title: SR Ca2+ pump heterogeneity in coronary artery: free radicals and IP3-sensitive and -insensitive pools.
abstract: Reactive oxygen species are known to decrease the action of agents that 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 myo-inositol 1,4,5-trisphosphate (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 sodium azide. IP3 caused a release of up to 65% of the loaded 45Ca2+, whereas the Ca2+ ionophore A-23187 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 s. The 50% effective concentration for IP3 was 2.7 +/- 1.0 microM at pH 6.8 and 37 degrees C. At pH 7.4 the IP3-induced Ca2+ release was slightly lower than at pH 6.4-6.8. The IP3-induced release was also inhibited by Ca2+ concentration 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 -insensitive Ca2+ pools. In contrast, 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 heterogeneous: those required to pump Ca2+ into the IP3-sensitive pool are inhibited by peroxide and superoxide, but those loading the IP3-insensitive pool are inhibited by peroxide only.
authors.affiliation: Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: A B
authors.initials: AB
authors.lastname: Elmoselhi
authors.forename: S E
authors.initials: SE
authors.lastname: Samson
authors.forename: A K
authors.initials: AK
authors.lastname: Grover
mesh_terms: D000818:Animals; D001386:Azides / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005609:Free Radicals / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010545:Peroxides / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019810:Sodium Azide; D013481:Superoxides / Q000494:pharmacology; D013552:Swine; D013696:Temperature
chemical_list: D001386:Azides; D015220:Calcium Channels; D005609:Free Radicals; D010545:Peroxides; D013481:Superoxides; D000001:Calcimycin; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D019810:Sodium Azide; D000252:Calcium-Transporting ATPases; D002118:Calcium