Sugawara Y
Department of Physiology, Teikyo University School of Medicine, Tokyo, Japan.
J Gen Physiol. 1989 Feb;93(2):365-80. doi: 10.1085/jgp.93.2.365.
In the isolated sensory epithelium of the Plotosus electroreceptor, the receptor current has been dissected into inward Ca current, ICa, and superimposed outward transient of Ca-gated K current, IK(Ca). In control saline (170 mM/liter Na), with IK(Ca) abolished by K blockers, ICa declined in two successive exponential phases with voltage-dependent time constants. Double-pulse experiments revealed that the test ICa was partially depressed by prepulses, maximally near voltage levels for the control ICa maximum, which suggests current-dependent inactivation. In low Na saline (80 mM/liter), ICa declined in a single phase with time constants similar to those of the slower phase in control saline. The test ICa was then unaffected by prepulses. The implied presence of two Ca current components, the fast and slow ICa's, were further examined. In control saline, the PSP externally recorded from the afferent nerve showed a fast peak and a slow tonic phase. The double-pulse experiments revealed that IK(Ca) and the peak PSP were similarly depressed, i.e., secondarily to inactivation of the peak current. The steady inward current, however, was unaffected by prolonged prepulses that were stepped to 0 mV, the in situ DC level. Therefore, the fast ICa seems to initiate IK(Ca) and phasic release of transmitter, which serves for phasic receptor responses. The slow ICa may provide persistent active current, which has been shown to maintain tonic receptor operation.
在豹鲂鮄电感受器的分离感觉上皮中，受体电流已被分解为内向钙电流（ICa）和叠加的钙门控钾电流外向瞬变（IK(Ca)）。在对照盐溶液（170 mM/升钠）中，当IK(Ca)被钾阻滞剂消除时，ICa在两个连续的指数阶段下降，具有电压依赖性时间常数。双脉冲实验表明，测试ICa被预脉冲部分抑制，在对照ICa最大值的电压水平附近抑制最大，这表明存在电流依赖性失活。在低钠盐溶液（80 mM/升）中，ICa在单相中下降，时间常数与对照盐溶液中较慢阶段的相似。此时测试ICa不受预脉冲影响。对隐含的两种钙电流成分，即快速和慢速ICa，进行了进一步研究。在对照盐溶液中，从传入神经外部记录的PSP显示出一个快速峰值和一个缓慢的强直期。双脉冲实验表明，IK(Ca)和PSP峰值同样受到抑制，即继发于峰值电流的失活。然而，稳定的内向电流不受步进到0 mV（原位直流水平）的长时间预脉冲的影响。因此，快速ICa似乎启动了IK(Ca)和递质的相位释放，这用于相位受体反应。慢速ICa可能提供持续的激活电流，已证明其可维持紧张性受体活动。
