Del Negro Christopher A, Koshiya Naohiro, Butera Robert J, Smith Jeffrey C
Cellular and Systems Neurobiology Section, Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4455, USA.
J Neurophysiol. 2002 Nov;88(5):2242-50. doi: 10.1152/jn.00081.2002.
We measured persistent Na(+) current and membrane properties of bursting-pacemaker and nonbursting inspiratory neurons of the neonatal rat pre-Bötzinger complex (pre-BötC) in brain stem slice preparations with a rhythmically active respiratory network in vitro. In whole-cell recordings, slow voltage ramps (</=100 mV/s) inactivated the fast, spike-generating Na(+) current and yielded N-shaped current-voltage relationships with nonmonotonic, negative-slope regions between -60 and -35 mV when the voltage-sensitive component was isolated. The underlying current was a TTX-sensitive persistent Na(+) current (I(NaP)) since the inward current was present at slow voltage ramp speeds (3.3-100 mV/s) and the current was blocked by 1 microM TTX. We measured the biophysical properties of I(NaP) after subtracting the voltage-insensitive "leak" current (I(Leak)) in the presence of Cd(2+) and in some cases tetraethylammonium (TEA). Peak I(NaP) ranged from -50 to -200 pA at a membrane potential of -30 mV. Decreasing the speed of the voltage ramp caused time-dependent I(NaP) inactivation, but this current was present at ramp speeds as low as 3.3 mV/s. I(NaP) activated at -60 mV and obtained half-maximal activation near -40 mV. The subthreshold voltage dependence and slow inactivation kinetics of I(NaP), which closely resemble those of I(NaP) mathematically modeled as a burst-generation mechanism in pacemaker neurons of the pre-BötC, suggest that I(NaP) predominantly influences bursting dynamics of pre-BötC inspiratory pacemaker neurons in vitro. We also found that the ratio of persistent Na(+) conductance to leak conductance (g(NaP)/g(Leak)) can distinguish the phenotypic subpopulations of bursting pacemaker and nonbursting inspiratory neurons: pacemaker neurons showed g(NaP)/g(Leak) > g(NaP)/g(Leak) in nonpacemaker cells (P < 0.0002). We conclude that I(NaP) is ubiquitously expressed by pre-BötC inspiratory neurons and that bursting pacemaker behavior within the heterogeneous population of inspiratory neurons is achieved with specific ratios of these two conductances, g(NaP) and g(Leak).
我们在具有体外节律性活跃呼吸网络的脑干切片标本中，测量了新生大鼠前包钦格复合体（pre - BötC）中爆发式起搏和非爆发式吸气神经元的持续性钠电流及膜特性。在全细胞记录中，缓慢电压斜坡（≤100 mV/s）使快速的、产生动作电位的钠电流失活，当分离出电压敏感成分时，产生了N形电流 - 电压关系，在 - 60至 - 35 mV之间有非单调的负斜率区域。潜在电流是一种对河豚毒素（TTX）敏感的持续性钠电流（I(NaP)），因为内向电流在缓慢电压斜坡速度（3.3 - 100 mV/s）时存在，且该电流被1 μM TTX阻断。在存在镉离子（Cd(2+)）以及某些情况下四乙铵（TEA）时，减去电压不敏感的“漏”电流（I(Leak)）后，我们测量了I(NaP)的生物物理特性。在 - 30 mV膜电位时，I(NaP)峰值范围为 - 50至 - 200 pA。降低电压斜坡速度会导致I(NaP)出现时间依赖性失活，但在低至3.3 mV/s的斜坡速度时该电流仍存在。I(NaP)在 - 60 mV时激活，在 - 40 mV附近达到半最大激活。I(NaP)的阈下电压依赖性和缓慢失活动力学，在数学上与作为pre - BötC起搏神经元爆发产生机制建模的I(NaP)非常相似，这表明I(NaP)在体外主要影响pre - BötC吸气起搏神经元的爆发动力学。我们还发现，持续性钠电导与漏电导的比值（g(NaP)/g(Leak)）可以区分爆发式起搏和非爆发式吸气神经元的表型亚群：起搏神经元的g(NaP)/g(Leak)大于非起搏细胞中的g(NaP)/g(Leak)（P < 0.0002）。我们得出结论，I(NaP)在前包钦格复合体吸气神经元中普遍表达，并且吸气神经元异质群体中的爆发式起搏行为是通过这两种电导g(NaP)和g(Leak)的特定比值实现的。
