Sasakawa N, Nakaki T, Kato R
Department of Pharmacology, Keio University School of Medicine, Tokyo, Japan.
J Biol Chem. 1990 Oct 15;265(29):17700-5.
When [3H]inositol-prelabeled cultured bovine adrenal chromaffin cells were stimulated with high K+ (56 mM) and nicotine (10 microM), a large and transient increase in [3H]inositol 1,3,4,5,6-pentakisphosphate (InsP5) accumulation was observed. The accumulation reached the maximum level at 15 s and then declined to the basal level at 2 min. The time course of accumulation of InsP5 was parallel to that of [3H]inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). Angiotensin II (Ang II) (10 microM) rapidly accumulated InsP5, but the level was sustained for 2 min. With a slower time course and a lesser amount than InsP5, high K+, nicotine, and Ang II caused an accumulation of [3H]inositol 1,3,4,5-tetrakisphosphate and [3H]inositol hexakisphosphate. Veratridine (100 microM), maitotoxin (10 ng/ml), ATP (30 microM), platelet-derived growth factor (10 ng/ml), and endothelin (10 ng/ml) also induced the InsP5 accumulation. High K+, nicotine, veratridine, and maitotoxin induced an increase in 45Ca2+ uptake, whereas Ang II, ATP, platelet-derived growth factor, and endothelin did not cause 45Ca2+ uptake. Nifedipine, a calcium channel antagonist, inhibited the high K(+)-induced InsP5 accumulation but failed to affect the Ang II-induced InsP5 accumulation. In an EGTA-containing and Ca2(+)-depleted medium, the high K(+)-induced InsP5 accumulation was completely inhibited, whereas the InsP5 accumulation induced by Ang II was not significantly inhibited. 12-O-tetradecanoylphorbol-13-acetate inhibited partially the Ang II-induced InsP5 accumulation but failed to inhibit the high K(+)-induced accumulation. In those experiments, the changes of InsP5 accumulation were closely correlated to those of Ins(1,4,5)P3. In the chromaffin cell homogenate, [3H] Ins(1,4,5)P3 was converted eventually to [3H]InsP5 through [3H]inositol 1,3,4,6-tetrakisphosphate. Taken together, the above results suggest that InsP5 is rapidly formed by a variety of stimulants and that the formation of InsP5 may occur through two mechanisms, i.e. Ca2+ uptake-dependent and Ca2+ uptake-independent ones in cultured adrenal chromaffin cells.
当用高钾（56 mM）和尼古丁（10 μM）刺激预先用[3H]肌醇标记的培养牛肾上腺嗜铬细胞时，观察到[3H]肌醇1,3,4,5,6 - 五磷酸（InsP5）积累出现大幅且短暂的增加。积累在15秒时达到最高水平，然后在2分钟时降至基础水平。InsP5的积累时间进程与[3H]肌醇1,4,5 - 三磷酸（Ins(1,4,5)P3）的积累时间进程平行。血管紧张素II（Ang II）（10 μM）迅速积累InsP5，但该水平持续2分钟。与InsP5相比，高钾、尼古丁和Ang II引起[3H]肌醇1,3,4,5 - 四磷酸和[3H]肌醇六磷酸积累的时间进程较慢且量较少。藜芦碱（100 μM）、 maitotoxin（10 ng/ml）、ATP（30 μM）、血小板衍生生长因子（10 ng/ml）和内皮素（10 ng/ml）也诱导InsP5积累。高钾、尼古丁、藜芦碱和maitotoxin诱导45Ca2+摄取增加，而Ang II、ATP、血小板衍生生长因子和内皮素未引起45Ca2+摄取。钙通道拮抗剂硝苯地平抑制高钾诱导的InsP5积累，但未能影响Ang II诱导的InsP5积累。在含有EGTA且Ca2+耗尽的培养基中，高钾诱导的InsP5积累被完全抑制，而Ang II诱导的InsP5积累未被显著抑制。12 - O - 十四烷酰佛波醇 - 13 - 乙酸盐部分抑制Ang II诱导的InsP5积累，但未能抑制高钾诱导的积累。在这些实验中，InsP5积累的变化与Ins(1,4,5)P3的变化密切相关。在嗜铬细胞匀浆中，[3H]Ins(1,4,5)P3最终通过[3H]肌醇1,3,4,6 - 四磷酸转化为[3H]InsP5。综上所述，上述结果表明InsP5可由多种刺激物快速形成，且在培养的肾上腺嗜铬细胞中，InsP5的形成可能通过两种机制发生，即钙摄取依赖性和钙摄取非依赖性机制。
