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Buffering Contribution of Mitochondria to the [Ca<SUP>2+</SUP>]<SUB>i</SUB> Increase by Ca<SUP>2+</SUP> Influx through Background Nonselective Cation Channels in Rabbit Aortic Endothelial Cells

Buffering Contribution of Mitochondria to the [Ca<SUP>2+</SUP>]<SUB>i</SUB> Increase by Ca<SUP>2+</SUP> Influx through Background Nonselective Cation Channels in Rabbit Aortic Endothelial Cells

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To prove the buffering contribution of mitochondria to the increase of intracellular Ca<SUP>2+</SUP> level ([Ca<SUP>2+</SUP>]<SUB>i</SUB>) via background nonselective cation channel (background NSCC), we examined whether inhibition of mitochondria by protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP) affects endothelial Ca<SUP>2+</SUP> entry and Ca<SUP>2+</SUP> buffering in freshly isolated rabbit aortic endothelial cells (RAECs). The ratio of fluorescence by fura-2 AM (R<SUB>340/380</SUB>) was measured in RAECs. Biological state was checked by application of acetylcholine (ACh) and ACh (10μM) increased R<SUB>340/380</SUB> by 1.1&#8273;0.15 (mean&#8273;S.E., n=6). When the external Na<SUP>+</SUP> was totally replaced by NMDG<SUP>+</SUP>, R<SUB>340/380</SUB> was increased by 1.19&#8273;0.17 in a reversible manner (n=27). NMDG<SUP>+</SUP>-induced [Ca<SUP>2+</SUP>]<SUB>i</SUB> increase was followed by oscillatory decay after [Ca<SUP>2+</SUP>]<SUB>i</SUB> reached the peak level. The increase of [Ca<SUP>2+</SUP>]<SUB>i</SUB> by NMDG<SUP>+</SUP> was completely suppressed by replacement with Cs<SUP>+</SUP>. When 1μM CCCP was applied to bath solution, the ratio of [Ca<SUP>2+</SUP>]<SUB>i</SUB> was increased by 0.4&#8273;0.06 (n=31). When 1μM CCCP was used for pretreatment before application of NMDG<SUP>+</SUP>, oscillatory decay of [Ca<SUP>2+</SUP>]<SUB>i</SUB> by NMDG<SUP>+</SUP> was significantly inhibited compared to the control (p<0.05). In addition, NMDG<SUP>+</SUP>-induced increase of [Ca<SUP>2+</SUP>]<SUB>i</SUB> was highly enhanced by pretreatment with 2μM CCCP by 320&#8273;93.7%, compared to the control (mean&#8273;S.E., n=12). From these results, it is concluded that mitochondria might have buffering contribution to the [Ca<SUP>2+</SUP>]<SUB>i</SUB> increase through regulation of the background NSCC in RAECs.

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