Campbell D T
Hatfield Marine Science Center, Oregon State University, Newport 97365-5296.
Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9569-73. doi: 10.1073/pnas.89.20.9569.
Sensory neurons of frog dorsal root ganglia (DRG) express at least two subtypes of voltage-gated Na channel and at least two subtypes of voltage-gated K channel. The Na channel subtypes have different sensitivities to tetrodotoxin (TTX) and different kinetics. The TTX-sensitive (TTX-s) Na channel inactivates rapidly and is blocked by nanomolar TTX. The TTX-insensitive (TTX-i) Na channel resists blockage by up to 100 microM TTX (it is blocked by saxitoxin) and inactivates 2-6 times more slowly. The two subtypes of voltage-gated K channel differ in activation kinetics: the fast subtype activates 2-8 times faster than the slow subtype. These Na and K channel subtypes are distributed differentially by cell size, falling into three major groups: (i) small cells with slowly activating K channels and a mixture of TTX-s and TTX-i Na channels; (ii) small cells with slowly activating K channels and TTX-s Na channels; and (iii) large cells with rapidly activating K channels and TTX-s Na channels. The contributions of these channel subtypes to the electrical properties of sensory neurons were investigated under conditions that minimized the contribution of Ca current. Under these conditions, action potential duration is correlated with the channel subtypes expressed: cells with both TTX-i and TTX-s Na channels and slowly activating K channels exhibit long-duration action potentials, cells with TTX-s Na channels and slowly activating K channels exhibit intermediate-duration action potentials, and cells with TTX-s Na channels and rapidly activating K channels exhibit short-duration action potentials.
青蛙背根神经节（DRG）的感觉神经元表达至少两种亚型的电压门控钠通道和至少两种亚型的电压门控钾通道。钠通道亚型对河豚毒素（TTX）具有不同的敏感性和不同的动力学特性。TTX敏感（TTX-s）钠通道快速失活，并被纳摩尔浓度的TTX阻断。TTX不敏感（TTX-i）钠通道能抵抗高达100微摩尔TTX的阻断（它被石房蛤毒素阻断），失活速度慢2至6倍。两种亚型的电压门控钾通道在激活动力学方面存在差异：快速激活亚型的激活速度比慢速激活亚型快2至8倍。这些钠通道和钾通道亚型根据细胞大小呈差异性分布，分为三大类：（i）具有慢速激活钾通道以及TTX-s和TTX-i钠通道混合物的小细胞；（ii）具有慢速激活钾通道和TTX-s钠通道的小细胞；（iii）具有快速激活钾通道和TTX-s钠通道的大细胞。在将钙电流的贡献降至最低的条件下，研究了这些通道亚型对感觉神经元电特性的影响。在这些条件下，动作电位持续时间与所表达的通道亚型相关：同时具有TTX-i和TTX-s钠通道以及慢速激活钾通道的细胞表现出长时程动作电位，具有TTX-s钠通道和慢速激活钾通道的细胞表现出中等时程动作电位，而具有TTX-s钠通道和快速激活钾通道的细胞表现出短时程动作电位。
