Attenuation of endothelin-1-induced calcium response by tyrosine
kinase inhibitors in vascular smooth muscle cells.
Liu, Cynthia Y., and Michael Sturek.
Vascular Biology Laboratory, Dalton Cardiovascular Research Center
and Department of Physiology, School of Medicine, University of
Missouri, Columbia, MO 65211
APStracts 3:0009C, 1996.
Although tyrosine kinases play an important role in cell growth and
have been implicated in regulation of smooth muscle contraction,
their role in agonist-induced myoplasmic Ca2+ responses is unclear.
We examined effects of the tyrosine kinase inhibitors genistein and
methyl 2,5-dihydroxycinnamate (MDHC) on the endothelin-1 (ET-1)
-induced Ca2+ response and determined underlying mechanisms for the
effects. Freshly isolated smooth muscle cells from porcine coronary
arteries were loaded with fura-2 ester and myoplasmic free Ca2+
concentration (Ca+) was estimated with fura-2 microfluorometry. Both
genistein and MDHC inhibited the initial transient Ca+ response to ET
by 54% and 81%, respectively (p<0.05), in the presence of
extracellular Ca2+. Genistein also significantly delayed the Ca+
response, the latent period from ET-1 application to the beginning of
the Ca+ response being increased from 1.08+/-0.17 min. to 2.65+/-0.52
min. (p<0.05). In the absence of extracellular Ca2+, genistein
inhibited the ET-1-induced Ca+ response by 93% ( p<0.05). The
Ca+ responses to caffeine (5 mM) or IP3 applied intracellularly via a
patch clamp pipette were not affected by genistein. Both genistein
and MDHC also abolished the sustained Ca+ response to ET-1. However,
the Ca+ response to depolarization by 80 mM K was not inhibited by
MDHC and only inhibited 22% by genistein (p<0.05). These results
indicate that 1) activation of tyrosine kinases is an important
regulatory mechanism for the ET-1-induced Ca+ response in vascular
smooth muscle and 2) tyrosine kinases mediate ET-1-induced Ca2+
release with no direct effect on IP3-mediated Ca2+ release . Thus,
ET-1-mediated signaling upstream of IP3 interaction with the Ca2+
stores is regulated by tyrosine kinases.
Received 13 September 1995; accepted in final form 12 December
1995.
APS Manuscript Number C555-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96