Calcitonin (CT)-secreting cells (C-cells) are remarkably sensitive to changes in the extracellular Ca²⁺ concentration. In order to detect the mechanism by which C-cells monitor Ca²⁺, we compared a C-cell line responding to Ca²⁺ (rMTC cells) with another one known to have a defect in this Ca²⁺ signal transduction (TT cells). Rises of the Ca²⁺ concentration caused rMTC cells to depolarize and/or elicited spontaneous action potentials. Under voltage-clamp conditions, rMTC cells showed a slowly decaying Ca²⁺ inward current which was sensitive to dihydropyridines but not to Ni²⁺ at a low concentration. In contrast, the ‘defective’ TT cells neither depolarized nor fired action potentials with high Ca²⁺; they only exhibited an Ni²⁺-sensitive, transient Ca²⁺ current. The data strongly suggest that the slowly inactivating Ca²⁺ current is a prerequisite for Ca²⁺-sensitivity of C-cells and that fast inactivating channels are not sufficient to act as sensors of the extracellular Ca²⁺ concentration.

[学科分类] 生物化学/生物物理

[关键词] Calcitonin-secreting cell;rMTC cell;TT cell;Calcium current