Marathe G K, Yousufzai S Y, Abdel-Latif A A
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100, USA.
Biochem Pharmacol. 1996 Oct 25;52(8):1261-9. doi: 10.1016/0006-2952(96)00481-9.
The purpose of the present study was to examine the mechanism of the stimulatory effect of substance P (SP) on cyclic AMP (cAMP) accumulation in dog iris sphincter. We found that: (1) SP increased cAMP accumulation in a time- and concentration-dependent manner, the T1/2 and EC50 values being 1.2 min and 44 nM, respectively. SP has no effect on inositol trisphosphate and muscle contraction in this tissue. (2) SP-stimulated cAMP formation was inhibited by quinacrine, a non-specific phospholipase A2 inhibitor (IC50 = 9.5 microM), and by indomethacin (Indo), a cyclooxygenase inhibitor (IC50 = 3.5 nM), in a concentration-dependent manner, suggesting that SP induces cAMP accumulation via an Indo-sensitive pathway. (3) SP-induced arachidonic acid release and SP-induced prostaglandin E2 (PGE2) release were inhibited concentration dependently by quinacrine and Indo, with IC50 values of 11 microM and 0.8 nM, respectively. (4) PGE2 (1 microM) increased cAMP formation in the sphincter muscle by 94%, and, furthermore, the PG, but not SP, stimulated the activity of adenylyl cyclase in membrane fractions isolated from this tissue. (5) Indo (1 microM) blocked the relaxing effect of SP (1 microM) in iris sphincter precontracted with carbachol (1 microM). (6) The inhibitory effect of Indo on SP-induced cAMP accumulation was species specific. Increases in cAMP represent a mechanism by which extracellular SP can regulate smooth muscle function. Thus, we conclude from these studies that in dog iris sphincter SP-induced cAMP accumulation is mediated through PGs, and that in this cholinergically innervated muscle SP via cAMP could function, in part, to modulate the physiological responses to muscarinic receptor stimulation.
本研究的目的是探讨P物质（SP）对犬虹膜括约肌中环磷酸腺苷（cAMP）积累的刺激作用机制。我们发现：（1）SP以时间和浓度依赖性方式增加cAMP积累，T1/2和EC50值分别为1.2分钟和44 nM。SP对该组织中的肌醇三磷酸和肌肉收缩无影响。（2）SP刺激的cAMP形成受到喹吖因（一种非特异性磷脂酶A2抑制剂，IC50 = 9.5 microM）和吲哚美辛（Indo，一种环氧化酶抑制剂，IC50 = 3.5 nM）的浓度依赖性抑制，表明SP通过Indo敏感途径诱导cAMP积累。（3）喹吖因和Indo浓度依赖性抑制SP诱导的花生四烯酸释放和SP诱导的前列腺素E2（PGE2）释放，IC50值分别为11 microM和0.8 nM。（4）PGE2（1 microM）使括约肌肌肉中的cAMP形成增加94%，此外，前列腺素而非SP刺激从该组织分离的膜组分中的腺苷酸环化酶活性。（5）Indo（1 microM）阻断了SP（1 microM）对用卡巴胆碱（1 microM）预收缩的虹膜括约肌的松弛作用。（6）Indo对SP诱导的cAMP积累的抑制作用具有物种特异性。cAMP的增加代表细胞外SP调节平滑肌功能的一种机制。因此，我们从这些研究中得出结论，在犬虹膜括约肌中，SP诱导的cAMP积累是通过前列腺素介导的，并且在这种胆碱能神经支配的肌肉中，SP通过cAMP可能部分发挥作用，以调节对毒蕈碱受体刺激的生理反应。
