Catecholamine release from cat adrenal glands perfused at a high rate (4 ml min-1) at 37 degrees C with polarizing (1.2 or 5.9 mM K+) or depolarizing (17.7, 35, 59 or 118 mM K+) solutions, was triggered by 5 or 10 s pulses of Ca2+ (0.5 or 2.5 mM) in the presence of various concentrations of K+. 2. In polarized glands, secretion was greater the higher the K+ concentration present during the secretory K+/Ca2+ test pulse. Thus, in 17.7 mM K+, catecholamine released was 162 +/- 27 ng per pulse, while in 118 mM K+ secretion rose to 1839 +/- 98 ng per pulse. In depolarized glands, secretion reached a peak of around 1000 ng per pulse in 35-59 mM K+; in 118 mM K+, secretion did not increase further, suggesting that voltage changes are implicated in the control of the secretory process. 3. Blockade of secretion by increased concentrations of (+)-isradipine was much more manifest in polarized glands. The higher the degree of depolarization was (35, 59 or 118 mM K+), the lower the IC50 s were. So, the ratios between the IC50 s in polarized and depolarized glands rose from 3.92 in 35 mM K+ to 26.7 in 118 mM K+. 4. In contrast, the Ca2+ channel activator (-)-Bay K 8644 potentiated catecholamine release evoked by K+/Ca2+ pulses equally well in polarized or depolarized glands. The ratios between EC50 s in polarized or depolarized glands were, respectively, 0.30, 0.59 and 0.69 for 17.7, 35 and 118 mM K+. 5. In simultaneous experiments, the two enantiomers of Bay K 8644 exhibited opposite effects on secretion. (+)-Bay K 8644 (a Ca21 channel blocker) inhibited secretion better in depolarized than in polarized glands, whilst (-)-Bay K 8644 potentiated secretion in a voltage-independent manner. 6. Potentiation of secretion by (-)-Bay K 8644 was concentration-dependent from 10-8 to 10-6M. At 10- 5M, such potentiation largely disappeared in both polarized and depolarized glands. However, this dual effect of (-)Bay K 8644 was better seen in depolarizing conditions, suggesting that using the same enantiomer, the voltage-dependence is only seen when blockade of secretion dominates. 7. In the presence of increasing concentrations of (-)Bay K 8644 (3 x 10-9, 3 x 10-8 and 3 x 10-7M), the concentration-response curves for (+)isradipine to inhibit secretion were displaced to the right. However, a Schild plot of (dose ratio - 1) against (-)-Bay K 8644 concentrations gave a slope of 0.6, suggesting that the interactions between (+)-isradipine and (-)Bay K 8644 were non-competitive in nature. The pA2 for (-)-Bay K 8644 was 9.13. 8. Overall, the results suggest that potentiation of secretion by (-)Bay K 8644 (a voltage-independent phenomenon), and blockade by (+)-isradipine or (+-Bay K 8644 (a voltage-dependent phenomenon) might be exerted through binding of the dihydropyridines activators and blockers to separate sites on chromaffin cell L-type Ca2 + channels.
摘要
在37℃下，以4毫升/分钟的高速率用极化（1.2或5.9毫摩尔/升钾离子）或去极化（17.7、35、59或118毫摩尔/升钾离子）溶液灌注猫肾上腺，在不同浓度钾离子存在的情况下，通过5或10秒的钙离子（0.5或2.5毫摩尔/升）脉冲触发儿茶酚胺释放。2. 在极化腺体中，分泌性钾离子/钙离子测试脉冲期间存在的钾离子浓度越高，分泌量越大。因此，在17.7毫摩尔/升钾离子中，每个脉冲释放的儿茶酚胺为162±27纳克，而在118毫摩尔/升钾离子中，分泌量上升至每个脉冲1839±98纳克。在去极化腺体中，在35 - 59毫摩尔/升钾离子中分泌量达到约1000纳克/脉冲的峰值；在118毫摩尔/升钾离子中，分泌量不再增加，这表明电压变化与分泌过程的控制有关。3. （+）-异搏定浓度增加对分泌的阻断在极化腺体中表现得更为明显。去极化程度越高（35、59或118毫摩尔/升钾离子），半数抑制浓度（IC50）越低。因此，极化和去极化腺体中IC50的比值从35毫摩尔/升钾离子时的3.92上升至118毫摩尔/升钾离子时的26.7倍。4. 相比之下，钙离子通道激活剂（-）-Bay K 8644在极化或去极化腺体中对钾离子/钙离子脉冲诱发的儿茶酚胺释放增强作用相同。对于1十七点七、35和118毫摩尔/升钾离子，极化或去极化腺体中半数有效浓度（EC50）的比值分别为0.30、0.59和0.69。5. 在同步实验中，Bay K 8644的两种对映体对分泌表现出相反的作用。（+）-Bay K 8644（一种钙离子通道阻滞剂）在去极化腺体中比在极化腺体中对分泌的抑制作用更好，而（-）-Bay K 8644以电压非依赖性方式增强分泌。6. （-）-Bay K 8644对分泌的增强作用在10^-8至10^-6摩尔浓度范围内呈浓度依赖性。在10^-5摩尔时，这种增强作用在极化和去极化腺体中基本消失。然而，（-）-Bay K 8644的这种双重作用在去极化条件下更明显，这表明使用相同的对映体，只有当分泌阻断占主导时才会出现电压依赖性。7. 在（-）-Bay K 8644浓度增加（3×10^-9、3×10^-8和3×10^-7摩尔）的情况下，（+）-异搏定抑制分泌的浓度 - 反应曲线向右移动。然而，以（剂量比 - 1）对（-）-Bay K 8644浓度绘制的施尔德图斜率为0.6，这表明（+）-异搏定与（-）-Bay K 8644之间的相互作用本质上是非竞争性的。（-）-Bay K 8644的拮抗常数（pA2）为9.13。8. 总体而言，结果表明（-）-Bay K 8644对分泌的增强作用（一种电压非依赖性现象）以及（+）-异搏定或（±）-Bay K 8644对分泌的阻断作用（一种电压依赖性现象）可能是通过二氢吡啶激活剂和阻滞剂与嗜铬细胞L型钙离子通道上不同位点的结合来实现的。
