Morgado-Valle Consuelo, Beltran-Parrazal Luis, DiFranco Marino, Vergara Julio L, Feldman Jack L
Department of Neurobiology, David Geffen School of Medicine at UCLA, Box 951763, Los Angeles, CA 90095-1763, USA.
J Physiol. 2008 Sep 15;586(18):4531-40. doi: 10.1113/jphysiol.2008.154765. Epub 2008 Jul 17.
PreBötzinger Complex (preBötC) neurons are postulated to underlie respiratory rhythm generation. The inspiratory phase of the respiratory cycle in vitro results from preBötC neurons firing synchronous bursts of action potentials (APs) on top of 10-20 mV, 0.3-0.8 s inspiratory drive potentials. Is the inspiratory drive in individual neurons simply the result of the passive integration of inspiratory-modulated synaptic currents or do active processes modulate these currents? As somatic Ca(2+) is known to increase during inspiration, we hypothesized that it affects inspiratory drive. We combined whole cell recording in an in vitro slice preparation with Ca(2+) microfluorometry to detect single inspiratory neuron somatic Ca(2+) transients with high temporal resolution ( approximately mus). In neurons loaded with either Fluo-4 or Oregon Green BAPTA 5 N, we observed Ca(2+) transients associated with each AP. During inspiration, significant somatic Ca(2+) influx was a direct consequence of activation of voltage-gated Ca(2+) channels by APs. However, when we isolated the inspiratory drive potential in active preBötC neurons (by blocking APs with intracellular QX-314 or by hyperpolarization), we did not detect somatic Ca(2+) transients; yet, the parameters of inspiratory drive were the same with or without APs. We conclude that, in the absence of APs, somatic Ca(2+) transients do not shape the somatic inspiratory drive potential. This suggests that in preBötC neurons, substantial and widespread somatic Ca(2+) influx is a consequence of APs during the inspiratory phase and does not contribute substantively to the inspiratory drive potential. Given evidence that the Ca(2+) buffer BAPTA can significantly reduce inspiratory drive, we hypothesize that dendritic Ca(2+) transients amplify inspiratory-modulated synaptic currents.
前包钦格复合体（preBötC）神经元被认为是呼吸节律产生的基础。在体外，呼吸周期的吸气相是由preBötC神经元在10 - 20 mV、0.3 - 0.8 s的吸气驱动电位基础上发放同步动作电位（APs）爆发所致。单个神经元的吸气驱动仅仅是吸气调制突触电流被动整合的结果，还是有主动过程调节这些电流呢？由于已知在吸气过程中体细胞内Ca(2+)会增加，我们推测它会影响吸气驱动。我们将体外脑片制备中的全细胞记录与Ca(2+)显微荧光测定法相结合，以高时间分辨率（约毫秒级）检测单个吸气神经元的体细胞Ca(2+)瞬变。在加载了Fluo - 4或俄勒冈绿BAPTA 5 N的神经元中，我们观察到与每个AP相关的Ca(2+)瞬变。在吸气过程中，显著的体细胞Ca(2+)内流是APs激活电压门控Ca(2+)通道的直接结果。然而，当我们在活跃的preBötC神经元中分离出吸气驱动电位时（通过用细胞内QX - 314阻断APs或通过超极化），我们没有检测到体细胞Ca(2+)瞬变；然而，有无APs时吸气驱动的参数是相同的。我们得出结论，在没有APs的情况下，体细胞Ca(2+)瞬变不会塑造体细胞吸气驱动电位。这表明在preBötC神经元中，大量且广泛的体细胞Ca(2+)内流是吸气相期间APs的结果，并且对吸气驱动电位没有实质性贡献。鉴于有证据表明Ca(2+)缓冲剂BAPTA可显著降低吸气驱动，我们推测树突状Ca(2+)瞬变会放大吸气调制的突触电流。
