Ceña V, Rojas E
Laboratory of Cell Biology and Genetics, NIDDK, National Institutes of Health, Bethesda, MD 20892.
Biochim Biophys Acta. 1990 Apr 13;1023(2):213-22. doi: 10.1016/0005-2736(90)90416-l.
Adrenal chromaffin cells secrete catecholamines (CA) and ATP in response to acetylcholine (ACh) and high [K+]o. The release process is relatively fast making it difficult to measure the early phase of the secretory response. Recently we were able to resolve the time course of the secretory response by measuring the release of ATP using luciferin-luciferase included in the extracellular medium. For the three secretagogues studied, ACh, nicotine and high [K+]o, the early phase of release followed a complex kinetics. Allowing for an initial delay of the secretory response, the kinetics could be described as the sum of two power exponential processes. Increasing the temperature from 23 to 37 degrees C induced a marked decrease in the two time constants needed to fit the early time course of the ATP secretion. The activation energies, estimated from Arrhenius plots, were approx. 20 and 16 kcal/mol for both phases of ATP release induced by either cholinergic agonists or high [K+]o. These results suggest that cholinergic receptor activation and membrane depolarization induce ATP (and CA) secretion through a common pathway. The initial delay in the onset of the secretory response decreased with increasing doses of secretagogue and with temperature. We propose that the delay preceding the actual onset of ATP release represents the time required for generation of intracellular second messengers. The effective concentration attained by these messengers depend apparently on both receptor occupancy by the agonist and the ensuing Ca2+ channel activation.
肾上腺嗜铬细胞在乙酰胆碱（ACh）和高细胞外钾离子浓度（[K⁺]o）作用下分泌儿茶酚胺（CA）和三磷酸腺苷（ATP）。释放过程相对较快，使得测量分泌反应的早期阶段变得困难。最近，我们通过测量细胞外培养基中包含的荧光素 - 荧光素酶来测定ATP的释放，从而解析了分泌反应的时间进程。对于所研究的三种促分泌剂，即ACh、尼古丁和高[K⁺]o，释放的早期阶段遵循复杂的动力学。考虑到分泌反应的初始延迟，动力学可以描述为两个幂指数过程的总和。将温度从23℃升高到37℃导致拟合ATP分泌早期时间进程所需的两个时间常数显著降低。根据阿伦尼乌斯曲线估计，由胆碱能激动剂或高[K⁺]o诱导的ATP释放的两个阶段的活化能约为20和16千卡/摩尔。这些结果表明，胆碱能受体激活和膜去极化通过共同途径诱导ATP（和CA）分泌。分泌反应开始时的初始延迟随着促分泌剂剂量的增加和温度的升高而减少。我们提出，在ATP实际释放之前的延迟代表产生细胞内第二信使所需的时间。这些信使达到的有效浓度显然取决于激动剂对受体的占据情况以及随之而来的钙通道激活。
