PPADS, a P2X receptor antagonist, as a novel inhibitor of the reverse mode of the Na⁺/Ca²⁺ exchanger in guinea pig airway smooth muscle

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• 作者：Edgar Flores-Soto^a ; Jorge Reyes-Garcí ; a^a ; Bettina Sommer^b ; Jaime Chavez^b ; Carlos Barajas-Ló ; pez^c ; Luis M. Montañ ; o^a ; ^{lmmr@servidor.unam.mx}
• 关键词：PPADS ; KB-R7943 ; Airway smooth muscle ; Na+/Ca2+ exchanger
• 刊名：European Journal of Pharmacology
• 出版年：2012
• 出版时间：15 January, 2012
• 年：2012
• 卷：674
• 期：2-3
• 页码：439-444
• 全文大小：1439 K

文摘

The Na⁺/Ca²⁺exchanger (NCX) principal function is taking 1 Ca²⁺ out of the cytoplasm and introducing 3 Na⁺. The increase of cytoplasmic Na⁺ concentration induces the NCX reverse mode (NCX_REV), favoring Ca²⁺ influx. NCX_REV can be inhibited by: KB-R7943 a non-specific compound that blocks voltage-dependent and store-operated Ca²⁺ channels; SEA0400 that appears to be selective for NCX_REV, but difficult to obtain and SN-6, which efficacy has been shown only in cardiomyocytes. We found that PPADS, a P2X receptor antagonist, acts as a NCX_REV inhibitor in guinea pig tracheal myocytes. In these cells, we characterized the NCX_REV by substituting NaCl and NaHCO₃ with LiCl, resulting in the increase of the intracellular Ca²⁺ concentration ([Ca²⁺]i) using fura 2-AM. We analyzed 5 consecutive responses of the NCX_REV every 10 min, finding no differences among them. To evaluate the effect of different NCX_REV blockers, concentration response curves to KB-R7943 (1, 3.2 and 10 ¦ÌM), and SN-6 (3.2, 10 and 30 ¦ÌM) were constructed, whereas PPADS effect was characterized as time- and concentration-dependent (1, 3.2, 10 and 30 ¦ÌM). PPADS had similar potency and efficacy as KB-R7943, whereas SN-6 was the least effective. Furthermore, KCl-induced contraction, sensitive to D600 and nifedipine, was blocked by KB-R7943, but not by PPADS. KCl-induced [Ca²⁺]i increment in myocytes was also significantly decreased by KBR-7943 (10 ¦ÌM). Our results demonstrate that PPADS can be used as a reliable pharmacological tool to inhibit NCX_REV, with the advantage that it is more specific than KB-R7943 because it does not affect L-type Ca²⁺ channels.