Nassar-Gentina V, Pollard H B, Rojas E
Laboratory of Cell Biology and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda 20892.
Am J Physiol. 1988 May;254(5 Pt 1):C675-83. doi: 10.1152/ajpcell.1988.254.5.C675.
Membrane potentials of medullary chromaffin cells of the adrenal gland of the mouse were measured in situ. Resting potential (-54.3 +/- 8.8 mV) depended on extracellular [K+] as predicted by the constant-field equation with a permeability ratio, PNa/PK, of 0.09. Current-voltage (I-V) relationships showed that the current is rectified across the chromaffin cell membrane. A rectification ratio of 0.4 was calculated from the slopes of the I-V curves for positive (41 +/- 26 M omega) and negative (103 +/- M omega) currents. Because input resistance for a resting chromaffin cell in isolation is approximately 5 G omega, the chromaffin cells in situ behave as if they were electrically coupled. Most cells responded to depolarizing current pulses with repetitive action potentials, but only 50% of them showed spontaneous electrical activity. Spontaneous activity was often seen in the presence of tetrodotoxin (3 microM). Although the application of the K+-channel blockers tetraethylammonium and Ba2+ greatly increased the amplitude of the action potentials, only Ba2+ induced continuous electrical activity. Application of acetylcholine (ACh) always depolarized the cell membrane. This effect was blocked by atropine but not by D-tubocurarine, suggesting that ACh stimulation of chromaffin cells in the mouse involves activation of muscarinic receptors.
对小鼠肾上腺髓质嗜铬细胞的膜电位进行了原位测量。静息电位（-54.3±8.8 mV）取决于细胞外[K⁺]，这与恒定场方程预测的结果一致，通透率比PNa/PK为0.09。电流-电压（I-V）关系表明，电流在嗜铬细胞膜上呈整流状态。根据I-V曲线的斜率计算出正电流（41±26 MΩ）和负电流（103±MΩ）的整流比为0.4。由于孤立的静息嗜铬细胞的输入电阻约为5 GΩ，因此原位嗜铬细胞的行为就好像它们是电耦合的。大多数细胞对去极化电流脉冲有重复动作电位反应，但只有50%的细胞表现出自发电活动。在存在河豚毒素（3 μM）的情况下经常能看到自发活动。虽然应用K⁺通道阻滞剂四乙铵和Ba²⁺大大增加了动作电位的幅度，但只有Ba²⁺能诱导持续电活动。应用乙酰胆碱（ACh）总是使细胞膜去极化。这种作用被阿托品阻断，但不被筒箭毒碱阻断，这表明小鼠嗜铬细胞的ACh刺激涉及毒蕈碱受体的激活。
