Gerber S H, Haunstetter A, Krüger C, Kaufmann A, Nobiling R, Haass M
Department of Cardiology, University of Heidelberg, Germany.
Am J Physiol. 1995 Sep;269(3 Pt 1):C572-81. doi: 10.1152/ajpcell.1995.269.3.C572.
Intracellular free sodium ([Na+]i) and calcium ([Ca2+]i) concentrations were determined by sodium-binding benzofuran isophthalate (SBFI) and fura 2 microfluorimetry, respectively, in bovine adrenal chromaffin cells (BCC). Validation of SBFI microfluorimetry by in vitro and in vivo calibration revealed a reliable assessment of [Na+]i within a range of 1-30 mM in single BCC. Nicotine (0.1-10 microM) induced concentration-dependent increases of both [Na+]i (from 3.3 +/- 0.1 to 25.6 +/- 0.4 mM, n = 76, P < 0.001) and [Ca2+]i (from 64 +/- 1 to 467 +/- 16 nM, n = 87, P < 0.001), which were accompanied by an increase in [3H]norepinephrine (NE) release. Consistent with an exocytotic release mechanism, nicotine-induced increments of [Ca2+]i and [3H]NE release were reduced under calcium-free conditions and by gadolinium chloride (40 microM), whereas [Na+]i was not affected. In contrast, a parallel attenuation of nicotine-evoked changes in [Na+]i, [Ca2+]i, and [3H]NE release was observed during reduction of the extracellular sodium concentration. The nicotine-evoked responses were neutralized by the nicotinic receptor antagonist hexamethonium (100 microM) but not by blockade of voltage-dependent sodium channels (1 microM tetrodotoxin). In conclusion, the nicotine-induced exocytotic release of [3H]NE is triggered by an increase in [Ca2+]i, which is facilitated by sodium influx through the nicotinic receptor ionophore.
分别采用钠结合苯并呋喃异酞酸酯（SBFI）和fura 2显微荧光测定法，测定牛肾上腺嗜铬细胞（BCC）内的细胞内游离钠（[Na⁺]i）和钙（[Ca²⁺]i）浓度。通过体外和体内校准对SBFI显微荧光测定法进行验证，结果显示在单个BCC中，在1 - 30 mM范围内可可靠评估[Na⁺]i。尼古丁（0.1 - 10 μM）引起[Na⁺]i（从3.3±0.1 mM增至25.6±0.4 mM，n = 76，P < 0.001）和[Ca²⁺]i（从64±1 nM增至467±16 nM，n = 87，P < 0.001）浓度依赖性增加，同时伴有[³H]去甲肾上腺素（NE）释放增加。与胞吐释放机制一致，在无钙条件下以及用氯化钆（40 μM）处理时，尼古丁诱导的[Ca²⁺]i增加和[³H]NE释放减少，而[Na⁺]i不受影响。相反，在降低细胞外钠浓度期间，观察到尼古丁引起的[Na⁺]i、[Ca²⁺]i和[³H]NE释放变化同时减弱。尼古丁引起的反应被烟碱受体拮抗剂六甲铵（100 μM）中和，但不受电压依赖性钠通道阻断剂（1 μM河豚毒素）的影响。总之，尼古丁诱导的[³H]NE胞吐释放是由[Ca²⁺]i增加触发的，而钠通过烟碱受体离子通道内流促进了这一过程。
