Refined membrane preparations mask ischemic fall in myocardial beta-receptor density.
Most of the previous studies of ischemic myocardial beta-adrenergic receptors have employed membrane preparations in which the initial pellet from the myocardial homogenate spun at a low speed was discarded. We studied changes in beta-adrenergic receptor density ([125I]-iodocyanopindolol; Bmax) during 30 min of coronary occlusion in surgically anesthetized open-chest rabbits using just such a pellet [homogenized heart spun at 1,000 g (1,000-g pellet)], as well as a second pellet from the supernatant of the first pellet [spun at 40,000 g (40,000-g pellet)]. Bmax fell during acute ischemia in the 1,000-g pellet [46.8 +/- 6.1 vs. 21.6 +/- 2.4 (SE) fmol/mg protein; P less than 0.01; n = 7] but did not change in the 40,000-g pellet [46.8 +/- 6.5 vs. 47.9 +/- 2.6 (SE) fmol/mg protein; P = NS; n = 6]. The 1,000-g pellet contained 70.0 +/- 8.1% of the beta-adrenergic receptors measured between the two preparations (P less than 0.05; n = 8) and all of the histamine H2-receptors; therefore, to minimize receptor loss and other potential artifacts, unspun myocardial homogenate was studied. An ischemic decrease in Bmax was still observed [32.9 +/- 2.0 vs. 20.9 +/- 4.1 (SE) fmol/mg protein; P less than 0.05; n = 5]. These results support the use of data from cruder myocardial membrane preparations (e.g., 1,000-g pellet or unspun homogenate), which may be of greater pathophysiological relevance than data derived from a standard more-refined preparation (40,000-g pellet).
Wolff
A A
AA
Cardiovascular Research Institute, University of California, San Francisco.
Hines
D K
DK
Karliner
J S
JS
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002498:Centrifugation; D003327:Coronary Disease / Q000378:metabolism*; D005260:Female; D006632:Histamine / Q000494:pharmacology; D006652:Histological Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D011817:Rabbits; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013237:Stereoisomerism
D011943:Receptors, Adrenergic, beta; D006632:Histamine; D000262:Adenylyl Cyclases; D007545:Isoproterenol