機能亢進状態のヒト副甲状腺細胞において生理的なカルシウム濃度上昇で活性化されるジヒドロピリジン感受性カルシウム流入

抄録

In the companion abstract, we showed that cardiac-like L-type Ca²⁺ channel is expressed in hyperparathyroid cells. We then posed the question whether this channel could be activated under physiological conditions. Cytoplasmic Ca²⁺ concentration was measured with a Ca²⁺-sensitive fluorescent indicator probe, fluo-3. The cells were immersed in Hepes-buffered solution containing 1-2 mM Ca²⁺. Local application of the same solution via a small-tipped pipette resulted in no change in the fluo-3 fluorescence, suggesting that stretch-activated Ca²⁺ permeable channels were not activated under our experimental conditions . When Ca²⁺ concentration of the pipette solution was raised to 2.5-3 mM, however, application of the high Ca²⁺ solution for 10 s evoked a transient increase in fluo-3 fluorescence (a fluo-3 transient). In the presence of 10 μM nitrendipine, the fluo-3 transient was markedly reduced. These results could be explained by the hypothesis that increase in extracellular Ca²⁺ concentration induces Ca²⁺ entry, at least in part, through the dihydropyridine-sensitive L-type Ca²⁺ channels. In addition, neither skeletal myotubes nor cardiac myocytes showed fluo-3 transients upon exposure to 10 mM extraccelular Ca²⁺. [Jpn J Physiol 55 Suppl:S209 (2005)]