Voltage-gated transient currents in bovine adrenal fasciculata cells. I. T-type Ca2+ current.
Voltage-gated transient currents in bovine adrenal fasciculata cells. I. T-type Ca2+ current.
复制标题
牛肾上腺筋膜细胞中电压门控瞬时电流。 I. T型Ca2+电流。
DOI：
10.1085/jgp.102.2.217
复制
发表时间：
1993-08
影响因子：
3.8
通讯作者：
Enyeart, J J
中科院分区：
文献类型：
--
作者：
Mlinar, B;Biagi, B A;Enyeart, J J
全细胞版膜片钳技术用于鉴定和表征酶解牛肾上腺束状带（AZF）细胞中的电压门控Ca2+通道。绝大多数细胞（86个中的84个）仅表达低电压激活，快速失活Ca2+电流，具有其他细胞中描述的t型Ca2+电流的特性。该电流的电压依赖性激活通过波尔兹曼函数拟合到整数幂为4，中点为-17 mV。从激活曲线和使用“极限对数电位灵敏度”获得的单通道门控电荷的独立估计分别为8.1和6.8个基本电荷。失活是电压的陡函数，v1/2为-49.9 mV，斜率因子K为3.73 mV。通过AZF细胞表达单一Ca2+通道亚型，可以在广泛的电位范围内研究电压依赖性门控和T电流的动力学特性。对Ca2+电流门控动力学的分析表明，T通道的激活、失活、失活（关闭）和再激活（从失活中恢复）都包括在极端电压下成为速率限制的电压无关跃迁。Ca2+电流激活电压依赖的s型动力学描述了一个m4模型。激活时间常数在-30和+10 mV之间呈指数变化，接近与电压无关的最小值1.6 ms。在电位正至0 mV时，失活时间常数（tau i）也呈指数下降至最小值18.3 ms。负电压越大，T通道闭合（失活）速度越快；在-40 ~ -150 mV电位范围内，失活时间常数（tau d）从8.14 +/- 0.7 ms降至0.48 +/- 0.1 ms。被去极化灭活的T通道沿着包括两个电压相关时间常数的通路返回到闭合状态。当恢复电位在- 50 ~ -90 mV范围内变化时，tau recs的变化范围为8.11 ~ 4.80 s， tau recs的变化范围为1.01 ~ 0.372 s。电位负至-70 mV时，两个时间常数均接近最小值。T通道选择性拮抗剂Ni2+阻断AZF细胞中低压激活的Ca2+电流，IC50为20微米。在相同浓度下，Ni2+还能阻断促肾上腺皮质激素刺激的皮质醇分泌。我们的研究结果表明，牛AZF细胞在主要或完全表达t型Ca2+通道的分泌细胞中是独特的。（摘要删节为400字）
The whole cell version of the patch clamp technique was used to identify and characterize voltage-gated Ca2+ channels in enzymatically dissociated bovine adrenal zona fasciculata (AZF) cells. The great majority of cells (84 of 86) expressed only low voltage-activated, rapidly inactivating Ca2+ current with properties of T-type Ca2+ current described in other cells. Voltage-dependent activation of this current was fit by a Boltzmann function raised to an integer power of 4 with a midpoint at -17 mV. Independent estimates of the single channel gating charge obtained from the activation curve and using the "limiting logarithmic potential sensitivity" were 8.1 and 6.8 elementary charges, respectively. Inactivation was a steep function of voltage with a v1/2 of -49.9 mV and a slope factor K of 3.73 mV. The expression of a single Ca2+ channel subtype by AZF cells allowed the voltage-dependent gating and kinetic properties of T current to be studied over a wide range of potentials. Analysis of the gating kinetics of this Ca2+ current indicate that T channel activation, inactivation, deactivation (closing), and reactivation (recovery from inactivation) each include voltage-independent transitions that become rate limiting at extreme voltages. Ca2+ current activated with voltage- dependent sigmoidal kinetics that were described by an m4 model. The activation time constant varied exponentially at test potentials between -30 and +10 mV, approaching a voltage-independent minimum of 1.6 ms. The inactivation time constant (tau i) also decreased exponentially to a minimum of 18.3 ms at potentials positive to 0 mV. T channel closing (deactivation) was faster at more negative voltages; the deactivation time constant (tau d) decreased from 8.14 +/- 0.7 to 0.48 +/- 0.1 ms at potentials between -40 and -150 mV. T channels inactivated by depolarization returned to the closed state along pathways that included two voltage-dependent time constants. tau rec-s ranged from 8.11 to 4.80 s when the recovery potential was varied from - 50 to -90 mV, while tau rec-f decreased from 1.01 to 0.372 s. At potentials negative to -70 mV, both time constants approached minimum values. The low voltage-activated Ca2+ current in AZF cells was blocked by the T channel selective antagonist Ni2+ with an IC50 of 20 microM. At similar concentrations, Ni2+ also blocked cortisol secretion stimulated by adrenocorticotropic hormone. Our results indicate that bovine AZF cells are distinctive among secretory cells in expressing primarily or exclusively T-type Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)