Institute of Neuroscience and Brain Research Center, National Yang-Ming University, 155, Section 2, Li-Nong Street, Taipei 112, Taiwan, Republic of China.
Neuroscience. 2009 Dec 29;164(4):1701-11. doi: 10.1016/j.neuroscience.2009.09.052. Epub 2009 Sep 25.
Calcium is known to regulate several phenomena like neuronal excitability and plasticity. Interestingly, the spatiotemporal profile of dendritic calcium depends on several processes, specific to each neuronal type. In this study, we investigated Ca(2+) buffering and action potential (AP)-evoked Ca(2+) signaling in the dendrites of anatomically identified oriens lacunosum-moleculare (O-LM) cells, a major type of dendrite-targeting interneurons in the hippocampal CA1 region, using a combination of whole-cell patch-clamp recording and fast Ca(2+) imaging in acute rat brain slices. Cells were loaded with fluorescent Ca(2+) indicators fura-2 or Oregon Green BAPTA-1 (OGB-1) via patch-clamping electrode, and the effect of fura-2 on AP-evoked dendritic Ca(2+) transients was determined by ratiometric Ca(2+) imaging. To estimate intracellular Ca(2+) concentrations (Ca(2+)) and endogenous Ca(2+)-binding ratio (kappa(s)) in the proximal dendrite, fluorescence signals were converted into Ca(2+) using the ratioing method and were analyzed on the basis of the "single compartment model." Resting Ca(2+) was 22+/-5 nM and the build-up of Ca(2+) during a single AP was up to 656+/-226 nM. Analysis of Ca(2+) transients revealed that O-LM cells have a relatively low endogenous Ca(2+)-binding ratio (kappa(s)): the kappa(s) was 20+/-8 estimated during fura-2 loading and 27 estimated under steady-state fura-2 concentrations, respectively. To further examine the spatial profile of dendritic Ca(2+) transients, we measured somatic AP-evoked Ca(2+) transients beyond proximal dendrites using OGB-1. Dendritic Ca(2+) transients evoked by single APs or AP trains are not limited to regions close to the soma. The amplitude and decay of Ca(2+) associated with backpropagating APs are relatively independent of the distance from the soma. In sum, O-LM cells exhibit low endogenous Ca(2+)-binding ratios and relatively distance-independent Ca(2+) dynamics in the dendrites. These special features of Ca(2+) signaling in O-LM cells may have important functional implications for both normal and pathological conditions.
钙已知调节几种现象，如神经元兴奋性和可塑性。有趣的是，树突钙的时空分布取决于特定于每种神经元类型的几个过程。在这项研究中，我们使用急性大鼠脑片的全细胞膜片钳记录和快速钙成像相结合，研究了在解剖学上确定的或门腔隙分子（O-LM）细胞的树突中的钙缓冲和动作电位（AP）诱发的钙信号，O-LM 细胞是海马 CA1 区中主要的树突靶向中间神经元类型。通过膜片钳电极将荧光钙指示剂 fura-2 或 Oregon Green BAPTA-1（OGB-1）加载到细胞中，并通过比率钙成像确定 fura-2 对 AP 诱发的树突钙瞬变的影响。为了估计近侧树突中的细胞内钙浓度([Ca2+]i)和内源性钙结合比（kappa(s)），使用比率法将荧光信号转换为[Ca2+]i，并根据“单室模型”进行分析。静息[Ca2+]i为 22+/-5 nM，单个 AP 期间[Ca2+]i 的增加高达 656+/-226 nM。钙瞬变分析表明，O-LM 细胞具有相对较低的内源性钙结合比（kappa(s)）：在 fura-2 加载期间分别估计 kappa(s)为 20+/-8，在稳态 fura-2 浓度下估计 kappa(s)为 27。为了进一步研究树突钙瞬变的空间分布，我们使用 OGB-1 测量了远侧近侧树突的体 AP 诱发钙瞬变。单个 AP 或 AP 串诱发的树突钙瞬变不仅限于靠近体的区域。与逆行 AP 相关的[Ca2+]i 的幅度和衰减与距体的距离相对独立。总之，O-LM 细胞在树突中表现出低内源性钙结合比和相对距离独立的钙动力学。O-LM 细胞中钙信号的这些特殊特征可能对正常和病理条件都具有重要的功能意义。
