Heterogeneity in the effects of reactive oxygen on coronary artery
ca2+ pumps loading ip3 -sensitive and -insensitive sr ca2+ pools.
Elmoselhi, A. B., S. E. Samson, and A. K. Grover.
Department of Biomedical Sciences, McMaster University, Hamilton,
Ontario, Canada L8N3Z5
APStracts 3:0179C, 1996.
Reactive oxygen species (ROS) are known to decrease the action of
agents which mobilize Ca2+ from sarcoplasmic reticulum (SR) in pig
coronary artery smooth muscle. Potentially, this may be due to damage
to the SR Ca2+ pump or to the IP3-induced Ca2+ release channels. Here
we report on the effects of peroxide and superoxide on the SR Ca2+
pump and the subsequent IP3-induced Ca2+ release. Smooth muscle cells
cultured from pig left coronary arteries were permeabilized using
saponin and then loaded with 45Ca2+ in the presence of an ATP
-regenerating system and the mitochondrial Ca2+ uptake inhibitor Na+
-azide. IP3 caused a release of upto 65% of the loaded 45Ca2+ while
the Ca2+ ionophore A23187 caused a release of > 95%. The nature
of the IP3-insensitive component of the Ca2+ uptake is not known. The
IP3-induced Ca2+ release occurred at 0 or 37 degrees C and was
complete in <30 sec. The EC50 value for IP3 was 2.7+/-1.0 [mu]M
at pH 6.8 and 37 degrees C. At pH 7.4, the IP3-induced Ca2+ release
was slightly lower than at pH 6.4 to 6.8. The IP3-induced release was
also inhibited by [Ca2+] in the release medium. To investigate the
effects of peroxide or superoxide, the cells were treated with these
agents, washed, skinned and then used to examine the IP3-sensitive
and -insensitive Ca2+ pools under the conditions in which the IP3
-sensitive pool was 60-65% of the total. Peroxide pretreatment was
equipotent in inhibiting loading into the IP3-sensitive and the
-insensitive Ca2+ pools. In contrast, the superoxide pretreatment
inhibited loading into the IP3-sensitive pool but not into the IP3
-insensitive pool. These data are consistent with a model in which the
SR Ca2+ pumps are heterogenous: those required to pump Ca2+ into the
IP3-sensitive pool are inhibited by both peroxide and superoxide but
those loading the IP3-insensitive pool are inhibited by peroxide
only.
Received 5 February 1996; accepted in final form 22 May 1996.
APS Manuscript Number C67-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96