Heflin Stephanie J, Cook Paul B
Program in Neuroscience, Boston University, Boston, Massachusetts 02214, USA.
Vis Neurosci. 2007 Mar-Apr;24(2):197-206. doi: 10.1017/S095252380707040X.
Action potentials in amacrine cells are important for lateral propagation of signals across the inner retina, but it is unclear how many subclasses of amacrine cells contain voltage-gated sodium channels or can fire action potentials. This study investigated the ability of amacrine cells with narrow ( <200 microm) and wide (>200 microm) dendritic fields to fire action potentials in response to depolarizing current injections and light stimulation. The pattern of action potentials evoked by current injections revealed two distinct classes of amacrine cells; those that responded with a single action potential (single-spiking cells) and those that responded with repetitive action potentials (repetitive-spiking cells). Repetitive-spiking cells differed from single-spiking cells in several regards: Repetitive-spiking cells were more often wide field cells, while single-spiking cells were more often narrow field cells. Repetitive-spiking cells had larger action potential amplitudes, larger peak voltage-gated NaV currents lower action potential thresholds, and needed less current to induce action potentials. However, there was no difference in the input resistance, holding current or time constant of these two classes of cells. The intrinsic capacity to fire action potentials was mirrored in responses to light stimulation; single-spiking amacrine cells infrequently fired action potentials to light steps, while repetitive-spiking amacrine cells frequently fired numerous action potentials. These results indicate that there are two physiologically distinct classes of amacrine cells based on the intrinsic capacity to fire action potentials.
无长突细胞中的动作电位对于信号在视网膜内层的横向传播很重要，但尚不清楚无长突细胞的多少亚类含有电压门控钠通道或能够产生动作电位。本研究调查了树突野窄（<200微米）和宽（>200微米）的无长突细胞在去极化电流注入和光刺激下产生动作电位的能力。电流注入诱发的动作电位模式揭示了两类不同的无长突细胞；一类以单个动作电位做出反应（单峰细胞），另一类以重复动作电位做出反应（重复峰细胞）。重复峰细胞在几个方面与单峰细胞不同：重复峰细胞更常是宽野细胞，而单峰细胞更常是窄野细胞。重复峰细胞具有更大的动作电位幅度、更大的峰值电压门控NaV电流、更低的动作电位阈值，并且诱导动作电位所需的电流更少。然而，这两类细胞的输入电阻、钳制电流或时间常数没有差异。产生动作电位的内在能力在对光刺激的反应中也有体现；单峰无长突细胞对光阶跃很少产生动作电位，而重复峰无长突细胞经常产生大量动作电位。这些结果表明，基于产生动作电位的内在能力，存在两类生理上不同的无长突细胞。
