Ypey D L, Ravesloot J H, Buisman H P, Nijweide P J
Department of Physiology and Physiological Physics, Leiden, The Netherlands.
J Membr Biol. 1988;101(2):141-50. doi: 10.1007/BF01872829.
Patch-clamp measurements were made on osteoblast-like cells isolated from embryonic chick calvaria. Cell-attached-patch measurements revealed two types of high conductance (100-250 pS) channels, which rapidly activated upon 50-100 mV depolarization. One type showed sustained and the other transient activation over a 10-sec period of depolarization. The single-channel conductances of these channel types were about 100 or 250 pS, depending on whether the pipettes were filled with a low K+ (3 mM) or high K+ (143 mM) saline, respectively. The different reversal potentials under these conditions were consistent with at least K+ conduction. Whole-cell measurements revealed the existence of two types of outward rectifying conductances. The first type conducts K+ ions and activates within 20-200 msec (depending on the stimulus) upon depolarizing voltage steps from less than -60 mV to greater than -30 mV. It inactivates almost completely with a time constant of 2-3 sec. Recovery from inactivation is biphasic with an initial rapid phase (1-2 sec) followed by a slow phase (greater than 20 sec). The second whole-cell conductance activates at positive membrane potentials of greater than +50 mV. It also rapidly turns on upon depolarizing voltage steps. Activation may partly disappear at the higher voltages. Its single channels of 140 pS conductance were identified in the whole cell and did conduct K+ ions but were not highly Cl- or Na+ selective. The results show that osteoblasts may express various types of voltage controlled ionic channels. We predict a role for such channels in mineral metabolism of bone tissue and its control by osteoblasts.
对从胚胎小鸡颅骨分离出的成骨样细胞进行了膜片钳测量。细胞贴附式膜片测量揭示了两种高电导（100 - 250 pS）通道，它们在50 - 100 mV去极化时迅速激活。一种类型在10秒的去极化期间表现出持续激活，另一种则表现为瞬时激活。这些通道类型的单通道电导约为100或250 pS，这分别取决于微电极内填充的是低钾（3 mM）还是高钾（143 mM）盐溶液。在这些条件下不同的反转电位至少与钾离子传导一致。全细胞测量揭示了两种外向整流电导的存在。第一种传导钾离子，在从小于 - 60 mV去极化到大于 - 30 mV的电压阶跃时，在20 - 200毫秒内（取决于刺激）激活。它以2 - 3秒的时间常数几乎完全失活。从失活状态恢复是双相的，初始快速阶段（1 - 2秒）之后是缓慢阶段（大于20秒）。第二种全细胞电导在大于 + 50 mV的正膜电位时激活。它在去极化电压阶跃时也迅速开启。在较高电压下激活可能部分消失。在全细胞中鉴定出其单通道电导为140 pS，确实传导钾离子，但对氯离子或钠离子的选择性不高。结果表明，成骨细胞可能表达各种类型的电压控制离子通道。我们预测此类通道在骨组织的矿物质代谢及其由成骨细胞控制的过程中起作用。
