Functional coupling of the exchanger with Ca²⁺ release from intracellular stores in cultured smooth muscle cells of guinea pig ileum

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• 作者：Ohata ; Hisayuki ; Kawanishi ; Toru ; Hisamitsu ; Takashi ; Takahashi ; Michihito ; Momose ; Kazutaka
• 关键词：cultured smooth muscle cells ; intracellular Ca²⁺ store ; Ca²⁺ release ; exchanger
• 刊名：Life Sciences
• 出版年：1996
• 出版时间：March 1, 1996
• 年：1996
• 卷：58
• 期：14
• 页码：1179-1187
• 全文大小：620 K

文摘

The mechanism of increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) by removal of extracellular Na⁺, which phenomena were reported previously (Japan. J. Pharmacol.63 83-91 1993), was investigated in cultured guinea pig ileum longitudinal muscle cells loaded with a fluorescent Ca²⁺ indicator, fura-2, by digital ratio imaging microscopy. Isotonic substitution of choline chloride for NaCl induced a transient increase in [Ca²⁺]_i. The pretreatment of thapsigargin (0.5 μM), but not nicardipine (10 μM), suppressed the transient increase completely. In solutions containing micromolar concentrations of free Ca²⁺ (nominally Ca²⁺-free solution), the Na⁺-free induced transient increase was observed, but neither the second cell exposure to the Na⁺-free solution nor the following application of histamine increased [Ca²⁺]_i, indicating that removal of extracellular Na⁺ releases Ca²⁺ from intracellular stores including inositol 1,4,5-trisphosphate (IP₃)-releasable pools. The Na⁺-free-induced transient increase required the presence of more than micromolar concentrations of extracellular free Ca²⁺ and releasable Ca²⁺ within the stores, but ryanodine did not affect the transient increase. These results suggest that undetectable influx of Ca²⁺ by the reverse-mode action of the exchanger can release Ca²⁺ from the thapsigargin-sensitive intracellular stores including IP₃-releasable pools.