CONTRIBUTION OF 2 TYPES OF CALCIUM CURRENTS TO THE PACEMAKER POTENTIALS OF RABBIT SINO-ATRIAL NODE CELLS
CONTRIBUTION OF 2 TYPES OF CALCIUM CURRENTS TO THE PACEMAKER POTENTIALS OF RABBIT SINO-ATRIAL NODE CELLS
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DOI：
10.1113/jphysiol.1988.sp016916
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发表时间：
1988-01-01
影响因子：
5.5
通讯作者：
KAMEYAMA, M
中科院分区：
文献类型：
--
作者：
HAGIWARA, N;IRISAWA, H;KAMEYAMA, M
1.用全细胞膜片钳和细胞贴附式膜片钳技术在家兔单个窦房结细胞上记录了瞬时型和长时型两种钙电流。2.在全细胞箝位模式中，响应于从-80 mV的保持电位到-40 mV的去极化脉冲，产生幅度为2.1 ± 2.5 mV的瞬时型钙电流。0.7 pA/pF（平均值±. S.D.; n = 15）。阈值电位约为-50 mV。3.镍（40 μ M）和胺菊酯（0.1 μ M）阻断瞬时型钙电流，而对持久型没有明显影响。硝苯地平和D 600阻断持久型，但不影响短暂型。镉（20 μ M）和钴（2 mM）同等地抑制两种类型的钙电流。4.这两种类型的钙电流的幅度随着细胞外钙离子浓度的增加而增加。米氏常数Km的值为0.95 mM的瞬时型和3.92 mM的持久型，表明这些类型代表两种不同类型的通道。5.在细胞贴附式膜片钳模式下，瞬时型钙电流的单通道电导为8.5pS，而长时型钙电流的单通道电导为16.0pS。这些值中的每一个分别与其他细胞中发现的值相似。6.在全细胞钳模式下，瞬时型电流在-70 mV时开始失活，在-40 mV时完全失活。瞬时型电流的稳态失活曲线比持久型电流负50 mV左右。活化和失活曲线之间的膜电位重叠很小。随着电位在-80 ~+30 mV范围内逐渐变为正值，失活时间常数从20 ms缩短至5 ms。7.异丙肾上腺素（1 μ M）增加了长时型钙电流的幅度，但对瞬时型无效，表明长时型钙电流可能是异丙肾上腺素的正性变时作用的原因。8.当记录细胞的自发电活动时，施加40 μ M-镍诱导心动过缓，并且当膜持续超极化时，该效应增强。心动过缓主要是由起搏器去极化后期的去极化率降低引起的。镍引起的心动过缓既不是由于阻断超极化激活的内向电流，也不是由于抑制延迟整流钾电流。9.结果表明，心肌结细胞中存在瞬时型钙通道，该通道参与了舒张期慢去极化的后半期。
1. Two types of calcium currents, the transient type and long-lasting type, were examined by both whole-cell and cell-attached patch-clamp modes in single isolated sino-atrial node cells of the rabbit. 2. In the whole-cell clamp mode, in response to a depolarizing pulse to -40 mV from a holding potential of -80 mV, a transient type calcium current with an amplitude of 2.1 .+-. 0.7 pA/pF (mean .+-. S.D.; n = 15) was recorded. The threshold potential was approximately -50 mV. 3. Nickel (40 .mu.M) and tetramethrin (0.1 .mu.M) blocked the transient type calcium current without appreciable effects on the long-lasting type. Nifedipine and D600 blocked the long-lasting type, but did not affect the transient type. Cadmium (20 .mu.M) and cobalt (2 mM) inhibited both types of calcium currents equally. 4. Both types of calcium currents showed an increased amplitude with increasing extracellular calcium concentration. The values of the Michaelis constant, Km, were 0.95 mM for the transient type and 3.92 mM for the long-lasting type, indicating that these types represent two different classes of channels. 5. In the cell-attached patch-clamp mode, the single-channel conductance of the transient type calcium current was 8.5 pS, by using 100 mM-BaCl2 in the pipette, whereas that of the long-lasting type was 16.0 pS, under the same conditions. Each of these values was similar to those found in other cells, respectively. 6. In the whole-cell clamp mode, the transient type current began to inactivate at -70 mV and was full inactivated at -40 mV. The steady-state inactivation curve of the transient type current was approximately 50 mV negative to that of the long-lasting type. The overlap of the membrane potential between the activation and inactivation curves was small. The time constant of the inactivation shortened from 20 to 5 ms as the potential became progressively positive over the range from -80 to +30 mV. 7. Isoprenaline (1 .mu.M) increased the amplitude of the long-lasting type Ca2+ current, but was not effective on the transient type, suggesting that the long-lasting type calcium current may be responsible for the positive chronotropic effect of isoprenaline. 8. While recording spontaneous electrical activity of the cell, application of 40 .mu.M-nickel induced bradycardia and this effect was enhanced when the membrane was constantly hyperpolarized. The bradycardia was caused mainly by a reduction in the rate of depolarization in the later phase of the pacemaker depolarization. The bradycardia elicited by nickel was due neither to blockade of the hyperpolarization-activated inward current nor to inhibition of the delayed rectifier potassium current. 9. It was concluded that the transient type calcium channel exists in the cardiac nodal cell and that the current participates in the later half of the slow diastolic depolarization.