Absence of mitochondrial beta-adrenoceptors in guinea pig myocardium: evidence for tissue disparity.
1. Binding sites in guinea pig myocardial tissue labelled by (-)-[125I] cyanopindolol (CYP) were investigated using differential centrifugation and autoradiographic techniques. Autoradiographs of myocardial sections (0.1 microns) indicated (-)-[125I]CYP binding to sarcolemmal membrane. A low density of binding sites was observed to mitochondria. 2. Binding studies were performed in subcellular fractions. The density of binding sites in the mitochondrial fraction (36.1 +/- 9.4 fmol/mg protein) was less than 10% that in the sarcolemmal membrane (371.7 +/- 38.2 fmol/mg protein). The beta 1/beta 2-adrenoceptor subtype ratio in the mitochondrial fraction (83.3/16.7) was similar to that in the sarcolemmal fraction (87.1/12.9). 3. Ouabain (100 microM), in the presence of sodium azide (0.4 mM), inhibited a Na+K+ stimulated ATPase activity (1.0 +/- 0.2 mumol Pi/mg protein/hr reduction), indicating a low but significant level of sarcolemmal contamination of the mitochondrial fraction. 4. The study showed beta-adrenoceptors in guinea pig heart are located primarily on the sarcolemmal membrane of myocardium. No evidence was obtained for beta-adrenoceptors over mitochondria, as has been suggested in other tissues and species, but that this binding was to sarcolemmal inclusions in the mitochondrial fraction.
Russell
F D
FD
Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
Molenaar
P
P
Summers
R J
RJ
D015720:5'-Nucleotidase / Q000378:metabolism; D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D001386:Azides / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism* / Q000648:ultrastructure; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D010042:Ouabain / Q000494:pharmacology; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism; D019810:Sodium Azide; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism
D000319:Adrenergic beta-Antagonists; D001386:Azides; D011943:Receptors, Adrenergic, beta; C047975:cyanopindolol; D010042:Ouabain; D019810:Sodium Azide; D010869:Pindolol; D015720:5'-Nucleotidase; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase