Potentiation of bradykinin-induced inositol phosphates production by cyclic AMP elevating agents and endothelin-1 in cultured astrocytes
✍ Scribed by Ching-C. Chen; Jacque Chang; Wei C. Chen
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 800 KB
- Volume
- 16
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
Cultured astrocytes express bradykinin (BK) receptors, which are coupled to phospholipase C (PLC) through G-protein to mediate phosphoinositide (PI) hydrolysis. The regulation of this BK receptor-G protein-PLC pathway by CAMP and endothelin-1 (ET-1) was explored by short-term (20 min) and long-term (24 h) treatment with 100 pM dibutyryl cyclic AMP (dBcAMP) or 10 nM ET-1. Short-term treatment of cells with dBcAMP had no effect on BK-induced PI hydrolysis; however, long-term treatment resulted in potentiation of the BK response. Similar effects were seen after 10 pM forskolin pretreatment ofthe cells. We further explored the site of action of 24 h dBcAMP pretreatment and found that AlF4-, ionomycin-or A23187-induced PI hydrolysis was not affected but L3HIBK binding was increased. These results indicate that the site of action of dBcAMP is the BK receptor and Scatchard plot analysis showed that the Bmax was increased but the Kd decreased. Cycloheximide (0.5 FM) blocked the increase in ['HlBK binding, indicating that new synthesis of receptor protein might occur during 24 h pretreatment with dBcAMP. Twenty minutes pretreatment of cells with ET-1 resulted in desensitization of the ET-1 induced PI response, while the BK response was unaffected. After 24 h pretreatment with ET-1, desensitization to ET-1 still occurred, while BKinduced PI hydrolysjs was markedly potentiated. [3HlBK binding and AlF,--induced but not A23187-or ionomycin-induced PI hydrolysis were increased, indicating that the site of action of long-term ET-1 treatment was the BK receptor and G protein; Scatchard analysis showed a n increase in Bmax but no effect on Kd. These effects were blocked by cycloheximide, indicating that new synthesis of both receptor protein and G protein might occur during 24 h pretreatment with ET-1. P'HlThymidine uptake was inhibited or potentiated by dBcAMP and ET-1, respectively. Possible dBcAh4P-induced differentiation and ET-1-induced proliferation may contribute to the increased expression of receptor proteins.