title: Effect of age on potassium- and tyramine-induced release of norepinephrine from cardiac synaptosomes in male F344 rats.
abstract: Potassium (K+)-induced norepinephrine (NE) release was examined in preparations of cardiac synaptosomes and sliced atria from 6-, 24-, and 26-mo-old male F344 rats. Cardiac synaptosomes were prepared from rat hearts by collagenase digestion followed by homogenization in 0.32 M sucrose and centrifugation. The synaptosome preparations and the sliced atria were labeled with 3H-NE and then placed in a superfusion system. K(+)-induced net fractional release of NE from synaptosomes prepared from 24- and 26-mo-old rats (4.3% and 3.0%, respectively) was significantly reduced when compared to NE release from synaptosomes from 6-mo-old rats (5.2%). K(+)-induced NE release from sliced atria from 24-mo-old rats (4.7%) was also significantly reduced when compared to NE release from atria from 6-mo-old rats (6.3%). Perfusion of cardiac synaptosomes with buffer prepared without calcium (CA++free, < 5 microM) reduced K(+)-induced release by 50% in all age groups studied. Perfusion with tyramine induced identical rates of NE release from cardiac synaptosomes prepared from 6- and 24-mo-old rats. These results confirm that depolarization-induced NE release from cardiac sympathetic nerves is reduced in the old male F344 rat.
authors.affiliation: Department of Pharmacology, Medical College of Pennsylvania, Philadelphia.
authors.forename: D L
authors.initials: DL
authors.lastname: Snyder
authors.forename: V J
authors.initials: VJ
authors.lastname: Aloyo
authors.forename: H B
authors.initials: HB
authors.lastname: McIlvain
authors.forename: M D
authors.initials: MD
authors.lastname: Johnson
authors.forename: J
authors.initials: J
authors.lastname: Roberts
mesh_terms: D000320:Adrenergic Fibers / Q000378:metabolism; D000375:Aging / Q000378:metabolism*; D000818:Animals; D003891:Desipramine / Q000494:pharmacology; D006321:Heart / Q000294:innervation*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D016627:Oxidopamine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013574:Synaptosomes / Q000378:metabolism*; D014439:Tyramine / Q000494:pharmacology*
chemical_list: D011506:Proteins; D016627:Oxidopamine; D011188:Potassium; D003891:Desipramine; D009638:Norepinephrine; D014439:Tyramine