Ca(2+)-induced Ca(2+) release activates spontaneous miniature outward currents (SMOCs) in parasympathetic cardiac neurons.
Ca(2+)-induced Ca(2+) release activates spontaneous miniature outward currents (SMOCs) in parasympathetic cardiac neurons.
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DOI：
10.1152/jn.1999.82.2.540
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发表时间：
1999-08
影响因子：
2.5
通讯作者：
L. A. Merriam;F. Scornik;R. Parsons
中科院分区：
文献类型：
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作者：
L. A. Merriam;F. Scornik;R. Parsons
Mudpuppy副交感心脏神经元表现出自发的微型外向电流（smoc），这被认为是由于Ca（2+）从靠近质膜的内部储存中局部释放，激活了大电导Ca（2+）激活的K（+）通道（BK通道）簇。通过穿孔补片全细胞记录来确定Ca（2+）诱导的Ca（2+）释放（CICR）是否参与了SMOC的产生。通过100 nM的iberiotoxin或500 μ m的tetraethylamium （TEA）抑制smoc，而100 nM的apamin则不抑制smoc，我们证实了BK通道的参与。在含有0 Ca(2+)/3.6 mM Mg（2+）的溶液中，以及在存在1微米硝苯地平和3微米ω - concontoxin GVIA的情况下，SMOC频率降低，这表明SMOC激活依赖于钙内流。然而，仅Ca（2+）内流是不够的；SMOC的激活也依赖于对咖啡因和ryanodine敏感的Ca（2+）储存中Ca（2+）的释放，因为暴露于2 mM咖啡因持续导致SMOC频率增加，10-100微米ryanodine改变了SMOC的结构并最终抑制了SMOC活性。细胞内Ca（2+）储存被Ca- atp酶抑制剂环吡唑酸（10微米）耗尽，即使Ca（2+）内流没有受到损害，也会抑制SMOC活性。我们还测试了膜渗透性Ca（2+）螯合剂，双-（邻氨基酚氧基）-N，N，N‘， N’-四乙酸-am （BAPTA-AM）和EGTA-AM的效果。EGTA-AM（10微米）对SMOC的激活没有抑制作用，而10微米的BAPTA-AM对SMOC的激活有抑制作用。在SMOC被BAPTA完全抑制后，3mm咖啡因使SMOC活性恢复。这种效应在去除咖啡因时是可逆的，这表明触发内部Ca（2+）释放通道的Ca（2+）来源与激活BK通道簇的Ca（2+）来源不同。我们提出，通过电压依赖性Ca（2+）通道的Ca（2+）内流是SMOC生成所必需的，但Ca（2+）内流触发细胞内储存的CICR，然后激活负责SMOC生成的BK通道。
Mudpuppy parasympathetic cardiac neurons exhibit spontaneous miniature outward currents (SMOCs) that are thought to be due to the activation of clusters of large conductance Ca(2+)-activated K(+) channels (BK channels) by localized release of Ca(2+) from internal stores close to the plasma membrane. Perforated-patch whole cell recordings were used to determine whether Ca(2+)-induced Ca(2+) release (CICR) is involved in SMOC generation. We confirmed that BK channels are involved by showing that SMOCs are inhibited by 100 nM iberiotoxin or 500 microM tetraethylammonium (TEA), but not by 100 nM apamin. SMOC frequency is decreased in solutions that contain 0 Ca(2+)/3.6 mM Mg(2+), and also in the presence of 1 microM nifedipine and 3 microM omega-conotoxin GVIA, suggesting that SMOC activation is dependent on calcium influx. However, Ca(2+) influx alone is not sufficient; SMOC activation is also dependent on Ca(2+) release from the caffeine- and ryanodine-sensitive Ca(2+) store, because exposure to 2 mM caffeine consistently caused an increase in SMOC frequency, and 10-100 microM ryanodine altered the configuration of SMOCs and eventually inhibited SMOC activity. Depletion of intracellular Ca(2+) stores by the Ca-ATPase inhibitor cyclopiazonic acid (10 microM) inhibited SMOC activity, even when Ca(2+) influx was not compromised. We also tested the effects of the membrane-permeable Ca(2+) chelators, bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid-AM (BAPTA-AM) and EGTA-AM. EGTA-AM (10 microM) caused no inhibition of SMOC activation, whereas 10 microM BAPTA-AM consistently inhibited SMOCs. After SMOCs were completely inhibited by BAPTA, 3 mM caffeine caused SMOC activity to resume. This effect was reversible on removal of caffeine and suggests that the source of Ca(2+) that triggers the internal Ca(2+) release channel is different from the source of Ca(2+) that activates clusters of BK channels. We propose that influx of Ca(2+) through voltage-dependent Ca(2+) channels is required for SMOC generation, but that the influx of Ca(2+) triggers CICR from intracellular stores, which then activates the BK channels responsible for SMOC generation.