A [Na+]o-independent, pHo-dependent mechanism for reduction of intracellular [Ca2+] after influx through Ca2+ channels in mouse pituitary cells.
A [Na+]o-independent, pHo-dependent mechanism for reduction of intracellular [Ca2+] after influx through Ca2+ channels in mouse pituitary cells.
复制标题
小鼠垂体细胞中通过 Ca2 通道流入后细胞内 [Ca2] 减少的不依赖于 [Na ]o 且 pHo 依赖的机制。
DOI：
10.1085/jgp.98.5.893
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
Horn,R
中科院分区：
文献类型：
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作者：
Korn,SJ;Horn,R
研究了细胞外pH(Pho)对钙依赖氯电流(ICT~c.)在电压钳ATT-20垂体细胞上进行了研究。在-20 mV至+60 mV电压范围内，通过阶跃去极化开放质膜钙通道，激活ICl~c。PH 0从7.3增加到8.0，在含Na+和无Na+溶液中的细胞穿孔膜片记录的尾电流可逆地延长。当吸管溶液含有0.5 mM EGTA时，这种延长在标准的全细胞记录中被阻止。细胞内pH为7.3、HEPES浓度为80 mM时，尾流仍有延长，因此PHO升高不是由于细胞内pH的改变所致。在尾流过程中，当尾流过程中pH o迅速变化时，在关闭所有的钙通道后，尾电流延长，因此在pho8处的Ic，C的延长不能解释为对钙通道的直接作用。在全细胞记录中，当细胞内钙离子浓度([Ca~(2+)]i)被EGTA固定时，改变pH为8并不能延长Cl-尾电流，因此增加pho对IC~c~的影响也不能用对C_1-通道的直接作用来解释。然而，提高pho确实延长了去极化引起的[Ca~(2+)]i瞬变，这是用钙指示剂Fura-2直接测量的。综上所述，这些数据表明，在通过钙通道内流后，存在一种Na+非依赖的、对光敏感的机制来降低[Ca+]~+。这一机制与质膜有关，并在与这些细胞中单动作电位持续时间相关的时间尺度上活跃。我们认为这种作用机制可能是质膜Ca+-ATPase。
The effect of extracellular pH (pHo) on the duration of calciumdependent chloride currents (Ict~ c.) was studied in voltage clamped AtT-20 pituitary cells. Icl~ c., was activated by Ca*+ influx through plasma membrane Ca 2+ channels, which were opened by step depolarization to voltages between-20 and+ 60 mV. Increasing pH o from 7.3 to 8.0 reversibly prolonged Icl~ c., tail currents in perforated patch recordings from cells bathed in both Na+-containing and Na+-free solutions. This prolongation was prevented in standard whole cell recordings when the pipette solution contained 0.5 mM EGTA. The effects of raised pHo were not due to alteration of intracellular pH, since tail current prolongation still occurred when intracellular pH was buffered at 7.3 with 80 mM HEPES. The prolongation of Ic, c. at pHo 8 could not be accounted for by a direct action on Ca 2+ channels, since tail currents were prolonged when pH o was changed rapidly during the tail current, after all Ca 2+ channels were closed. The effects of increasing pHo on Ic,~ c~, also could not be explained by a direct action on C1-channels, since changing to pH o 8 did not prolong Cl-tail currents when intracellular Ca 2+ concentration ([Ca2+] i) was fixed by EGTA in whole cell recordings. Raising pHo did, however, prolong depolarizationevoked [Ca2+] i transients, measured directly with the Ca 2+ indicator dye, fura-2. Taken together, these data demonstrate the presence of a Na+-independent, pHo-sensitive mechanism for reduction of [Ca2+]~ after influx through Ca 2+ channels. This mechanism is associated with the plasma membrane, and is active on a time scale that is relevant to the duration of single action potentials in these cells. We suggest that this mechanism is the plasma membrane Ca+ ATPase.