Pertussis toxin, but not tyrosine kinase inhibitors, abolishes effects of U-50488H on [Ca2+]i in myocytes
Sheng, J.Z.; Wong, N.S.; Wang, H.X.; Wong, T.M.
American Journal of Physiology 272(2 Pt 1): C560-C564
1997
ISSN/ISBN: 0002-9513 PMID: 9124299 Document Number: 472836
The effects of 10-5 M trans-3,4-dichloro-N-(2-(1-pyrrolidinyl)cyclohexyl)benzeacetamidel (U-50488H), a kappa-opioid receptor agonist, on cytosolic Ca-2+ concentration ((Ca-2+)-i) and the (Ca-2+)-i transient in quiescent and electrically stimulated rat ventricular myocytes, respectively. were determined after the cells had been pretreated with pertussis toxin (PTX) or a tyrosine kinase inhibitor (genistein or tyrphostin). The (Ca-2+)-i was determined with a spectrofluorometric method, with fura 2 as Ca-2+ indicator. U-50488H at 10-5 M itself induced a (Ca-2+), transient in the quiescent cells but inhibited the (Ca-2+)-i transient in electrically stimulated cells. The effects of 10-5 M U-50488H on (Ca-2+)-i, which were blocked by a selective kappa-opioid receptor antagonist, nor-binaltorphimine (10-6 M), were abolished after pretreatment with PTX (1 mu-g/ml) for 24 h, but not with genistein (10-4 M) or tyrphostin (5 times 10-5 M) for 30 min. 1-(6-(((17b)-3-Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U-73122), an inhibitor of phospholipase C, at 10-5 M, but not its inactive structural isomer 1-(6-(((17b)-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-2,5-pyrrolidinedione (U-73343), also blocked the Ca-2+ responses to U-50488H. The results indicate that activation of phospholipase C on kappa-opioid receptor stimulation is via PTX-sensitive G proteins but does not involve protein tyrosine phosphorylation.