Wu Y N, Wagner P D
Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Biochim Biophys Acta. 1991 May 17;1092(3):384-90. doi: 10.1016/s0167-4889(97)90016-1.
A protein phosphatase and phosphatase inhibitors were used to examine the role of protein phosphorylation in the regulation of norepinephrine secretion in digitonin-permeabilized bovine chromaffin cells. Addition of okadaic acid, a potent inhibitor of type 1 and type 2A protein phosphatases, or 1-naphthylphosphate, a more general phosphatase inhibitor, to digitonin-permeabilized chromaffin cells caused about a 100% increase in the amount of norepinephrine secreted in the absence of Ca2+ (in 5 mM EGTA) without affecting the amount of norepinephrine secreted in the presence of 10 microM free Ca2+. This stimulation of norepinephrine secretion by protein phosphatase inhibitors suggests that in the absence of Ca2+ there is a slow rate phosphorylation and that this phosphorylation triggers secretion. Addition of an exogenous type 2A protein phosphatase caused almost a 50% decrease in Ca(2+)-dependent norepinephrine secretion. Thus, the amounts of norepinephrine released both in the absence of Ca2+ and in the presence of Ca2+ appear to depend upon the level of protein phosphorylation.
使用一种蛋白磷酸酶和磷酸酶抑制剂来研究蛋白磷酸化在洋地黄皂苷通透的牛嗜铬细胞去甲肾上腺素分泌调节中的作用。向洋地黄皂苷通透的嗜铬细胞中添加冈田酸（一种1型和2A型蛋白磷酸酶的强效抑制剂）或1-萘基磷酸酯（一种更通用的磷酸酶抑制剂），在无Ca2+（在5 mM乙二醇双四乙酸中）的情况下，去甲肾上腺素分泌量增加了约100%，而不影响在存在10 microM游离Ca2+时去甲肾上腺素的分泌量。蛋白磷酸酶抑制剂对去甲肾上腺素分泌的这种刺激表明，在无Ca2+的情况下存在缓慢的磷酸化速率，并且这种磷酸化触发了分泌。添加外源2A型蛋白磷酸酶导致Ca2+依赖性去甲肾上腺素分泌减少了近50%。因此，在无Ca2+和有Ca2+时释放的去甲肾上腺素量似乎都取决于蛋白磷酸化水平。
