高[Ｋ⁺]_oの条件下でイオノマイシンにより誘起されたラット唾液腺におけるＣａ^２+流入

抄録

An increases in extracellular K⁺ concentration ([K⁺]_o) inhibits Ca²⁺ entry in rat submandibular acinar cells. The high [K⁺]_o induced inhibition of TG-stimulated Ca²⁺ entry is thought to be induced by decreases in the driving force for Ca²⁺ entry. In the present study, we examined the effects of increasing [K⁺]_o on Ca²⁺ entry in TG-stimulated and ionomycin (IM)-stimulated rat submandibular acinar cells. Cells were first perfused with Ca²⁺-free control solution and were stimulated with TG (2 µM) for 10 min. Then Ca²⁺ (1.5 mM) was added (reintroduction of Ca²⁺). The introduction of Ca²⁺ increased [Ca²⁺]_i. Increases in [Ca²⁺]_i induced by the reintroduction of Ca²⁺ were examined in TG-stimulated submandibular acinar cells perfused with various [K⁺]_o. As increment of [K⁺]_o, [Ca²⁺]_i increases induced by the reintroduction of Ca²⁺ were suppressed. Similar experiments were performed using IM (5 µM). In IM-treated cells, the introduction of Ca²⁺ also increased [Ca²⁺]_i. However, as increment of [K⁺]_o, [Ca²⁺]_i increases induced by the reintroduction of Ca²⁺ were not suppressed. IM-induced [Ca²⁺]_i increases were also inhibited by Gd³⁺ (1 µM). The final [Ca²⁺]_is were similar in various [K⁺]_o, although the rate of [Ca²⁺]_i increase in the high K⁺ solution was slow compared with that in the control solution. The present study demonstrated that the driving force for Ca²⁺ entry is sufficient in the high K⁺ solution in rat submandibular acinar cells. A high K⁺ solution which depolarizes membrane potential appears to modulate Ca²⁺ entry pathways in rat submandibular acinar cells. [J Physiol Sci. 2007;57 Suppl:S128]