PRESSURE-DEPENDENCE OF SODIUM GATING CURRENTS IN THE SQUID GIANT-AXON
PRESSURE-DEPENDENCE OF SODIUM GATING CURRENTS IN THE SQUID GIANT-AXON
复制标题
DOI：
10.1007/bf00276629
复制
发表时间：
1984-01-01
影响因子：
2
通讯作者：
STUHMER, W
中科院分区：
文献类型：
--
作者：
CONTI, F;INOUE, I;STUHMER, W
在不同静水压力P（最高达60兆帕斯卡）下，测量了鱿鱼轴突中的不对称位移电流Ig。胞内Cs+和TEA+[四乙基铵]能消除K和Na电流，但胞外河豚毒素（TTX）和Tris+取代Na+能消除K和Na电流。Ig的时间过程随着压力的增加逐渐变慢，振幅减小。在适当的时间和振幅尺度下，任何给定P点的Ig记录都可以与大气压下的Ig记录很好地叠加。相同的比例因子产生了在-30至+42 mV范围内从电压阶跃到膜电位的所有记录的良好叠加。振幅因子与时间因子之比大于1，且随P增大而增大，表明总电荷位移Q逐渐减小（在60 MPa时可达35%），但其电压依赖性无显著变化。时间标度因子随P呈指数增长，如果涉及Na通道打开和产生主要电荷再分配的所有步骤具有相同的激活体积，则可以预期。17个立方厘米/摩尔。这个值大约是表征Na电流激活的压力依赖性的1/2，这表明在Na通道打开的某个后期限速步骤中，有很大的激活体积，而没有伴随容易检测到的电荷运动。Q随压力降低的部分原因可能是Na失活的增加。然而，不能排除快速激活Na通道数量可逆减少的可能性，类似于已报道的在低温下发生的现象。
Asymmetric displacement currents, Ig, were measured in squid axons at different hydrostatic pressures, P, up to 60 MPa [megapascals]. K and Na currents were abolished by intracellular Cs+ and TEA+ [tetraethylammonium], but extracellular tetrodotoxin (TTX), and by Na+ substitution with Tris+. The time course of Ig became progressively slower with increasing pressure, and the amplitude decreased. With appropriate scaling in time and amplitude, Ig records at any given P could be made to superimpose very well with those obtained at atmospheric pressure. The same scaling factors yielded a good superposition of all records obtained for voltage steps to membrane potentials in the range -30 to +42 mV. The ratio between the amplitude and time factors was larger than unity and increased with P, indicating a progressive decrease (up to 35% at 60 MPa) of the total charge displaced, Q, with no significant change in its voltage dependence. The time-scaling factor increased exponentially with P, as expected if all the steps involved in the opening of a Na channel, and producing a major charge redistribution, have the same activation volume, .apprx. 17 cm3/mol. This value is roughly 1/2 of that characterizing the pressure dependence of Na current activation, suggesting that some late, rate-limiting step in the opening of Na channels has a large activation volume without being accompanied by an easily detected charge movement. Part of the decrease of Q with pressure could be attributed to an increase in Na inactivation. However, the possibility that there is a reversible reduction in the number of fast activating Na channels, similar to the phenomenon that has been reported to occur at low temperatures cannot be excluded.