Ca²⁺ influx induced by ionomycin under a high [K⁺]_o in rat submandibular acinar cells

Abstract

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]