title: The effects of Ca(2+)-free perfusion and the calcium paradox on [125I] endothelin-1 binding to rat cardiac membranes.
abstract: The binding characteristics of [125I]endothelin-1 (ET-1) to cardiac membranes isolated from rat hearts subjected to Ca(2+)-free perfusion or the Ca2+ paradox were examined. The effect of treatment with 2, 3 butanedione monoxime (BDM), which inhibits the tissue damage associated with the calcium paradox, was also investigated. Membranes from rat hearts perfused under control conditions bound [125I]ET-1 to a single population of sites with a Bmax of 107.7 +/- 3.7 fmol/mg protein and an affinity (KD) of 153 +/- 12 pM. Ten minutes of Ca(2+)-free perfusion resulted in a significant (P < 0.01) increase in Bmax to 167.5 +/- 8.3 fmol/mg protein without change in KD. Ca2+ repletion following Ca(2+)-free perfusion tended to increase further the Bmax (180.6 +/- 10.4 fmol/mg protein) without change in KD. Treatment with BDM attenuated but did not prevent the rise in Bmax following Ca(2+)-free perfusion. Following Ca2+ repletion, however, Bmax returned to control levels in the BDM treated group. These changes were not associated with changes in the ability of ET-1 and ET-3 to inhibit [125I]ET-1 binding. The results demonstrate that Ca(2+)-free perfusion is associated with an increase in the binding site density of [125I]ET-1 which is maintained or further increased upon Ca2+ repletion. If, however, the tissue damage associated with the Ca2+ paradox is prevented with BDM, Ca2+ repletion is associated with a reversal of the increase due to Ca(2+)-free perfusion.
authors.affiliation: Department of Medicine, University of Melbourne, Austin Hospital, Heidelberg, Vic., Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Daly
authors.forename: R
authors.initials: R
authors.lastname: Ou
authors.forename: X H
authors.initials: XH
authors.lastname: Gu
authors.forename: D J
authors.initials: DJ
authors.lastname: Casley
authors.forename: W G
authors.initials: WG
authors.lastname: Nayler
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D016232:Endothelins / Q000378:metabolism*; D005260:Female; D006321:Heart / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D007457:Iodine Radioisotopes; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D010477:Perfusion; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D017466:Receptors, Endothelin / Q000187:drug effects / Q000378:metabolism
chemical_list: D016232:Endothelins; D007457:Iodine Radioisotopes; D008565:Membrane Proteins; D017466:Receptors, Endothelin; C004717:diacetylmonoxime; D003931:Diacetyl; D002118:Calcium