Hashimoto T, Hirata M, Ito Y
Br J Pharmacol. 1985 Sep;86(1):191-9. doi: 10.1111/j.1476-5381.1985.tb09449.x.
To elucidate the role of inositol 1,4,5-trisphosphate (Ins-P3) in the initiation of agonist-induced contraction of the smooth muscle cells of the dog trachea, we investigated the effects of acetylcholine (ACh) on the concentrations of Ins-P3, phosphatidylinositol-4,5-bisphosphate (PI-P2) or phosphatidic acid (PA). The effects of Ins-P3 on the Ca2+ stored in the smooth muscle cells were also studied in saponin-permeabilized smooth muscle cells. A half maximal or maximal Ca2+ accumulation into the cells was observed in the dispersed single, smooth muscle cells treated by saponin, in free Ca2+ concentrations of 4.6 X 10(-7) or 5 X 10(-5)M, respectively. The ATP-dependent Ca2+ accumulation was maximal at 0.63 nmol/10(5) cells. Effects of Ins-P3 on stored Ca2+ were observed at a free Ca2+ concentration of 3.7 X 10(-7)M, which induces about half maximal ATP-dependent Ca2+-accumulation. Ins-P3 released the Ca2+ accumulated by ATP, in a dose-dependent manner. About 40% of the total Ca2+ was released following application of 3 microM Ins-P3. The release of stored Ca2+ induced by application of Ins-P3 was followed by its re-uptake into the smooth muscle cells. Thus, the stored Ca2+ was repeatedly released with repetitive applications of Ins-P3. Application of ACh (10(-5)M) to the dog trachea stimulated the production of Ins-P3 in the soluble fraction and 10s after this application, the relative amount of Ins-P3 was 290% of the control value. 6 Concomitantly, ACh (10- 5 M) either reduced or increased the contents ofphosphatidyl inositol 4,5-biphosphate (PI-P2) or phosphatidic acid (PA) in the lipid fraction ofthe smooth muscle cells to 60% or to 350% of the control value, respectively, thereby indicating that ACh stimulates the phosphodiesteric hydrolysis of PI-P2. 7 5-Hydroxytryptamine (5-HT; 10- 5M) also reduced or increased the contents of PI-P2 or PA to 80 or to 200% of the control values, respectively. However, neither histamine (10-5M), in the presence or absence of cimetidine (10-5M), nor prostaglandin F2 alpha. (PGF2 alpha. 1O-7 M) showed any effect on the contents of PI-P2 or PA in the lipid fraction of the smooth muscle cells. 8 These results indicate that in muscle cells of the dog trachea, Ins-P3 may play the role ofintracellular second messenger in the initiation of ACh or 5-HT-induced contraction, but not in the case of histamine or PGF2 alpha-induced contraction.
为阐明1,4,5-三磷酸肌醇（Ins-P3）在犬气管平滑肌细胞激动剂诱导收缩起始过程中的作用，我们研究了乙酰胆碱（ACh）对Ins-P3、磷脂酰肌醇-4,5-二磷酸（PI-P2）或磷脂酸（PA）浓度的影响。还在皂素通透的平滑肌细胞中研究了Ins-P3对平滑肌细胞内储存Ca2+的影响。在分别为4.6×10(-7)或5×10(-5)M的游离Ca2+浓度下，用皂素处理的分散单个平滑肌细胞中观察到细胞内Ca2+积累达到半最大或最大量。ATP依赖性Ca2+积累在0.63 nmol/10(5)个细胞时达到最大值。在游离Ca2+浓度为3.7×10(-7)M时观察到Ins-P3对储存Ca2+的影响，该浓度诱导约半最大ATP依赖性Ca2+积累。Ins-P3以剂量依赖性方式释放由ATP积累的Ca2+。施加3μM Ins-P3后，约40%的总Ca2+被释放。施加Ins-P3诱导的储存Ca2+释放后，其又被重新摄取到平滑肌细胞中。因此，随着Ins-P3的重复施加，储存的Ca2+被反复释放。向犬气管施加ACh（10(-5)M）刺激了可溶性部分中Ins-P3的产生，施加后10秒，Ins-P3的相对量为对照值的290%。同时，ACh（10-5M）使平滑肌细胞脂质部分中的磷脂酰肌醇4,5-二磷酸（PI-P2）或磷脂酸（PA）含量分别降至对照值的60%或升至对照值的350%，从而表明ACh刺激了PI-P2的磷酸二酯水解。5-羟色胺（5-HT；10-5M）也分别使PI-P2或PA含量降至对照值的80%或升至对照值的200%。然而，组胺（10-5M）无论在有或没有西咪替丁（10-五M）存在的情况下，以及前列腺素F2α（PGF2α 10-7M）对平滑肌细胞脂质部分中的PI-P2或PA含量均无任何影响。这些结果表明，在犬气管的肌肉细胞中，Ins-P3可能在ACh或5-HT诱导的收缩起始过程中起细胞内第二信使的作用，但在组胺或PGF2α诱导的收缩中不起作用。
