Pertussis toxin, but not tyrosine kinase inhibitors, abolishes the
effects of u50,488h on cytosolic ca2+ in myocytes.
Sheng, Jian-Zhong, Nai Sum Wong, Hong-Xin Wang, and Tak Ming Wong.
Departments of Physiology and Biochemistry, Faculty of Medicine,
The University of Hong Kong, Hong Kong
APStracts 3:0307C, 1996.
The effects of trans-3,4-dichloro-N-[2-(1
-pyrrolidinyl)cyclohexyl]benzeacetamidel (U50,488H), a k-opioid
receptor agonist, at 10-5 M on cytosolic calcium ([Ca2+]i) and
[Ca2+]i transient in quiescent and electrically-stimulated rat
ventricular myocytes, respectively were determined after the cells
had been pretreated with pertussis toxin (PTX) or tyrosine kinase
inhibitors, genistein or tyrphostin. The [Ca2+]i was determined with
a spectrofluorimetric method, using fura-2 as Ca2+ indicator.
U50,488H at 10-5 M itself induced a [Ca2+]i transient in the
quiescent cells, but inhibited the [Ca2+]i transient in electrically
-stimulated cells. The effects of U50,488H (10-5 M) on [Ca2+]i, which
were blocked by a selective k-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
(5x10-5 M ) for 30 min. 1-[6-[[(17b)-3-Methoxyestra-1,3,5(10)-trien
-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122), an inhibitor of
phospholipase C (PLC), 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 (U73343), also blocked the Ca2+
responses to U50,488H. The results indicate that activation of PLC
upon k-opioid receptor stimulation is via PTX sensitive G-proteins,
but does not involve protein tyrosine phosphorylation.
Received 27 June 1996; accepted in final form 12 September 1996.
APS Manuscript Number C364-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996