Su Zhi, Sheets Michael, Ishida Hideyuki, Li Fenghua, Barry William H
Cardiology Division, University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
J Pharmacol Exp Ther. 2004 Jan;308(1):324-9. doi: 10.1124/jpet.103.056564. Epub 2003 Oct 17.
Saxitoxin (STX) and tetrodotoxin (TTX) are frequently used to selectively block sodium channels. In this study, we provide evidence that commercial STX also inhibits L-type Ca2+ currents (I(Ca,L)) in adult mouse ventricular myocytes (VMs) and tsA-201 cells that were transiently cotransfected with three calcium channel subunits. We measured inhibition of sodium currents (INa) in mouse VMs, of I(Ca,L) in mouse VM and tsA-201 cells, and intracellular calcium concentration ([Ca2+]i) transients in single mouse VMs. STX or TTX was abruptly applied before the test voltage pulse using a rapid solution switcher device. STX (10 microM; Calbiochem) and TTX (60 microM; Sigma-Aldrich) completely blocked INa in mouse VMs. However, STX at 10 microM also reduced I(Ca,L) in mouse VM by 39% (P < 0.0001; n = 14), whereas TTX at 60 microM had no effect on I(Ca,L). STX (10 microM; Calbiochem) reduced the amplitude of the [Ca2+]i transients in mouse VMs by 36% (P < 0.0001; n = 10). In contrast, TTX (60 microM; Sigma-Aldrich) only reduced the amplitude of the [Ca2+]i transients by 9% (P = 0.003; n = 5). STX (10 microM) obtained from Sigma-Aldrich showed a similar inhibitory effect on I(Ca,L) (33%) (P < 0.0001; n = 5) in mouse VMs. STX (Calbiochem) inhibited the calcium currents of tsA-201 cells in a dose-dependent manner. This inhibition was voltage-independent. The current-voltage relationship of calcium currents in tsA-201 cells was not altered by STX. These results indicate that STX partially blocks L-type Ca2+ channels and thus provide further evidence that its effects are not specific for Na+ channels.
石房蛤毒素（STX）和河豚毒素（TTX）常被用于选择性阻断钠通道。在本研究中，我们提供证据表明，市售的STX还能抑制成年小鼠心室肌细胞（VMs）以及瞬时共转染了三个钙通道亚基的tsA - 201细胞中的L型钙电流（I(Ca,L)）。我们测量了小鼠VMs中的钠电流（INa）抑制情况、小鼠VM和tsA - 201细胞中的I(Ca,L)抑制情况以及单个小鼠VMs中的细胞内钙浓度（[Ca2+]i）瞬变情况。使用快速溶液切换装置在测试电压脉冲之前突然施加STX或TTX。STX（10微摩尔；Calbiochem）和TTX（60微摩尔；Sigma - Aldrich）完全阻断了小鼠VMs中的INa。然而，10微摩尔的STX也使小鼠VM中的I(Ca,L)降低了39%（P < 0.0001；n = 14），而60微摩尔的TTX对I(Ca,L)没有影响。STX（10微摩尔；Calbiochem）使小鼠VMs中[Ca2+]i瞬变的幅度降低了36%（P < 0.0001；n = 10）。相比之下，TTX（60微摩尔；Sigma - Aldrich）仅使[Ca2+]i瞬变的幅度降低了9%（P = 0.003；n = 5）。从Sigma - Aldrich获得的STX（10微摩尔）对小鼠VMs中的I(Ca,L)也显示出类似的抑制作用（33%）（P < 0.0001；n = 5）。STX（Calbiochem）以剂量依赖的方式抑制tsA - 201细胞的钙电流。这种抑制与电压无关。STX并未改变tsA - 201细胞中钙电流的电流 - 电压关系。这些结果表明，STX部分阻断L型钙通道，从而进一步证明其作用并非对钠通道具有特异性。
