title: Reduction of calcium channel antagonist binding sites by oxygen free radicals in rat heart.
abstract: In view of the importance of Ca2+-channels in controlling the entry of Ca2+ into the myocardium, this study was undertaken to examine the effects of oxygen free radicals on the binding of Ca2+-channel antagonists in rat heart by employing [3H]-nitrendipine as a ligand. Isolated heart membranes were incubated with xanthine + xanthine oxidase (a superoxide anion radicals generating system), hydrogen peroxide (an activated species of oxygen), or hydrogen peroxide + Fe2+ (a hydroxyl radicals generating system). The assay of the [3H]-nitrendipine binding activity revealed that the maximal number of binding sites (Bmax) were reduced in a time-dependent manner by superoxide radicals without any changes in the binding constant (Kd); a significant reduction of Bmax was seen after incubating membranes with xanthine + xanthine oxidase for a 10-min-period. Superoxide dismutase showed a protective effect on the superoxide radicals induced reduction in Bmax. Both hydrogen peroxide and hydroxyl radicals also depressed the Bmax for [3H]-nitrendipine binding without any significant change in Kd; catalase and mannitol showed protective effects on hydrogen peroxide or hydroxyl radicals induced depression in Bmax, respectively. These results indicate that oxygen free radicals may reduce the number of Ca2+-channels in the cell membrane and this change may contribute towards decreasing the voltage-dependent Ca2+ influx in the cardiac cell.
authors.affiliation: Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Kaneko
authors.forename: S L
authors.initials: SL
authors.lastname: Lee
authors.forename: C M
authors.initials: CM
authors.lastname: Wolf
authors.forename: N S
authors.initials: NS
authors.lastname: Dhalla
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D005296:Ferrous Compounds / Q000494:pharmacology; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008297:Male; D009568:Nitrendipine / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D019820:Xanthine; D014969:Xanthine Oxidase / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005296:Ferrous Compounds; D005609:Free Radicals; D014970:Xanthines; D019820:Xanthine; C020748:ferrous sulfate; D009568:Nitrendipine; D006861:Hydrogen Peroxide; D014969:Xanthine Oxidase; D010100:Oxygen